BuUetin No. 208 Series B, Descriptive Geology, 27 DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY CHARLES II. WALCOTT, Directok DESCRIPTIVE GEOLOGY OF- NEVADA SOUTH OF THE FORTIETH PARALLEL AND ADJACENT PORTIONS OF CALIFORNIA BY JOSIAH EDWARD SPURR WASHINGTON GOVERNMENT PRINTING OFFICE 1903 r-7 V r I D ^ SEP 3 W^ CONTENTS. Page. Introduction 15 Exj)lanation of formation names 18 Anbrey limestone and sandstone 18 dinar series 18 Diamond Peak qtiartzite 18 Esmeralda formation 19 Eureka qtiartzite 19 Grand Canyon group 19 Hamburg limestone and shale 19 Humboldt series 20 Koipato formation 20 Lone Mountain limestone ^ 20 Nevada limestone 20 Ogden quartzite . 20 Pogonip formation 21 Prospect Mountain limestone and quartzite , 21 Red Wall limestone 21 Secret Canyon sliale 22 Star Peak formation 22 Tonto sliale and sandstone 22 Truckee formation 22 Unkar formation 23 Wasatch limestone 23 Weber conglomerate 23 White Pine shale 23 Chapter I. — Ranges of east-central Nevada 25 Snake Range 25 Topography . 25 Archean rocks 26 Sedimentary rocks 27 Cambrian 27 Silurian 30 Carboniferous - 32 Mesozoic or Tertiary . 33 Pliocene 34 Pleistocene 34 Igneous rocks ' 35 Lavas 35 Dike rocks 35 Structure 1 35 Folds 35 Faults - 35 Ores- 36 3 4 CONTENTS. Chapter I. — Ranges of east-central Nevada — Contintied. Page. Cedar Range and Clover Valley Mountains 36 Antelope Range 37 Sedimentary rocks 37 Igneons rocks -" 37 Structure 38 Scliell Creek and Highland ranges .- 38 Sedimentary rocks 38 Cambrian 38 Silurian 42 Devonian . 48 Carboniferous 43 Igneous rocks 44 Lavas 44 Dikes 44 Structure 44 Folding •- - - - 44 Faulting 45 Egan Range 47 Topography -- 47 Archean rocks - . . . 47 Sedimentary rocks ' 47 Cambrian --. __- 47 Silurian j 48 Devonian 49 Carboniferous 51 Igneous rocks 52 Lavas 53 Dikes ■- 53 Structure 1 — 53 Folding 53 Faulting 54 Ores -• --- 54 Long Valley Range . 54 Topography 55 Sedimentary rocks . _ - 55 Carboniferous 55 Igneous rocks 56 Lavas : ■ 56 Structure 56 Folding 56 Golden Gate Range _ - 57 Topography 57 Sedimentary rocks . 57 Silurian 57 Devonian 58 Pleistocene 58 Igneoiis rocks 58 Structure 59 Folding . 59 Faulting • 59 Humboldt Range 59 Topography . 59 Sedimentary rocks 60 CONTENTS. • 5 Chapter I. — Ranges of east-central Nevada — Continned. Page. HnmlDoldt Kange — Continned. Igneous rocks 61 Structure 61 Folding 61 Faulting , . . 61 White Pine Range 61 Topography 62 Sedimentary rocks 62 Cambrian 1 . 62 Silurian 63 Devonian - 63 Carboniferous 63 Rhyolite ash 65 Igneous rocks 65 Lava 65 Granite 65 Structure . 65 Folding 65 Faulting :. 66 Relation of topography to structure 67 Ores . 68 Quinn Canyon and G-rant ranges 68 Topogi'aphy 68 Sedimentary rocks 69 Cambrian 69 Silurian 69 Devonian 71 Carboniferous . 72 Pliocene . 72 Igneous rocks 72 Rhyolite and granite 72 Basaltic volcanics 73 Quartz-latites •> 73 Relative age of lavas --- 73 Structure ---. 73 Folding 73 Faulting 75 Relation of structure to topography 75 Worthington Mountains 76 Sedimentary rocks 76 Igneous rocks 76 Structure 77 Pancake Range 77 Topography 77 Sedimentary rocks 77 Carboniferous 77 Devonian 78 Tertiary . 78 Pleistocene lake deposition 79 Gulch dumps or alluvial fans 79 Igneous rocks 79 Structure 80 Folding . 80 Faulting 80 6 CONTENTS. Chapter I.— Ranges of east-central Nevada — Continued. Page. Pancake Range — Continued. Coal 81 Diamond Range 81 Topography 81 Sedimentary rocks .. 81 Igneous rocks . _ 83 Structiire ■ . 83 Relation of structure to topography 84 Ores 84 Hot Creek Range 84 Sedimentary rocks 85 Silurian 85 Tertiary .. ._ 86 Igneous rocks 87 Lavas 87 Structure 87 Ores . 87 Pinon Range . 88 Topography 88 Sedimentary rocks _ . 88 Igneous rocks 88 Volcanic rocks 88 Structtire . 89 Monitor Range 89 Wahweah Range 89 Toquima Range ' 90 Topography 90 Sedimentary rocks 90 Igneous rocks 92 Lavas - 92 Dike rocks 92 Structure : 92 Ores - 93 Toyabe Range 93 Topography 93 Sedimentary rocks _.__. 94 Cambrian 94 Silurian 95 Devonian 95 Carbonif erotis . 95 Tertiary '--. 95 Igneous rocks 95 Granite 95 Rhyolite 96 Augite-basalt 96 Relative age of the igneous rocks 96 Structure 96 Ores 97 Chapter II. —Ranges of west-central Nevada 98 Reese River Range 98 Topography 98 Igneous rocks 99 Age of lavas 99 CONTENTS. 7 Chapter II. — Ranges of west-central Nevada — Continued. Page. Ellsworth Range 99 Sedimentary rocks - 99 Igneous rocks 102 Structure 1 02 Ores : 103 Pilot Mountains 103 Sedimentary rocks 103 Early Tertiary or Mesozoic series . 103 Pliocene. 104 Igneous rocks . 105 Pleistocene oli vine-basalt 105 Granitic rocks 105 Monte Cristo Moimtains , ... 105 Sedimentary rocks 105 Igneous rocks .... 106 Desert Mountains 106 Gabbs Valley and Gabbs Valley Range 107 Sedimentary rocks 107 Early Tertiary marls 107 Pleistocene 108 Igneous rocks 108 Excelsior Range 109 Sedimentary rocks 109 Limestone series (early Tertiary) 109 Sandstone-shale series (early Tertiary or Mesozoic?) 110 Pliocene 111 Igneous rocks 112 Lava . ---^ 112 Granitic rocks 112 Structiire 112 Ores - 113 Resume 113 Candelaria Mountains 1 : 113 Sedimentary rocks 113 Cambrian 113 Carboniferous 113 Earlier Tertiary 114 Pliocene beds 114 Igneous rocks : 114 Walker River Range 115 Igneous rocks 115 Granular rocks 115 Lavas . 116 Igneous rocks showing transitions of texture 116 Sedimentary rocks 116 Pleistocene 116 Pre-Lahontan sediments 117 Smith Valley Range 1 117 Igneous rocks 118 Sedimentary rocks 119 Pine Nut Range . . 120 Topography 120 Igneous rocks.. 120 « CONTENTS. Chapter II — Ranges of west-central Nevada — Continued. Page. Pine Nut Range — Continued. Sedimentary rocks 122 Triassic limestone 122 Pliocene deposits ... 123 Sweetwater Range. , ■. 125 Topography 125 Igneous rocks 126 Post-Pliocene basaltic lava 126 Late rhyolitic lava 126 Late andesite and latite 126 Earlier andesites 127 Earlier rhyolite 127 G-ranitic rocks . . . 127 Sedimentary rocks _ . _' . . 128 Pliocene deposits 128 Resume '. 128 Virginia Range 129 Igneous rocks 129 Sedimentary rocks 130 Ancient limestones 130 Chapter III. — Ranges of southern Nevada 131 Virgin Range _ _ 131 Sedimentary rocks . 131 Pre-Tertiary : 131 Pliocene . 131 Igneous rocks 132 Structure . .. 132 Colorado Canyon 133 Mormon Range 134 Sedimentary rocks 134 Carboniferous 134 Pliocene 1 : _ _ _ _ _ _ 135 Igneous rocks ._.... . . 135 , Structure . 135 Muddy Range 136 Sedimentary rocks 137 Carboniferous 137 Mesozoic 137 Tertiary 137 Igneous rocks 138 Structure 138 Colorado Range ... 138 Eldorado Range . 139 Meadow Valley Canyon . 139 Topography ... . 139 Paleozoic rocks 140 Rhyolite 140 Rhyolite-sandstone series . _ ....... 140 Andesite-latite series 141 Reddish dacites and rhyolites and associated sediments 142 Pliocene beds 143 Pliocene rhyolites 146 Pleistocene rhyolite and basalt 146 CONTENTS. 9 Chapter III. — Ranges of soiitliern Nevada— Continiied. Page. Meadow A^alley Canyon— Continued. Pleistocene gravels .. 147 Sequence of events 147 Meadow Valley Range 148 Sedimentary rocks 149 Cambrian 149 Carbonif eroiis ._ 149 Pliocene 150 Igneous rocks 150 Structure 150 Pahroc Range 151 Igneous rocks 151 Sedimentary rocks '- 152 Structure 153 Hiko Range ' 153 Sedimentary rocks 152 Igneous rocks 153 Structure 153 Pahranagat Range 153 Sedimentary rocks ^ 153 Igneous rocks — --1 154 Structure 154 Arrow Canyon Range 154 Las Vegas Range . 155 Sedimentary rocks . 155 Cambrian 155 Silurian 156 Devonian 156 Carboniferous 156 Pleistocene 157 Structure 157 Timpahute Range 159 Sedimentary rocks 159 Igneous rocks 159 Structure . 160 Ore deposits 160 Desert Range . 160 Sedimentary rocks 160 Silurian 160 Devonian 161 Structure --- 161 Reveille Range -.- 161 Topography 163 Sedimentary rocks 162 Tertiary " 163 Igneous rocks • 163 Relative age of igneous rocks 163 Ore deposits 163 Belted Range 163 Sedimentary rocks 164 Cambrian • 164 Igneous rocks '. 164 Volcanic rocks 164 Structure... 164 10 CONTENTS. Chapter III. — Ranges of southern Nevada — Continued. Page. Spring Mountain Range / 164 Sedimentary rocks 164 Cambrian 164 Carboniferous • 164 Lower Carboniferous 169 Carboniferous red beds . 169 Upper Carboniferous limestone 170 Correlation with Grand Canyon section . . 172 Mesozoic 173 Igneous rocks 174 Structure 175 Ore deposits 180 Area south of Spring Mountain 180 Kawich Range 181 Topography 181 Sedimentary rocks 181 Tertiary . . 181 Igneous rocks 1 181 Ralston Desert 181 Igneous rocks .. 182 Rhyolites 182 Basalt 183 Sedimentary rocks 183 Tertiary 183 Pleistocene 188 Lone Mountain - 188 Igneous rocks . , - - 184 Sedimentary rocks. 184 Silver Peak Range - 184 Sedimentary rocks . 184 Cambrian 184 Silurian ■ 185 Early Tertiary 185 Pliocene 185 Igneous rocks 186 Granites .-_ 186 Volcanic rocks -- 186 Ore deposits 186 Chapter IV. — Great Basin ranges of California, north of Mohave Desert 187 Grapevine and Funeral ranges 187 Sedimentary rocks - - 188 Silurian 188 Devonian : - - 188 Tertiary - 189 Pleistocene 191 Igneous rocks -- - 192 Granular rocks 192 Olivine-basalt at Furnace Creek 192 Andesite at Furnace Creek . 192 Volcanics north of Furnace Creek 192 Structure 193 Resume 194 CONTENTS. 11 Chapter IV. — Great Basin ranges of California, etc.— Continued. Page. Amargosa Valley 195 Metamorpliic rocks 195 Sedimentary rocks 195 Tertiary 195 Structure 195 Kingston Range 195 Sedimentary rocks 196 Cambrian 196 Devonian . 197 Mesozoic 198 Tertiary 198 Igneous rocks 199 Structure :.-_._..-_ 199 Opal or Clarks Peak Mountains 200 Ore deposits 200 Panamint Range 200 Sedimentary rocks - . 201 Cambrian 201 Silurian and Carboniferous .._.--- 202 Early Tertiary 202 Late Tertiary - 202 Pleistocene _ - . 203 Igneous rocks 203 Granite 203 Volcanic rocks - 203 Structure---- 204 Ore deposits 205 Leacli Point and Burnt Rock Mountains 205 Sedimentary rocks 205 Limestone 205 Eocene 206 Igneous rocks 206 Granite 206 Volcanic rocks 206 Structure .- 206 White Mountain Range 206 Topography 207 Sedimentary rocks 207 Cambrian 207 Silurian 208 Carboniferous 208 Triassic --- - 208 Pliocene 209 Igneous rocks 210 Granitic rocks - 210 Volcanic rocks 211 Ore deposits 211 Structiire 212 Darwin or Argus Range 212 Sedimentary rocks • 212 Igneous rocks 212 Granite 212 Volcanic rocks 212 Ore deposits ._ - - 213 12 CONTENTS. Chapter IV. — Great Basin ranges of California, etc. — Continued. Page. Slate Range 313 Sedimentary rocks 213 Paleozoic _.... 213 Tertiary . 213 Igneous rocks 213 Volcanic rocks 213 Coso Range 214 Igneous rocks 214 Granite 214 Volcanic rocks 214 El Paso Range . _' 214 Sedimentary rocks 214 Early Tertiaries . 215 Igneous rocks 215 Granite 215 Volcanic rocks 215 Structure . 216 Ore deposits . 216 Hills from Randsbtirg east to Pilot Knob 216 Sedimentary rocks ■ 216 Arkoses ... 216 Igneous rocks 217. Ore deposits 217 Sierra Nevada 218 Sedimentary rocks 218 Cambrian 218 Carboniferous 219 Triassic... . 219 Jurassic _ 219 Igneous rocks 219 Structure 220 Index : 223 ILLUSTHATIONS. Page. Plate I. Geological reconnaissance map of Nevada south of the fortieth parallel, with adjacent California : In pocket II. Map showing position of geological reconnaissance map and chief data nsed in its compilation 15 III. ^-1, Jeff Davis or Wheeler Peak, Snake Range, from Robinson's ranch: B, North end of Schell Creek Range, from Antelope Range 26 IV. A, Snake Mountains north of Robinson's ranch; B, Antelope Range, east side BO V. A, East face of low mountain range west of Egan Range at Ely; B, Tertiary volcanic cone. Pancake Range, east side of Hot Creek 50 VI. ^-i, Rhyolite walls of Meadow Valley Canyon at Carson's ranch; B, Pliocene conglomerate in Meadow Valley Canyon at Kane Spring 140 VII. ^4, North scarp of Stonewall Mountain, Ralston Desert; i?. Pyra- mid Peak, Grapevine Range, from the head of Furnace Creek, . 183 VIII. Sketch structure section of Grapevine Range at Furnace Creek: A, Sketch cross section of the southern end of the Grapevine Range, at Furnace Creek; B, Sketch longitudinal section from the southern end of the Grapevine Range southward across Furnace Creek 194 Fig. 1. Sketch section 5 miles north of Hamilton across White Pine Range to the eastern edge of Long Valley Range fi6 2. Sketch section through White Pine Range at Hamilton at the junc- tion of White Pine and Long Valley ranges . _ _ 66 3. Generalized section on a line drawn a little north of east across Quinn Canyon and Grant ranges; at the north end of Quinn Canyon Range , but sou.th of the fault line _ 74 4. Sketch section of east front of Grant Range, taken 5 miles north of locality of fig. 3 75 5. Generalized sketch section of north end of Quinn Canyon Moun- tains 75 6. Generalized sketch cross section of Pancake Range at north side of pass at Twin Springs 80 7. Generalized sketch section across Hot Creek Range at Hot Creek _ . 88 8. Section of Eldorado Canyon , Pinenut Range 121 9. Sketch section of wall of arroyo in bottom of Eldorado Canyon, Pinenut Range 123 10. Generalized cross section of northern end of Mormon Range 186 11. Cross section of Muddy Range, after R. B. Rowe 138 13 14 ILLUSTKATIONS. Page. Fig. 12. Sketch section of east wall of Meadow Valley Canyon just south of Carson's ranch j4j 13. Sketch section of west wall of Meadow Valley Canyon at same local- ity as fig. 12 141 14. Sketch of east side of Meadow Valley Canyon near locality of fig- ures 13 and 13_ 142 15. Sketch section of south wall of Hackberry Canyon near junction with Meadow Valley Canyon I44 16. Sketch section of north wall of Meadow Valley Canyon 3 miles southwest of mouth of Hackberry Canyon I44 17. Sketch section on east wall of Meadow Valley Canyon from Kane Spring to Grapevine Spring I45 18. Sketch section of west wall of Meadow Valley Canyon at Grapevine Spring 14g 19. Sketch section of wall of Hackberry Canyon at Hackberry Spring. 147 20. Sketch section of southern end of Meadow Valley Range extended through the New Mountain Ridge 151 21. Generalized sketch cross section of Reveille Range near Reveille _ 162 22. Generalized sketch sections across Spring Motmtain Range . 176 23. Section showing great fault at Olcott Peak, after R. B. Rowe 177 24. Cross section of southern end of Spring Moiintain Range (east and west) , showing great fault several miles north of the point rep- resented in fig. 23 173 25. Cross section of Bird Spring Mountains (southern spur of Spring Mountain Range) , after R. B. Rowe I79 U. S. GEOLOGICAL SURVEY BULLETIN NO. 208 PL. II 121° 319° 117° IL5° 113° -<*> ^ San Cls meats 1/ 121° 110° 117° U5° 1L.3° l^ZAJP SHO^VH^G POSITION OF GEOLOGICAL IlECOT^lSIAISSAN^CE MAP ^AND CHIKF X)ATA.TJSED UST IT S C 0MT>rCATI01Sr Scale DESCRIPTIVE GEOLOGY OF NEYADA SOUTH OF THE FORTIETH PARALLEL AND ADJACENT PORTIONS OF CALIFORNIA. By JosiAH Edward Spurr. I N T R O D U C T I O N . The field work upon which the jiresent bulletin is based, so far as the writer's labors are concerned, was done in the summer and fall of 1899. After visiting the Wasatch Range to study briefly the Wasatch Paleozoic section, as determined by the Fortieth Parallel Survey, the writer proceeded to Eureka, in Nevada, and there spent two weeks in studjnng that section, the best and most complete yet discovered in the far West. Feeling finally ready for untried ground, the expedi- tion, consisting, besides the writer, of a teamster, a cook, and an assist- ant, left Eureka and proceeded southeastward to Hamilton, and then to Elj^ From Elj^ the route ran to Osceola in the Snake Creek Range, thence across that range and northward up Snake Valley to Pleasant Valley, where a westward course was again taken. Schellbourne and Cherry Creek, the latter in the Egan Range, were next visited, and thence the waj^ led northwestward to Ruby Lake, and so back to Eureka. During part of this journey some of the region which had been mapped by the Fortieth Parallel Survej^ was traversed, this route being purposely chosen so as to permit study in the field of the application of the Fortieth Parallel geologic section. After replenishing sup- plies at Eureka the expedition took the road southward to Hot Creek, and thence proceeded westward to Belmont. The country to Carson was then traversed, the more or less inactive mining camps of lone, Ellsworth, and Downieville and the Indian reservation at Walker Lake being passed. At Carson a short time was spent, and the famous Comstock lode and the southern end of the Virginia Range were visited. From Carson the route was southwestward past Wellington, Hawthorne, Sodaville, Columbus, and Silver Peak, to Lida. From Lida the course was again toward the east, and the State of Nevada was crossed again by way of tlie Ralston Desert, Twin Springs, and White River, to Pioche. From Pioche, Meadow Valley Canyon was followed southward to the Indian reservation at Moapa or West Point, not far from the Colorado, then, a turn to the west being made, the 15 16 GEOLOGY OF NEVADA SOUTH OF 40TH PAKALLEL. [bull. 208. State was crossed a third time, by way of Indian Springs and Pali- rumji Valley, into California. Funeral Range was crossed and Death Valley entered at Furnace Creels:. From here the expedition went southward, and, crossing the Panamint Range at Windy Gap, pro- ceeded by way of Granite Wells to Johannesburg. From Johannes- burg the party proceeded across the Mohave Desert, crossing the Santa Fe Railroad at Hinckley. Finally San Bernardino was readied, which was the end of the journey. This trip lasted about five months, and comprised over 2,000 miles of actual travel. The primary object of tlie expedition was to make the roughest kind of a general geologic map, such as might fill up the great gaps in the map of the western United States. It being the intention of the Sur- vey to publish a general geologic map of the United States on a scale of about 40 miles to the inch, no great amount of detail was advisable or possible. On account, also, of the rough and inaccurate manner in which much of the region of the western United States has been already mapped, it was not advisable to undertake to do any work of higher grade. In order to accomplish the style of mapping desired with as much economy of time and labor as possible, the writer determined to avoid anj^ duplication between his route and those already traveled by geolo- gists, and carefully planned his journeys with that end in view. On the north the area which he undertook to investigate was bounded by the geologic maps of the Fortieth Parallel Survey (atlas maps 4 and 5) ; on the east it was bounded by the geologic maps of the Wheeler sur- vey; and on the west chiefly by a reconnaissance map of the Sierra Nevada published by Mr. H. W. Turner in the Seventeenth Annual Report of the United States Geological Survey, Part I ; on the south there was no definite boundary. Within the area to be mapped, about the only important journey that had been made by a geologist had been accomplished by Mr. Gilbert in 1871, while with the Wheeler Topographic Survey. His route, with the other boundaries already mentioned, is shown on PI. II. The writer was able to so plan his route with reference to the work of Mr. Gilbert and to the maps which bounded the area that hardly any point in the region examined can be found which is more than 30 miles from a point of observation. This in any country would prob- ably be sufficient for a reconnaissance map on a scale of 40 miles to the inch, but in the Great Basin region of Nevada and California the conditions are especially favorable, so that a map can be made having far more value than in ordinary regions. The clear air, the lack of vegetation, and the general continuity of formations parallel with the north-south ranges all combine to make a reconnaissance more satis- factory than usual. The attitude of strata or a conspicuous formation maj" often be followed 15 or 20 miles along the front of a mountain, by the aid of a field glass, from a single point. SPURR] INTRODUCTION. 17 The foregoing explauation iudicates clearly euougli the character of the ma]3 aud the weight which should be placed upon it. The data along the lines of reconnaissance, often obtained on forced marches of 20 or 30 miles a day, are oftentimes meager and nnsatis- factor3^ Between the lines of actual travel the data are still less reliable, and a great deal of the mapping has been done simjply from inference. Thus it is probable that anyone examining closely the detail of the map will find it nearly all inaccurate, while one looking for the main principles will recognize the general correctness of the mapping and the value of the map as a pioneer. The inaccuracy of the map is unavoidably heightened by the lack of a suitable topographic base. The present base has been prepared in a very rough and unsatisfactory way, chiefly from the Wheeler and other early surveys. It is a source of regret to the author of the bul- letin that so rough a topographic map must be presented as the vehicle for his geologic information. Within the text of the bulletin an effort has been made to give clearly the known facts concerning the geology, whether obtained by the writer or previousl3\ Fidl credit is given to previous work, although it can not alwaj^s be given in the map compiled from this information. The chief sources, however, are shown on PL II." The writer has judged it most advisable to confine the text to descriptive matter. General results, especially those involving appli- cation of theory, have been withheld or published separately. Among these general results the author has published two papers on volcan- ism in the Journal of Geologj^ entitled The Succession and Relation of Lavas of the Great Basin Region (October-November, 1900), and Transitions of Texture in certain Tertiary Igneous Rocks of the Great Basin. A petrographic paper on Quartz-muscovite E'ock from Bel- mont, Nev., has been published in the American Journal of Science (November, 1900). A paper on the Origin and Structure of the Basin Ranges was read before the Geological Society of America at Albany, December, 1900. « After the above was written, and while the bulletin was in galley proof, new information was received as a result of the studies of Messrs. Weeks and Rowe, of the U S. Geological Survey.' The studies of Mr. Weeks were made in 1900; those of Mr. Rowe in 1900 and 1901, The results of these have been incorporated in the bulletin. Bull. 208—03 2 EXPLANATION OF FORMATION NAMES. The following is a brief explanation of formation names used in this work. Names are arranged alphabetically. Aubrey limestone and sandstone. — These names were applied by Messrs. Gilbert and Marvine in 1871 to formations in the Colorado Canyon region. The limestone lies above the sandstone and has a thickness of 820 feet on Kanab Ci-eek. At a few points in the top- most layer were found a group of shells suggesting the Permo-Carbon- iferous of the Mississippi Valley, indicating that the great Paleozoic lithologic change at this horizon marks the absolute close of the Carboniferous age. Lithologically the limestone is characterized by a great abundance of chert, which toward the top sometimes consti- tutes half the mass. Near the middle it is in some places interruj^ted by a belt of shale with gyi)suni. The underlying Aubrey sandstone series has a thickness in the Aubrey cliffs and along the Grand Canyon of about 1,000 feet. In every exjjosu re a portion of this bod}^ is massive and cross bedded and another portion soft and gypsiferous, but the order of these parts is not constant. The sandstones contain no fossils, but an intercalated limestone below the middle of the series at Canyon Creek bears famil- iar Coal Measures shells." Chuar series.— This name was introduced by Mr. C. D. Walcott in 1883 for a part of the LoAver Cambrian of the Grand Canyon region. Mr. Walcott divided the Grand Canyon group of Major Powell into a lower and an upper division, the Grand Canyon and the Chuar. In 1886 the reference to the Lower Cambrian was changed to pre-Cambrian. In 1890 these strata were referred to the Algonkian system. In 1894 Mr. Walcott again classified the Algonkian, dividing the Grand Canj^on series of this system into the upper (Chuar) series and the lower (Unkar) series. The Chuar is separated by an unconformity from the overlying Cambrian (Ton to series).* Diamond Peak quarizite. — -This name Avas given by Mr. Hague to the lowest lithologic member of the Carboniferous at Eureka, Nev. At this place the Diamond Peak quartzite consists of 3,000 feet of mas- sive gray and brown quartzites, with broAvn and green shales at the summit. It underlies 3,800 feet of heavy bedded, dark-blue and graj^ nU. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 177. 6 Fourteenth Ann. Kept. U. S. Geol. Survey, Part II, p. 506. 18 spuRR.] DESCRIPTIONS OF FORMATIONS. 19 Lower Coal Measures limestone, which contains intercalated beds of chert and argillaceous beds near the base. The Diamond Peak quartz- ite is not a persistent lithologic terrane, and is not recognizable Avith confidence at any great distance from tlie Enreka section. Es)neralda formation. — This name was ap^jlied by Mr. 11. W. Tur- ner" to Tertiary formations in the Silver Peak Range, in tlie west- ern part of Nevada. These deposits consist of sandstones, shales, volcanic tuffs, breccias, conglomerates, and great thicknesses of lacustrine marls. Coal beds and plant remains occur; also fossil shells and fish bones. From the evidence afforded b}^ these fossils, the age of the beds was broadly determined as late Eocene or early Miocene. Eureka quartzite. — This name was applied by Mr. Hague to the mid- dle of the three divisions of the Silurian in the Eureka district. This division here consists of 500 feet of compact vitreous quartzite, white or blue in color, and j)assing into rock of reddish tints near the base, with indistinct bedding. It overlies the Pogonip limestone, and is separated from the overlying Silurian Lone Mountain limestone by an unconformity. The Eureka quartzite appears to be one of the most persistent lithologic terranes of the Nevada Paleozoic. It has been recognized over a wide area. Grand Canyon groiqj. — The name Grand Canyon groux3 was given by Ma j. J. W. Powell to the strata in the Grand Canyon region beneath the Tonto sandstone and above the Grand Canyon schists. The latter were referred tentatively to the Eozoic, and the 10,000 feet of the Grand Canyon group to the Silurian. In 1883 Mr. C. D. Walcott referred Major Powell's Grand Canyon group to the Lower Cambrian and separated it into an upper and a lower division, the Grand Canyon and the Chuar. In 1886 these rocks were referred bj^ Mr. Walcott to the pre-Cambrian, and in 1890 to the Algonkian. In 1894 Mr. Wal- cott subdivided the Grand Canyon group of the Algonkian into the Chuar and the Unkar series. The Grand Canyon group is separated by an unconformity from the overlying Cambrian (Tonto sandstone), and by a great unconformity from the underlying Vishnu series of schists. Hamhiirg limestone a7id shale. — The Hamburg limestone and shale are the uppermost divisions of the Cambrian as defined by Mr. Hague in the Eureka district, Nevada. The Hamburg shale lies at the very top and consists of 350 feet of yellow argillaceous shale containing layers of chert nodules, especially near the top. The underlying Hamburg limestone consists of 1,200 feet of dark-gray granular lime- stone, with only slight traces of bedding. The Hamburg shale is characterized by well-developed Upper Cambrian fauna.* a Am. Geol., Vol. XXV, p. 168. & Second Ann. Bept. U. S, Geol. Survey, p. 37; Third Ann. Kept., p. 255. 20 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.308. Huitiboldt series. — This name was applied by King"^' to a series of loose, friable Tertiar}^ rocks, carrying very recent fresh-water niol- lusks. This series is found at intervals all over the northern portion of the Great Basin region, from the Sierra Nevada into Utah. Mr. King regard-ed all these beds, which from their fossils were referred to the late Pliocene, as lake deposits and as representing the sedi- ment of a single lake out of which the numerous lofty mountain masses rose in a complicated system of islands. Koipato formation. — This name was applied by Mr. King* to one of the two chief divisions of the Triassic in western Nevada. He describes the Koipato as made up of siliceous and argillaceous beds, whose chemical peculiaritj^ is the almost total absence of soda and lime and the high percentage of alumina and potash. This series has an observable thickness of about 6,000 feet, with an unknown quan- tity to be added for the unseen beds at the bottom. Tlie Koipato is overlain by the Triassic Star Peak series. Lone Mou7itai7i limestone. — This name was given by Mr. Hague to the uppermost division of the Silurian in the Eureka district. It consists of 1,800 feet of strata. At the base are black gritty beds passing into light-gray siliceous rocks with all traces of bedding obliterated. There are Trenton fossils at the base and Halysites in the upper portion. The formation is separated from the underlying Silurian Eureka quartzite by an unconformity, and is overlain con- formably by the Devonian Nevada limestone. Nevada limestone. — The Nevada limestone, as defined b^'' Mr. Hague,'' is the lower member of the Devonian series at Eureka. It consists of 6,000 feet of limestone. The lower horizons are indis- tinctly bedded, with saccharoidal texture and gray color, passing up into distinctly bedded strata, reddish brown and graj^^ in color, fre- quently finely striped, ijroducing a variegated appearance. The upper horizons are massive, well bedded, bluish black in color, and highly fossiliferous. The Nevada limestone overlies the Silurian Lone Mountain limestone at Eureka and is overlain by the Devonian White Pine shale. Ogden quartzite. — This term was applied by King'^ to a sheet of siliceous sediment, in general compacted into a quartzite. Mr. King stated that this formation had a remarkable evenness over all the Paleozoic area west of and including the Wasatch. In its typical locality, Ogden Canyon, AVasatch Range, it was stated to be 1,200 or 1,400 feet thick; at Cottonwood Canyon 1,000 feet, and in middle Nevada from 800 to 900 feet. In Ogden Canyon it is bounded at the top and bottom b}^ thin beds of greenish-gray argillites; and n U. S. Geol. Expl Fortieth Par., Vol. I, p. 434. blbid.,p. 346. c Third Ann. Rept. U. S. Geol. Survey, p. 2ba. rtOp. cit., p. 234. SPURR] DESCKIPTIONS OF FORMATIONS. 21 about the middle of the qnartzite is a thin bed of white, slightly silice- ous marble. No fossils were found in this formation, but it was referred to the Devonian, since it was found to overlie the Pogonip limestone, which contains Lower Helderberg fossils, and is overlain by the Wasatch limestone, whose basal beds contain Upper Helder- berg forms. Pogonip formation. — King'* described the Pogonip limestone in middle Nevada, in the regions of White Pine, Eureka, Pinyon, and Roberts Peak ranges, as being Cambrian in the lower half and con- taining Silurian fossils in its upper 2,000 feet. In the Eureka sec- tion, the term Pogonip was limited by Mr. Hague ^ to the Silurian portion of the series, which consists of 2,700 feet of interstratified limestone and argillites, with arenaceous beds at the base> These rocks pass into pure, fine-grained limestone of a bluish-gray color, distinctly bedded. They are highly fossiliferous. The Pogonip lime- stone is the lowest member of the Silurian of the Eui'eka section. - It overlies the topmost member of the Cambrian, the Hamburg shale, conformably, and is conformably overlain by the Silurian Eureka qnartzite. Prospect Mountain limestone and quartziie. — These names were given by Mr. Hague ^ to the two lowest divisions of the Cambrian sec- tion at Eureka, Nev. The Prospect Mountain qnartzite is the lowest and consists of 1,500 feet of bedded brownish- white quartzites, weath- ering dark brown but Avhiter near the summit. The quartzites contain intercalated thin laj^ers of arenaceous shales, and are ferruginous near the base. The qnartzite is overlain by the Prospect Mountain limestone, which consists of 3,050 feet of gray, compact limestone of rather light shade, traversed by thin seams of calcite. It has very imperfect bed- ding iDlanes. The upper portion of the Prospect Mountain quartzites is characterized by the Olenellus or Lower Cambrian fauna, and the Prospect Mountain limestone by the Middle Cambrian fauna of the Rocky Mountain section. Red Wall limestone.- — This name was applied by Messrs. Gilbert and Marvine '^ to a heavy Carboniferous limestone in the Grand Can- yon region. This limestone has a gray color on fresh fracture, but shows a red rust on weather-stained cliffs. It is generally heavy bedded to massive. At the top sandstone alternates with limestone for from 200 to 500 feet. Through its lower half the limestone is interrupted by occasional shaly bands. The average total thickness is 2,500 feet. Fossils are abundant near the top but rare in the lower part. The upper portion contains Coal Measures fossils. The lowest aU. S. Geol. Expl. Fortieth Par., Vol. I, p. 232. b Third Ann. Rept. U. S. Geol. Survey, p. 255. cU. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 178. 22 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. fossils were obtained just below the middle of the series, and were doubtfully referred to the Lower Carboniferous. Secret Canyon shale. — This name was applied bj'- Mr. Hague « to a division of the Cambrian in the Eureka district overlying the Prospect Mountain limestone and underlying the Hambiirg lime- stone. It consists of 1,G00 feet of yellow and gray argillaceous shales, passing into shaly limestone. This formation is characterized by a fauna that may be referred to the upper portion of the Middle Cambrian. Star Peak formation. — This name was applied by Mr. King'' to the uppermost of the two great divisions of the Triassic of western Nevada. The series consists of 10,000 feet of strata, made up of an alternation of three great limestone zones and three interposed quartz- ite zones. The upper two quartzites represent moderately pure sili- ceous sediment, while the lower quartzite closely follows the physical and chemical peculiarities of the underlying Triassic Koipato series. The fossils of these limestones are marvelously like the St. Cassian and Hallstadt of the Austrian Alps. Directly overlying the upper- most Star Peak quartzite is a limestone carrying Lower Jurassic or Liassic forms, and succeeded upward by an immense series of argil- lites of unknown thickness. Tonto shale and sandstone. — The name Tonto was applied by Mr. G. K. Gilbert « in 1874 to a series of sandstones and shales lying l3etween the subjacent granite and the superjacent limestones wJiich occur at the mouth of the Grand Canyon in Arizona. He considers the formation of Primordial age, and it has been since found to con- tain an Upper Cambrian fauna. ^ Truckee formation. — Mr. King« proposed the name Pah-Ute Lake for a fresh-water Miocene lake, which is regarded as extending from the region of the Columbia River, and perhaps still farther north, far south through Oregon and Nevada into California. To the beds of this lake in the fortieth parallel area lie gave the name of Truckee Miocene. They are made up of 150 feet or less of detrital rocks and gritty sandstones, with some conglomerate. Above these lie about 250 feet of palagonite tuff. Above this is 250 to 300 feet and more of infusorial silica, followed by 120 feet of detrital sandy rocks, contain- ing also infusorial silica. Above these comes 60 feet of fresh-water limestone, which is succeeded upward by 250 feet of detrital grits; and the latter give away to an enormous formation of volcanic tuffs. In Nevada the thickness of these volcanic muds is 2,000 or 3,000 feet; in Oregon it is even more. a Third Ann. Rept. U. S. Geol. Sui-vey, p. 355. b U. S. Geol. Expl. Fortieth Par., Vol. I, p. 346. c Bull. Washington Philos. Soc, Vol. I, p. 109. d C. D. Walcott, Bull. U. S. Geol. Survey No. 81, p. 245. e Op, cit., p. 454. gptJRR.] DESCEIPTIONS OF FOEMATIONS. 23 Unkar formation. — This has alreadj- been mentioned, under the headings Grand Canyon and Chuar, as the lowest division of the Grand Canyon group of the Algonkian in the Grand Canyon section. It is overlain conformably by the Chuar, and separated below by a great unconformity from the Vishnu series. Wasatch limestone. — The term was applied by King" to an enor- mous bodj^ of limestone seen in the Wasatch and farther west, but not to the east. He describes it as a single body of limestone about 7,000 feet in thickness, holding its enormous volume with remarkable evenness wherever observed over Utah and Nevada. It is underlain by the Ogden quartzite, from which it is lithologically sharply distin- guished. Above, it passes into the great Weber quartzite, but there is an alternation of sandstone and limestone beds at this transition and the thickness of these intercalated beds is very variable, reach- ing sometimes about 1,000 feet. The lower 1,400 feet of the Wasatch limestone was regarded as Devonian. Above this is 300 or 400 feet of dark, heavy limestones carrying fossils resembling those of the Waverly group, but which perhaps are closer to the Devonian. Directly above these are 400 or 500 feet of dark beds carrying Lower Carboniferous fauna, and above these the upper 4,500 feet of the limestone is characterized by abun- dant Coal Measures fossils. The term Wasatch was not retained in the Eureka section,^ the Devonian and Carboniferous being subdivided into various forma- tions. However, these lithologic subdivisions are not readily recog- nizable at many other points in Nevada, and the old term is often convenient. Weber conglomerate. — Mr. King^ described the Weber quartzite as a body of indurated sandstone and quartzite carrying occasional sheets of conglomerate, interposed between two bodies of Coal Meas- ures limestone. He described .it as obtaining a thickness of 2,000 feet in the Wasatch, 8,000 feet in the Oquirrh, and probably more in middle California. This formation overlies the Wasatch limestone and underlies the Upper Coal Measures limestone. The same formation was recognized by Mr, Hague ^^ at Eureka, where it is underlain by the Lower Coal Measures limestone and over- lain by the Upper Coal Measures limestone. Its thickness at Eureka, however, is only 2,000 feet. Here it consists of coarse and fine con- glomerates, with angular fragments of chert and layers of reddish- yellow sandstone. White Pine shale. — This term was a^jplied by Mr. Hague '^ to the aJJ. S. Geol. Expl. Fortieth Par., Vol I, pp. 335-239. 6 Arnold Hague, Mon. U. S. Geol. Survey, Vol. XX, p. 13. cQp. cit., p. 240. dLoc. cit. 24 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. uppermost of the lithologic divisions of the Devonian in the Eureka district. It consists of 2,000 feet of black argillaceous shales, more or less arenaceous, with intercalations of red and reddish-brown friable sandstone, changing rapidly with the locality. The beds contain plant impressions. The formation is underlain by the Devonian Nevada limestone and overlain by the Carboniferous Diamond Peak quartzite. These lithologic subdivisions seem to change rapidly as one goes away from the Eureka district, and have not often been certainly identified. CHAPTER T RAI^GES OF EAST-CENTRAI. KT5VADA. SNAKE RANGE. The Snake Range lies next east of the Schell Creek Range and for the most part just west of the Nevada-Utah line. It is the most eonspicnous range between the Wasatch and the Humboldt. The northern end of the range has been variously called the Deep Creek Mountains or the Ibenpah Mountains, while just south of this part of the range a transverse ridge has been called the Kern Mountains; but here they will all be included under the general name Snake Range. The range, as thus defined, extends from about latitude 40° 15' about 135 miles in a direction a little west of south. At its southern end it runs into a group of irregular mountains, probably in large part vol- canic, of which certain portions go by the name of the Cedar Moun- tains, and the Piiion Mountains of Lincoln County. TOPOGRAPHY. The relief of the Snake Range is in general great. The mountains are divided into irregular ridges which are broken and separated by transverse east- west gaps. Bj^ two such gaps the so-called Kern Mountains are separated from the rest of the range, and a similar but lower gap occurs just north of Wheeler or Jeff Davis Peak. This peak has the highest elevation of any between the Sierra Nevada and the Wasatch, attaining over 12,000 feet (PI. HI, A). Directly south of this the mountains decrease rapidlj' in height and pass into the low volcanic peaks above mentioned. Some of the erosion forms are interesting. On the east side of the range, between Wheeler Peak and the Kern Mountains, a number of springs furnish continual streams. At the mouths of the gulches from which such streams flow the Pleistocene wash which covers the base of the mountains has been lowered fully 500 feet below the wash on both sides, and the stream flows through this deposit between steep banks 40 feet high. Where near-by gulches which do not con- tain any continual streams join the same detrital apron, the reverse is the case, the gulches being fronted by huge alluvial fans higher than the rest of the i)lateau. Considering the gulches formed b}^ these continual streams and comparing them with the neighboring gulches which do not contain springs, we find a strong contrast. Smith Creek, for examj)le, is 25 26 GEOLOGY OF JSTEVADA SOUTH OF 40TH PARALLEL. [buli..208. a spring flowing in the bottom of a magnificent narrow canyon, bounded by perpendicular walls 2,000 or 2,500 feet high. In these walls are a number of large holes or caves in the limestones, which evidently represent the former courses of the same spring that now emerges in the gulch bottom. From the distribution of these caves it appears that the spring has been flowing during all the time that the canyon has been eroding and that its former underground courses have been exposed by the down cutting. The adjacent gulches, which do not continually contain running water, have V-shaped valleys with- out box canyons, and are much shallower. In this canyon are small working mines. ARCHEAN ROCKS. Howell found fragments of granite in the wash which came down from Wheeler Peak, and regarded this as Archean, underlying the undoubtedly Cambrian quartzite. Farther north, on the east face of the mountain, and on the north side of the gap which runs trans- versely across the range north of Wheeler Peak,- the writer found abundant schistose granite in the drift and in one locality in place. Where it was found in place it seemed to lie beneath limestones which are probably Cambrian, with no intervening quartzite. Farther north, also on the eastern side of the range, one finds continually huge blocks of schistose granite mingled with the blocks of schistose Cambrian quartzite. Upon the north side of the Kern Mountains granite is found in contact with the schistose Cambrian quartzite and also with the overlying metamorphic limestones. The central portion of the Kern Mountains is made up of this granite, with the Cambrian rocks on the flanks. A sjpecimen examined microscopically proved to be a biotite-muscovite-granite, approaching alaskite. On the borders of the granitic mass are found siliceous granitic dikes, which cut the Cambrian quartzite-schists. At one locality, which is on the south- west side of Pleasant Valley and near the State line, is found a broad belt of confused alaskite dikes showing a tendency to change into a muscovite-biotite-granite on the one hand and into large quartz veins on the other. Howell'* notes that at the head of Deep Creek, only a few miles north of Pleasant Valley, the erosion of the creek has laid bare gran- ite underlying the quartzite and limestone. From here northward to Uiyabi Pass, not far from the northern end of the range, he notes that the base of the range is granite, overlain and flanked on the west by quartzite and limestone. From these evidences it would seem that the limestones and over- lying quartzites which form the base of the stratifled series in the Snake Range, and which will be presently shown to be Cambrian, are ordinarily underlain by granite. But in at least one locality similar "U. S. Geog. Surv. W. One Hundredth Mer., Vol., Ill, p. 242. U. S. GEOLOGICAL SURVEY BULLETIN NO. 203 PL. Ill A. JEFF DAVIS OR WHEELER PEAK, SNAKE RANGE, FROM ROBINSON'S RANCH. li. NORTH END OF SCHELL CREEK RANGE, FROM ANTELOPE RANG: Showing also the Tertiary and Pleistocene valleys between the two ranges. sPURR.] SNAKE RANGE. 27 granitic rock is locally intrusive into the Cambrian strata, and the same has been suspected in other places. From the fact, however, that the intrusive phenomena are of minor importance, and also from the circumstance that where the Cambrian quartzite is schistose the underlying granite also shows signs of movement, the writer inclines to the belief that the granite as a whole is really Archean and is the basement upon which the Cambrian quartzites were laid down. So thick a series of quartzites (amounting to several thousand feet) naturally suggests a granitic land mass as their source. As regards the occasional intrusive phenomena, it is possible that these represent occasional outbursts of molten rock which found its way from the lower and more heated regions up through the crust of hard Archean granite and into the overljdng Cambrian, being intrusive into the Upper Archean as well as into the quartzites, although belonging prac- ticallj" to the same body as the basement granite. The writer would suggest that this explanation may ]Dossibly apply to Big Cottonwood Canj^on, in the Wasatch, near Salt Lake City, where the granite was originally believed to be Archean, but where later observers have noted intrusive phenomena.* SEDIMENTARY ROCKS. CAMBRIAN. In the southern part of the range, at Wheeler Peak, there are heavy quartzites dipping in all directions, forming a gentle quaquaversal. Howell^ notes the same quartzites for some distance south of the iDeak, overlain by heavj^ bluish-gray limestones. He estimates the lime- stones as 4,000 to 5,000 feet thick, and the underlying quartzite at not less than 1,000 feet. North of Wheeler Peak, at the mining camp at Osceola, the writer observed these quartzites, and found on the mountain just south of the camp about 500 feet of pure white quartzite underlain by about 2,000 feet of massive gray quartzite, with some silvery slate. At Osceola there is an east-west fault which brings together a massive brown craggy- weathering quartzite on the north side and the silvery slate with quartzite bands on the south: Above the quartzite, one mile east of Osceola, there is a high bluff of dark-blue frosty lustered silice- ous limestone with indistinct, probably organic, markings, similar to the limestones just west of here, in the Schell Creek Range. About a mile farther east the slight westerly dip of the limestones brings up the same underlying silvery slates as were noted in the neighborhood of Osceola and also in the Schell Creek section at the same horizon. The limestones in the neighborhood of Osceola were estimated at 1,000 feet thick, while the slates, as exposed in the Schell Creek sec- tion, were roughly estimated at from 4,000 to 5,000 feet. A short oC. E. Van Hise, Correlation Papers, Archean and Algonkian: Bull. U. S. Geol. Survey No. 86, p. 289. &U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 241. 28 aEOLOGY Oli' NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. distance farther east the slates are underlain by 300 feet of brown quartzite like that at Osceola, below which comes 600 feet of gray quartzite. The following observations have been directly communicated to the writer by Mr. F. B. Weeks, who made an extended trip in the Great Basin region in the summer of 1900: A few hundred feet below the summit of the ridge south of Osceola fossils were found in the limestone and have been determined by Mr. Walcott as Lower Cambrian. About 8 miles northeast of Osceola the center of the range is occupied by hard and massive drab and blue limestones, in which fossils collected at two localities have been determined by Mr. Walcott to be Middle Cambrian forms. These Cam- brian limestones are succeeded by Ordovician limestones. We have, then, in the neighborhood of Osceola a section of sedimen- tary rocks resting upon the basal granite and consisting of at least 2,500 feet of quartzites, succeeded by a thickness of silvery, somewhat micaceous slates of uncertain but iDrobably considerable thickness, and these by at least a thousand feet of metamorphic limestones. The section is identical with that just west of here, in the Schell Creek Range. About 20 to 25 miles south of Wheeler Peak Cambrian limestones, overlain by Ordovician limestones, Avere also observed by Mr. Weeks. All along the eastern side of the Snake Range, north of Wheeler Peak, is found the same section, although the overlying silvery slates often become more quartzitic and pass into quartzite-schists. Just north of the east- west gap crossing the range north of Wheeler Peak a series of 2,500 to 3,000 feet of craggy-weathering brown or black considerably altered limestones, reticulated by many veins and highly jointed, was gone through. In this limestone no fossils were seen, but above it is found limestone with Coal Measures fossils. The lower limestone is believed to be in part Cambrian, for below it was found a belt of about 200 feet of black shale, in which a number of fossils were collected, which were determined by Mr. C. D. Walcott to be Cambrian. Below this shale comes a peculiar 50-foot bed of white marble, banded with gray, and beneath this upward of 1,500 feet of highly schistose quartzite, producing the effect of a silvery slate. From here north to the transverse gap which cuts across the range south of the so-called Kern Mountains, one finds almost continuously the same quartzite-schists at the bottom of the section, sometimes nearly approaching the condition of a mica-schist. Above this come heavy bedded limestones, which weather brown, and which carry indistinct and indeterminable fossil remains. Midway between the northern end of the main portion of the Snake Range, south of the Kern Mountains, and the Kern Mountains themselves, the same metamorphic limestone was found in a butte. From observations all along this face of the range the thickness of the metamorphic limestone was estimated at about 5,000 feet. A spec- spuRR.] SNAKE EA.NGE. 29 imen of the limestone examiued aj)peass, occurs dark-blue limy shale, containing Cambrian fossils, as determined by Mr. C. D. Walcott. This shale is several hundred feet thick and contains a bed of fine- grained brown-weathering quartzite 100 feet thick. Similar fossils are found above and below the quartzite. Beneath the shale comes a well-bedded limestone. In the west-facing scarp of the mountain, directly north of the pass as seen from Scliellbourne, the section examined may be seen finely exposed. From stratigraphic evidence the writer would be inclined to correlate the uppermost limestone with tlie Hamburg formation of Eureka, the shales with the Secret Canyon formation, and the lower limestones with the Prospect Mountain limestone. An estimated section of the mountains here is as follows : Section nea.r Schellhourne. Feet. Hamburg limestone 600 Secret Canyon shale _. 600 Prospect Mountain limestone 1, 800 Neither the top nor the bottom of the section was observed. About 30 miles south of Whites Peak and Piermont the writer crossed the Schell Creek Range along the main road between Ely and Osceola. On the east side of the summit (which is not high at this point) limestone carrying abundant Carboniferous fossils appears to abut against massive dark-blue metamorphosed limestone, reticulated with calcite veins, and associated with beds of marble. Immediatelj^ below the metamorphic limestone beds is a ferruginous and micaceous slate seam, contorted and containing veins of quartzite and calcite. This limestone and underlying schistose slates constitute the whole eastern part of the range. 1^0 fossils were found at this point, but the beds are probably to be correlated with the Cambrian limestones and underlving shales at 40 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. Whites Peak, at Ruby Hill, and Schellbourne. The succession and the general chai'acter of the rocks are also similar to those of the Cambrian limestones and shales in the Highland Range in the vicin- ity of Pioche and in the Snake Range directly east of here, in both of which localities Cambrian fossils have been found. On the west side of the range, north of the locality just described and directly east of Ely in the Egan Range, the ridge which flanks the main Schell Creek Range on the east has along its crest what appears from a distance to be the white Eureka quartzite of the Silurian, dipping west at a constant angle of about 30°. Between this ridge and the main range there is a parallel depression which runs along the axis of an anticline, for to the east of it the strata have an easterly dip of from 20° to 30°. On the ridge itself there comes in below the Eureka quartzite strata resembling the thick, comparativelj' soft limestones of the Pogonip formation, and beneath this, in the bottom of the valley, are exposed massive gray limestones, which are perhaps Cambrian. These Cambrian and Silurian rocks do not extend south past the end of the ridge which forms the western high limb of the anticline, but are replaced to the south ^^y the Devonian, tilie two regions being appar- ently separated by a heavy east-west fault. Mr. Howell'* has described the rocks at the southern end of the Schell Creek Range. He notes that at Patterson a heavy bed of quartzite is exposed, dipping about 45° ESE. A few miles to the north this is covered conformabl}^ by bluish-gray limestone. IsTo fos- sil remains sufficient for determination were found, but the limestone was correlated on lithologic grounds with the su^jposedly Carbonifer- ous limestones of the Snake Range and the Highland Range. Inas- much as at least the southern portion of the Highland Range consists of Cambrian limestones, which were classed by Mr. Howell as Carbon- iferous, but subsequently definitelj^ determined as Cambrian, and since the same Cambrian series occurs in the Snake Range, it seems likely that these rocks may also be Cambrian.* At the north end of the Highland Range, just south of Patterson, Mr. Howell found Carboniferous limestone well characterized by fossils. At Bristol, on the west side of the range, and about 30 miles south of Patterson, Mr. Howell noted quartzite at the base, while the whole upper portion was highly metamorphic limestone. This section, so far as it goes, accords with the Cambrian section of the southern end of the range, as will be mentioned later. Mr. Walcott '' noted on the western side of the range, at the same locality as just mentioned, the occurrence of the Eureka quartzite. It is possible that this is the same quartzite mentioned by Mr. Howell. «U. S. Geog. Surv. W. One Hundredth Mer., Vol. HI. x> 2'i2. I) Subsequent to tho writing of this Mr. F. B. Weeks collected Cambrian fossils near Patterson, in these limestones, above the quartzites. e Bull. U.S. Geol. Survey No. 30, p. 36. • SPURR.] SCHELL CREEK AND HIGHLAND RANGES. 41 The writer passed only a few miles from Bristol, proceeding- from Coyote Spring over Stami^ede Gap, and he also mapped the Silurian as extending across the valley to Bristol, and indicated in liis notes the probable occui'rence of the Eureka quartzite. At Stampede Gap the range, with the exception of some ver}^ low foothills at the western base, which will be referred to later as prob- ably Devonian or Silurian, is composed of about 800 feet of mingled limestone and slate overlain by about 1,400 feet of massive limestone containing siliceous beds. Some of these upper limestones carry indistinct and indeterminable organic remains. A mottled structure, seeming to indicate the former presence of coral remains in the now altered rock, is common, being the same structure as observed in the Cambrian rocks of the Schell Creek Range, described above as occur- ring about 30 miles south of Piermont. In the limestones at both localities metainorphism has caused the same peculiar pitted appear- ance which results from the segregation of metamorphic minerals. In the Highland Range, about 4 miles south of Stampede Gap and about the same distance southwest from Pioche, the entire range appears to be of Cambrian strata, and Mr. Walcott" has measured the following section: Section in High Ian d Range 4 miles south of Stampede Gaj). Feet. 1 . Quartzite 350 2. Limestone and shales, argillaceous and arenaceous 1 1 , 450 3. Massive limestone 3, 000 Total 4,800 The fossils which he collected at various points correlated this sec- tion with the Cambrian at Eureka, the Itasal quartzite corresponding to the Prospect Mountain quartzite. In the Highland Range, south of Bennetts Spring, the writer has noted the probable continuation of the Cambrian section for a dis- tance of 5 or 6 miles at the very least, the section being substantially the same as between Bennetts Spring and Stampede Gap. From the eastern base of the Highland Range abundant quantities of brown quartzite, probably representing the basal Cambrian quartzite of Mr. Walcott's section, come down into the vallej^ drift. This quartzite is probabh^ overlain by the Cambrian limestone, for the strata appear horizontal on the east side of the Highland Range throughout prac- tically its whole length. At Pioche Mr. Howell* noted 400 feet of highly metamorphic blue- gray limestone, and below this about .400 feet of shales, which yielded abundant Cambrian fossils. Below these shales is an unknown thick- ness of quartzite. He correlated this quartzite with the Cambrian quartzites of the Snake and Wasatch ranges. Mr. Walcott* has also «BuU. U. S. Geol. Survey No. 30, p. 34. b\J. S. Geog. Sm-v. W. One Hundredth Mer., Vol III, p. 242. 42 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. studied the Cambrian section at Pioche and finds a tliiclvness of the basal quartzite of 1,200 feet on the west face of the Elj^ Range, a few miles to the west of the town of Pioche. Mining operations have thrown out large masses of shales carrying Cambrian fossils, which Mr. Walcott * has described and correlated with a bed of the Highland Range section. Similar fossils were also collected at the same locality hy the writer. This horizon is well up in the shaly limestone which overlies the basal quartzite. Three or 4 miles southeast of Pioche, along the road to Panaca, what is probablj^ tlie basal quartzite is slightly exposed, immediately overlain by the shales. From these shales Mr. Walcott collected a number of Cambrian fossils. The writer also collected fossils from this point. SILURIAN. In the western face of the Schell Creek Range, just east of EI3' in the Egan Range, what is perhaps the Silurian Eureka quartzite appears, forming the crest of a minor ridge, flanking to the west the main Schell Creek Range. The quartzite dips to the west about 30" and is underlain by what appears to be the Pogonip formation. No fossils were collected. The Silurian rocks above described are probably cut off to the south by an east- west fault, for thej^ are succeeded bj^ Devonian strata. Mr. F. B. Weeks ^ found, in 1900, that, about 10 miles nortli of the road leading from Osceola to Ely, the Cambrian beds on the north- east are separated from Ordovician beds on the southwest b}^ a heavy fault. In these Ordovician beds the following fossils, determined by Professor Ulrich, were collected : Orthis (related to O. bellariigosa)-. Dalraaiiella (near perveta). Dalmanella (near emacerata). Modiolodon sp. nndet. Ischyrodonta sp. tindet. Cyrtodonta ? sp. tindet. Mackirea (cf. subannulata Walcott). Gyronema (near semicarinatum). Metoptoma sp. iindet. Endoceras (1). Endoceras (2). Leperditia (near fabulites). Leperditella. Leperditella (with ventral swelling). Sclnnidtella n. sp. (near crassimarginata). Aparcliites sp. nndet. Olenus ? sp. undet. (1). Olenus ? sp. iindet. (2). Asaphns. Pygidinm. sp. tindet. « Bull. U. S. Geol. Snrv. No. 30, p. 36. f Personal commimication to the writer. Blbid., pp. 34, 35. spuRR] SCHELL CREEK AND HIGHLAND EANGES. 43 Another lot was as follows: Asaphus (related to Megalaspis belemnuras White). Two species of trilobites related to Symphysurus goldfussi Walcott. Leperditella (related to L. inflata). Undet. ostracod (? related to Octonaria). Silurian rocks do not appear, so far as yet observed, until the neigh- borhood of Bristol, where the Eureka quartzite Avas observed by Mr. Walcott. The writer also has observed probable Silurian rocks, con- stituting low hills, which connect the Highland Range, in th.e neigh- borhood of Bristol, with the irregular ridges lying between the Egan and Pahroc ranges. Farther south Mr. Walcott " has noted the Eureka quartzite on the west side of the Highland Range, in a hill north of the road leading from Bennetts Spring to Hiko. At this point fossils ai'e very abundant. DEVONIAN. At the western base of the Highland Range, at Stampede Gap, highly fossiliferous strata were observed, probably separated from the Cambrian strata which form the mass of the range bj^ a heavy north- south fault. No fossils were collected, but from the stratigraphy it seems possible that these are the continuation of rocks in the neigh- borhood of Coyote Spring, at the northern end of the Pahroc Range, just west from Stampede Gap, which are Devonian. On the western side of the range, north of the road which crosses it between Ely and Osceola, the writer found dark-blue to gray-blue, often shaly limestone filled with calcite seams. From one horizon in this limestone he collected the following Devonian fossils, which were determined by Dr. George H. Girty: Stromatoporoid coral, Sjjirifer utaJiensis, and Amhocadia umbonata. These Devonian strata are apparentl^^ separated from Silurian and Cambrian rocks farther north by an east- west fault. CARBONIFEROUS. The western half of the Schell Creek Range, where it was crossed qn the road between Ely and Osceola, about 20 miles southeast of Ely, is chiefly composed of Carboniferous rocks. Thej" consist mostly of dark-blue, gray-blue, and often shaly limestones, with occasional brown quartzite seams. Some of the beds are semicrystalline. The series throughout is highl}^ fossiliferous. Just after the road enters the range Upper Carboniferous fossils were collected. They wore determined by Dr. George H. Girty, as follows: Zaphrentis sp., Productus sp., Spirifer rockymontanus, ^ Semimda sp. «BuU. U. S. Geol. Survey No. 30, p. 36. 44 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. A mile east of the above-mentioned locality the following Upper Carboniferous fossils were collected : Orbiculoidea missoiiriensis. Prodiictiis infiattis? Marginif era imiricata. T Cleiothyris orbicularis. Seminula snbtilita. ' Rhombopora lepidodendroides. All these Carboniferous rocks dij) to the east 20° or 30°, and appar- ently abut directly against the Cambrian on the east. Near the northern end of the Highland Range, 3 or -4 miles south of Patterson, Mr. Howell'^' has noted 2,000 feet of limestone containing well-marked Carboniferous fossils. IGNEOUS ROCKS. In the vicinity of Schellbourne the whole eastern part of the Schell Creek Range is covered by basic lava, and this also overflows to the western part of the range, covering up in patches the stratified Cam- brian rocks. This lava is in general a pyroxene-aleutite. According to Mr. Emmons,* the extreme northern portion of the range is entirely covered by rhyolite. In the vicinity of Schellbourne the writer found, underlying the basic lava, a few feet of white biotite-rhj^olite. On the western side of the Highland Range, 5 or 6 miles south of its northern end, Mr. Howell '^ has reported lava. Still farther south, at Stampede Gap, the writer observed a small area of rhyolite in the vallej^ at the western base of the mountain. Mr. Gilbert '^^ has noted in Ruby Hill Canj'on, a few miles south of Schellbourne, siliceous dikes cutting the Cambrian limestones. STRUCTURE. On the west side of Schell Creek Range, just east of Ely, a conspic- uous anticline was observed, trending parallel to the crest of the main range. The axis of this anticline is occupied by a valle}^, and the western limb is marked by a minor north-south ridge running from about the latitude of Ely northward to the neighborhood of Schell- bourne, The rocks exposed in this anticlinal fold are probably Silu- rian. To the south the fold, and at the same time the ridge in which aU. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 243. b U. S. Geol. Expl. Fortieth Par., Vol. II, p. 486. c Op. cit., p. 243. d\J. S. Geog. Sui-vey W. One Hundredth Mer., Vol. Ill, p 31. spuRR] SCHELL CREEK AND HIGHLAND RANGES. 45 its western limb is exhibited, are api3arently cut off by an east-west fault, while on the north the rocks of the fold pass under the Pleisto- cene valley detritus. About 10 miles south of the southern end of the minor ridges above mentioned what aj)pears to be the continua- tion of the same anticlinal fold is exhibited in the foothills on the west side of the range. Still farther south the general strike of the rocks changes from south to soutliAvest, and this anticlinal fold prob- ably passes over into the southern end of the Egan Range, Avhere-a series of folds was observed, one of which is perhaps identical with it. Farther south again there is probably another synclinal fold, whicli also passes over into the Egan Range on account of its south- westerly strike. This is probably followed by an anticlinal fold, such as HowelP' has described, at the extreme southern end of the range, where the rocks dip east-southeast. Still farther south the several folds which are found in the ridges forming the southern extremity of the Egan Range are probably continuous across the intervening valley to the Highland Range. The Cambrian rocks, which form the greater iDart of the eastern portion of the Schell Creek and Highland ranges, are also folded. At Schellbourne the rocks seemed to the writer to dip in general to the east, although the attitude could not be certainly made out. Farther south, at Whites Peak, Mr. Gilbert^ found the Cambrian rocks dipping to the west at an angle of about 20°. Still farther south, Avhere the writer observed the Cambrian rocks in crossing the range between Ely and Osceola, he found the folding complicated and the faulting considerable. In the Highland Range the folds in the Cambrian rocks appear to be gentle and of no great extent. Those that were observed Avere mostly transverse to the range, and in general the disposition of the horizons did not vary greatlj^ from what they would have been had they been horizontal. FAULTING. Although no careful examination has been made, the stratigraphy indicates the existence of important faults in the Schell Creek and Highland ranges. These probably belong to two chief systems — one north and south and one east and west. On the road which crosses the Schell Creek Range between Ely in the Egan Range and Osceola in the Snake Range the whole rock series dips to the east. The east- ern half of the range is comj)osed of Upper Carboniferous limestones carr3ing abundant fossils, while the western is composed of metamor- phic limestones underlain by schistose mica-slates. The character of these later rocks, together with the succession, enables one to correlate them with the Cambrian rocks found in the same range just north of a U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 342. 6Ibid., p. 31. 46 GEOLOGY OB' NEVADA SOUTH OF 40TH PARALLEL, [bull.208. here and also in the Highland and Snake ranges. This implies either an enormous fault or a great erosion gap. Opposite Stampede Gap the writer crossed the valley which lies on the west of the range from a district where there ai^e abundant expo- sures of fossiliferons Devonian and Silurian rocks. At the western base of the range he noted in the foothills fossiliferons strata, appar- ently belonging to the same series, from which, however, he collected no fossil remains. Proceeding farther west he found the whole moun- tain made up of altered massive limestones, with intercalated shales and schistose slates, which belong to the Cambrian. A few miles north of Stampede Gap, at Bristol, Mr. Walcott found the Eureka quartzite of the Silurian at the western base of the mountains, and the same formation about 15 miles south of Stampede Gap on the road from Bennetts Spring to Hiko. Both these places occupy the same relative position at the Avestern base of the range. Between these Silurian foothills and the Cambrian rocks of the main range there appears to be a great break, bringing about juxtaposition of strata which in their normal stratigraphic succession are separated by nearly 2 miles of intervening sediments. This is believed to be the same break as that previously noted farther north, and it may be either a fault or an erosion gap. An east-west fault ai3pears to cut the range transversely at a point about 10 miles southeast of Ely in the Egan Range. To the north of this line is an anticlinal fold which exposes probable Silurian or Cambrian rocks. To the south only the eastern limb of the fold is found, the ridge which represents the western limb being cut off. On the south side the rocks carry Devonian fossils. About 10 miles north of the road which crosses the range between Osceola and Ely Mr. F. B. Weeks* observed, in 1900, a strong north- west fault marked by a profound interior valley. Cambrian rocks on the northeast side of the fault are brought against Ordovician strata on the north. The fault cuts across the entire range. Mr. Howell^ noted a probable cross fault near the north end of the Highland Range. The line of this fault is continuous with a probable fault line sketched by the writer on the Egan Range, just to the west. The writer also saw, a few miles north of this, what is perhaps a par- allel east- west fault, marked by a deep transverse valley in the Egan Range and extending across to the gap which separates the Schell Creek Range from the Highland Range. The displacement of these faults was not measured, but is probably very considerable. At Pioche there are a number of intersecting faults, some belonging to a northwest-southeast system and some to a northeast-southwest system. The main fault observed by the writer runs tlirough the south end of the town, in a northwest direction. It is marked bj'- a "Personal communication to the writer. &U. S. Geog Surv. W. One Hundredth Meridian, Vol. Ill, p. 243 SPURK.] EGAN RANGE. 47 deep guleli, and has the Cambrian quartzite on the northeast side and the Cambrian shale and limestone on the south. This fault has at least 1,000 feet of vertical separation and may have much more. Other faults are parallel to this, and there are a number of northeast- southwest cross faults with considerable displacement. The effect of these is to cause a certain degree of checkering of quartzite and lime- stone. The northeast gulch in which Pioche lies seems to mark one of these faults.'* EGAN RANGE. The Egan Range is the next important range west of the Schell Creek and Highland ranges. Its north end lies just north of the fortieth parallel and is included in the maps of the Fortieth Parallel Survey. It extends due southward nearly 150 miles. TOPOGRAPHY. ; Throughout nearly its whole course the Egan Range consists of a single well-defined central ridge, from which the slopes to the valley on both sides are comparatively steep. In the neighborhood of Ely the ridges are slightlj^ broken up, but this is apparently due largely to the presence of igneous rocks. At the extreme south end, also, the main range splits up into several low ridges. The range is cut through at intervals by transverse valleys connect- ing the vallej^s on either side of the range and very little higher than they. Such valleys are found at Egan Canyon and at Ely. Near the southern end of the range there are other deep transverse gaps, which, however, do not cut clear down to the level of the vallej^s. ARCHEAN ROCKS. Mr. S. F. Emmons * has described the rocks in an outlying ridge on the east side of the range, just south of the eastern end of Egan Canyon. Here the lowest formation exposed is a mica-granite, which is overlain by quartzites and quartzitic schists referred to the Cam- brian. The granite is referred to the Archean. SEDIMENTARY ROCKS. CAMBRIAN. As above noted, Mr. Emmons found overlying the granite at the eastern end of Egan Canyon several thousand feet of quartzites and quartzitic schists, together with a 50-foot bed of argillite. These quartzites are overlain hy limestones. The same locality was observed by the writer from a distance, and on account of the stratigraphy was referred with little hesitation to « These observations are in accordance with those previously made hy Mr. Howell (U. S. Geog. Surv. W. One Hundreth Mer., Vol. Ill, pp. 2,57-361), as the writer discovered since writing the above. &U. S. Geol. Expl. Fortieth Par., Vol. II, p. 488. 48 GEOLOGY OF NEVADA SOUTH OF -lOTH PARALLEL, [bull. 208. the Cambrian. The rocks were not visited, but at the base are heavy beds dipping to the west at an angle of about 30" and striking north and south. These massive beds resemble the Cambrian quartzite and limestone, while above them come more easily eroded limestones, which correspond in thickness and position to the Silurian Pogonip formation. Above the Pogonip on the east face of tlie main ridge (which is separated from tlie spur above mentioned by a trough of erosion) is exposed the Eureka quartzite, which is traceable along the range for several miles northward. The identification of this Silurian makes the reference of the easterly rocks of the outlying spur to the Cambrian safe. Mr. F. B. Weeks '^^ reports that in the summit of the range, about 10 to 12 miles south of Egan Canyon, the following Upper Cambrian fossils, determined by Mr. Walcott, were collected: Obolus (Lingulella) discoidensls H. & W. Obolus (Lingulella) manticiilus White. Obolus (Lingulella) punctatus Walcott. Ophileta? Agnostus, 2 sp. Ptychoparia, 2 sp. Along the soutliern jjart of the Egan Range the west face, which confronts the southern part of Sierra Valley, exposes some magnificent sections of strata. These also were not visited any farther north than the vicinity cf Adams's ranch on White River, near which point they were found to be Devonian. Farther north, however, a thick section of rocks, striking northeast and dipping southeast at an average angle of 30", was exposed, and the circumstance that the strike is diagonal to the north-south face of the range brings it about that progressively lower beds are exjiosed going north. About 2 miles north of the vicinity of Butterfleld Spring what was taken to be Eureka quartzite was seen at a distance; below this occurs a great thickness of more easily eroded limestones, which were referred to the Pogoni'p formation; and beneath these again massive limestones, which perhaps represent the Upper Cambrian. Only a comparatively slight thickness of the latter limestones is exposed, when the dip of the section is reversed and becomes northwest, so that the section begins to ascend toward the north. SILURIAN. Mr. Emmons* noted the finding of Silurian fossils in the limestone in the neighborhood of Egan Canyon. The writer, who crossed the range at this point from Cherry Creek westerly, did not succeed in finding any good fossils, but identified the formations on lithologic and stratigraphic grounds as notably belonging to the Pogonip, the "Personal comnmnicatiou to the writer. &U. S. Geol. Expl. Fortieth Par., Vol. II, p. 488. SPUKR.] EGAN RANGE. .49 Eureka, and the Lone Mountain formations of the Silurian as exhib- ited in the Eureka section. In the easterly spur of the mountains just south of Egan Canyon, as above noted, the whole thickness of the Pogonip strata is exposed, occupjang a valley of erosion between this spur and the main ridge. On the easterly face of the main ridge the Eureka quartzite is exposed, and may be traced across Cherry Creek and still farther north. Above the quartzite, in ascending from Cherrj^ Creek westerly, dark-blue cr^^stalline limestones, similar litli- ologicall}^ to the Lone Mountain limestones of Eureka, and carrying indistinct fossils, were observed. The probable exposure of the Eureka quartzite on the western face of the range, near its southern end, has already been noted in con- nection with tlie probable Cambrian exposures. It is probable that along here not only the Eureka quartzite, but the whole Silurian sec- tion, is exposed. Crossing the separate low ridges which constitute the connection between the southern end of the Egan Range and the Pahroc Range, what is almost certainly the Eureka quartzite was found about 25 miles northwest of Pioche. Here was found a white vitreous quartz- ite, rather coarse grained and upward of 100 feet thick, above which lie dark-graj', comparatively thin fetid crystalline limestones, with the fossils too much altered to be recognizable. This is perhaps the Lone Mountain limestone. These Silurian rocks are exposed only along the eroded axis of an east-west anticline, and to the north and south are overlying rocks from which Devonian fossils were col- lected. The general structure of the beds at this point makes it probable that a little farther northeast a greater thickness of Silurian rocks is exposed, in the valley midway between this point and the Highland Range. DEVONIAN. The western face of the Egan Range about 8 or 10 miles north of Cherry Creek is composed of stratified rocks dipping very gently northwest. These stratified rocks are limestones whose appearance suggests the Nevada formation of the Devonian. A short distance north of these, also on the west face of the range, black, shaly, fetid lime- stones carrying Upper Carboniferous fossils were obtained, wuile south of the supijosed Devonian rocks, in the neighborhood of Cherry Creek, there are exposed Silurian f ormatious, as already mentioned. It is more than x^robable, therefore, that the intervening rocks are really Devonian. Mr.- Emmons has made the same suggestion.* In the canyon which cuts through the range at Ely limestones carry- ing Lower Carboniferous fossils were found. In these limestones are siliceous beds which may perhaps represent the Diamond Peak quartzite of the Eureka section, beneath which there is a slight nU. S. C4eol. Expl. Fortieth Par., Vol. II, p. 488. Bull. 208—03 4 50 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. exposure of shaly limestone which may represent the White Pine formation. No fossils, however, were procured from these beds, and their identification as Devonian is only provisional. At the northern end of the curving spur which joins the main range near this point (PL Y, A), where it passes under andesitic flows just south of Summit stage station Cyathojjhyllum sp. was found, and was referred to the Devonian by Dr. George H. Girty. This Devonian area, however, is small, since at a distance of 2 miles farther south similar limestones carrying Carboniferous fossils were found. Devonian rocks make uj) nearly the whole of the series of low ridges which constitute the extreme southern end of the Egan Range, so far as these rocks were examined bj^ the writer in crossing diagonally from northwest to southeast. In crossing the pass which cuts through the western and main ridge of these mountains, about 10 miles due southeast from Adams's ranch, comparatively thin-bedded fetid lime- stones were found folded into a syncline striking diagonally to the trend of the pass, and carrying the following Devonian fossils, as determined by Dr. George H. Girty: Amphipora? sp. Cladopora? sp. Stromatoporoid coral. Chonetes macrostriatus. Spirifer utahensis. The corals obtained here make up the greater bulk of the rock, which appears, therefore, to have been a Paleozoic coral reef. Both the fossils and the nature of the inclosing rocks are identical with the fossils and rocks found in the Golden Gate Range, directly west of here and about 15 miles distant. Following the road from here southeastward to Pioche, Devonian fossils were again obtained about 12 miles south of the first localitj^ as follows: Amphipora? sp. Stromatoporoid corals. Spirifer mala (small variety). Again about 6 miles farther southeast the following Devonian fos- sils were collected: Fucoid. Prodtictella stibaculeata. Rliipidomella sp. Spirifer disjnncttis. Spirifer iitaliensis. Spirifer strigosus ? Ambocoelia umbonata. Camarotoecliia sappho. Modiomorpha obtusa ? Grammysia minor ? Losonema? sp. U. S. GEOLOGICAL SURVEY JLLETIN NO. 208 PL. V A. EAST FACE OF LOW MOUNTAIN RANGE WEST OF EGAN RANGE AT ELY. JB. TERTIARY VOLCANIC CONE, PANCAKE RANGE, EAST SIDE OF HOT CREEK. Exposed by denudation of overlying lavas and tuffs. SPURR.] EGAlSr RANGE. 51 The structure of the surrounding ridges makes it probable that most of them are Devonian. CARBONIFEROUS. In the extreme northern end of the Egan Range Mr. Emmons'* col- lected probable Carboniferous fossils. On the western front, about 12 miles north of Cherry Creek, the following fossils were collected by the writer and identified by Dr. Girty : Orbiculoidea missouriensis ? Marginif era splendens ? Prodiictus 11. sp. Spirorbis sp. Euoniphalus catilloldes. Between Egan Canyon and Ely it is probable that the Carboniferous rocks cover a considerable area. Near Ely, Carboniferous limestones are abundantly exposed. About 2 miles south of Summit Springs, on the road between Ely and Hamilton, massive semicrj^stalline lime- stones are found which carry a probablj^ Upper Carboniferous fossil that was determined by Dr. Girty as Zaplirentis sp. About 6 miles east of here, on the east side of the narrow valley separating the minor ridge, in which the above fossil was obtained, from the main range, were collected the following Upper Carbonifer- ous fossils: Seminula subtilita? Lithostrotion ? sp. Ftistilina cylindrica. Two miles southeast of the last-named locality, near the western entrance of the canyon which cuts through the range at Ely, dark- gray carbonaceous fetid limestones were found which carry the fol- lowing Lower Carboniferous fossils : Zaplirentis sp. Ortliotlietes ingequalis. Rhipidomella miclielini. Productus serdireticulatris var. Prodiictus n. sp. Spirif er ceiitronatiis. Straparollus liixus. Proetus peroecidens. The black shaly limestone which carries the Lower Carboniferous fauna at the last-named locality passes into a belt of red, yellow, and orange weathering shales, with occasional beds of gray, shaly lime- stone. The thickness of these shales is estimated at from 800 to 1,000 feet. Farther east in the canyon beds of cherty and siliceous limestones also occur in this same series. It is probable that the low- est of these shaly beds are Devonian, but to the south of Ely, above aU. S. Geol. Expl. Fortieth Par., Vol. II., p. 487 52 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. the shales, the more massive limestone comes in above again and extends for 5 or 6 miles at least, striking east and west and dipping gently south. On the southeastern slope of Hamels Peak, some miles south of Ely, the fossils named below were collected by Mr. F. B. Weeks,^ and were determined by Dr. Girty. Regarding this collection, Mr. Girty states "The fauna has a similar fades to that of the Marion formation of the Kansas section, which Prosser regards as a true Permian fauna, and it probably can be safely correlated with the Marion." Producttis sp. Nuculana cf . obesa. Pleurophortis ? sp. Schizodus ? sp. Straparollus catilloides. Pletirotomaria htimerosa ? Bulimorpha per acuta. Murchisonia, near marcouiana. Naticopsis ventricosa ? Bellerophon sp. Domatoceras ? sp. Ostracoda. Bakewellia parva. IGNEOUS ROCKS. On the west side of the Egan Range, just north of Egan Canyon, a series of low hills are composed of basalt. One of these hills has a conical shape practically unmodified, and, from the circumstance of this slight erosion, the age of the lava must be very recent. Farther south, also on the west side of the range, is a considerable mass of volcanic rock which has filled up the vallej^ between the southern end of the Long Valle}^ Range and the Egan Range north of Ely. This is, in general, a dacite-andesite and has been deeply eroded, indicating greater age for it than for the basalt. At the southern end of the range, in the sei3arate low ridges which form the connection of this range with the Pahroc Range, there are large areas of quartz-latite which seem to be continuous with similar lavas occurring in the northern end of the Golden Gate Range and on the easterly side of the Grant Range in the same latitude. As in the other cases described, it is plain that these outflows occurred subsequent to the formation of the deep valleys between the limestone ridges, for the volcanic rock either fills up such valleys or has been poured into them without quite filling them up and now forms their floor. Nevertheless, this volcanic rock is also deeply eroded, and therefore its age is not recent. It may be considered as very late Tertiary or early Pleistocene. a Personal commuication to the writer. SPURR.] EGAK RANGE 58 DIKES. At tlie western entrance of the canyon wliich cuts through the range at Ely a dike of hornblende-tonalite-porphjay was noted. Farther east in the eanj^on occur a number of other siliceous dikes. These dikes probably connect with a larger body farther south, which seems to form the crest of the range in the ^dcinit5^ of Howells Peak. Just west of the town of Cherry Creek occur a number of dikes which are apparently connected with a larger igneous body a little farther north. Specimens of these dikes show them to be chiefly quartz-monzonites. STRUCTURE. The extreme northern end of the range is said by Mr. Emmons^ to present an anticlinal fold striking northeasterly, and so diverging from the general trend of the mountains. Farther south, but still north of Egan Canyon, the general structure is plainlj^ synclinal, and has the same northeasterly trend. This syncline must succeed the anticline to the southeast. In the vicinity of Egan Canyon, on the eastern side of the range, the strata on the eastern limb of this syn- cline dip to the Avest at angles of from 30° to 45°, which gradually grow less to the west until, at a point about 8 or 10 miles north of Cherry Creek, and on the west side of the range, easterly dipping strata constituting the other side of the syncline are found. Between the Cambrian rocks on the eastern side of Egan Canyon and the same formations on the west face of the Schell Creek Range, only a few miles to the east, there is probably an anticlinal fold occupying Steptoe Valley. From Egan Canyon south the Egan Range may be seen to consist of stratified rocks as far as Ely, but the general northeasterly trend of the beds at Egan Canyon changes to a northwesterly one in the mountains north of Hercules Gate, about 10 miles north of Ely. The general structure of the mountains at this point seems lobe synclinal, the western limb of the fold being exposed in the Devonian limestone lying just south of Summit stage station on the road between Ely and Hamilton. These limestones dip to the east at an angle of 20°. From Ely south for a number of miles the strata are not conspicu- ously folded, but dip gently in various directions, chiefly to the south. The whole southern end of the range, however, from a point about 10 or 15 miles south of Ely as far as the point where the main range begins to split up into several, shows beds which strike uniformly northeast, at an angle with the general north-south trend of the mountains. The farther south one goes the more easterly becomes the strike of the strata, until, in the series of low ridges at the south- a U. S. Geol. Expl. Fortieth Par., Vol. H, p. 486. 54 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL. [BULt..208. ern end of the range, it swings aronnd to east-west and then to south- east, and so runs into the Pahroc Range, where it becomes due north and south. In this southern i3art of the range many parallel open folds are exposed. On the west face, about 30 miles north of Adams's ranch, in Sierra Valley, the axis of a broad syncline may be traced, with the rocks on both sides dipping from 10° to 30°. This is followed to the south hy a slight anticline and this by a broad syncline, whose axis cuts the mountains about 10 miles southeast of Adams's ranch, at the pass through which runs the road to Pioche. South of here the succeeding anticlines and synclines are frequent and regular. Since their strike is transverse in general to the trend of the ridges and since different ridges are composed of the same i-ocks, the folds may be traced from one to the other for long distances. Thus, south of the synclinal fold above described a broad anticline was observed, which comprises the rocks for a distance of about 10 miles to the south and which has in general an east-west trend. South of this a comparatively^ narrow syncline exists, and south of this again an anticlinal fold, which after swinging from an east-west to a south- easterly direction, appears to change still more. Mil it enters the Pahroc Range with a north-south trend and constitutes the chief fold of these mountains. In general, therefore, the Egan Range consists of open and sym- metrical anticlines and synclines, with the rocks rarely dipping more than 30°. In general these folds trend more easterly than the general trend of the mountains, and thus a number of succeeding folds are exposed. FAULTING. In the southern part of the range several deep transverse valleys suggest fault lines, but the examination was too hasty to be sure of their existence. ORES. At Mineral City, just west of Ely, lead, silver, and gold, with son>e copper, are obtained. At this locality'' a number of siliceous dikes cut up through the limestone, and seem to be connected with the miner- alization. In the neighborhood of Elj^ there are considerable ore deposits. At Cherry Creek also the dikes have perhaps brought about the deposition of the minerals. Some of the ore deposits here run comparatively high in gold and silver. LONG VALLEY RANGE. Long Valley Range consists of low limestone mountains. Its south- ern end, just east of Hamilton, is united with the White Pine Range bj^ a series of connecting north-south parallel ridges. On the north it extends up into the area of the Fortieth Parallel surveys, where it is represented by a series of detached low limestone mountains and finally dies out in the valley. SPURR.] LONG VALLEY EANGE. 55 TOPOGRAPHY. The Long Valley Range consists in general of a single main ridge, on both sides of which the ascent from the base is comparatively gentle. The interrupted form of the northern end of the range, resulting in detached clumps of hills, has probably been brought about b}^ erosion, which has cut deep into the ridge and formed val- lej's which were afterwards filled up with detrital material, on a level with that of the main valleys between the ranges. On the eastern side of the south end of the range a great flood of andesitic lava has filled a former valley to a height equal in general to that of the pre- existing ridges. This andesite itself has been considerably eroded. The valleys which have been cut in it, being younger than the main vallej^ into which the lava was poured, are instructive as to the manner of the formation of desert valleys in general and their filling up with detrital accumulations. Each of these narrow valleys in the lava, often only a few hundred feet wide, presents in a small way all the character- is|-ics of the larger valleys which separate the ranges. In the middle is a flat sage-brush plain, and on the sides long gentle slo]3es of wash proceed from the gullies which cut up the adjoining ridges. In these deposits of the smaller valleys, as in those of the larger valley, there is no trace of deposition in the presence of water, but the vallej^s have filled up evenly and smoothly with dry material, distributed perhaps in part by rivulets and by wind storms. SEDIMENTARY ROCKS. CARBONIFEROUS. At the south end of the range a section was followed along a portion of the road between Hamilton and Ely. The rock hei^e is a limestone, often cherty or aphanitic. Under the microscope the chert shows cross sections of organic forms. The western edge of the section yielded the following Upper Carboniferous fossils, which were deter- mined by Dr. Girty: Marginifera imiricata? Productus prattenianus. Prodtictus inflatus? Farther east the following Upper Carboniferous fossils were col- lected from the same limestone at a horizon several hundred feet higher than the above : Fenestella? sp, Campophyllum torquium? Productus prattenianus. Fusulina cylindrica. Rhombopora lepidodendroides. Fistulipora? sp. Productus semireticulatus. 56 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. Only about 1,000 feet of strata are exposed in this section, owino- to the low dip of the rocks. On the north end of the range the separated groups of low moun- tains above mentioned appear to be almost entirelj' composed of Car- boniferous limestone. They are so shown on the maps of the Fortieth Parallel Survey. Tlie writer collected two lots of Upper Carboniferous fossils at the northern end of the limestone mountain which lies just east of Franklin Lake and the northern end of Ruby Lake. This is ]3ractically the northern terminus of the Long Valley Range, although in the Fortieth Parallel maps it is given under the head of the Ruby Group of Mountains. According to Dr. Girtj^'s determination, the first locality yielded Marginifera splendens ? The second locality afforded the following: Chonetes flemingi. Productus subliori-idus. ProdiTcttis mi-iltistriatus. Spirifer cameratus? Spiriferina pulchra. Semintila mira. South of the lava area which fills the vallej^ between the Long Val- ley Range and the Egan Range, on the road from Hamilton to Ely, there is a narrow spur of mountains running from the neighborliood of Summit stage station to the Egan Range, south of Ely. This may be considered as an outlying spur of the Egan Range, but yet may extend beneath the lava and so form a connection with the Long Valley Range. From the rocks of this spur at a point just south of Summit station a Devonian coral was obtained. Farther south in the same ridge are Carboniferous fossils, as described under the head of the Egan Range (see p. 51). IGNEOUS ROCKS. LAVAS. The great mass of lava .Avhicli flanks the eastern side of th^ Long Valley Range proper at its lower end has alread}^ been mentioned. The extent of this patch of lava to the north is uncertain, but prob- ably is not more than 10 or 15 miles. To the south it passes under the Pleistocene accumulations of Sierra Valley, while to the east and to the west it abuts against the limestones of the Egan and the Long Valley ranges. As noted above, this lava has been considerably eroded. Thin sections of the rock show it to be in general a dacite- andesite, the prevalent type being a dacite containing augite, biotite, and hornblende. STRUCTURE. FOLDING. A section taken at the southern end of the range shows a mono- clinal structure for the main ridge. In reality, however, this is the SPtTRR.] GOLDEN GATE EANGE. 57 east side of an anticline whose axis lies in a narrow valley to the west of the main ridge and wiiose easterly limb is exposed in the next ridge to the west (see fig. 1, p. 66). The spnr of Devonian-Carboniferons rocks described on page 56 is separated from the main ridge by Pleistocene deposits and by lava, and the structural connection is not shown, but in itself it exhibits a series of somewhat closely compressed regular open folds with north- south strike, changing to a northwest-southeast strike as the si3ur approaches the Egan Range. In this minor ridge there is exjjosed, beginning with the most westerly fold, an anticline, a syncline, a sec- ond anticline, and a second s^yncline. For the main ridge of the Long Valley Range the general strike is seen to be parallel to the general trend of the mountains; that is, a little east of north. At the north end of the range, at the fossil local- ities, a slight syncline with a general north-south strike was observed in the Carboniferous limestone. GOLDEN GATE RANGE. The Golden Gate Range scarcely deserves a separate name, on account of its comparative insignificance. This name is applied to a connected series of low mountains which lies to the east of the Grant Range, and properly has a north-south extent of not more than 25 miles, with an average width of 3 or 4 miles. On the south the Golden Gate Range is connected by low hills with the northern exten- sion of the Hiko Range, while on the north the range dies awa}^ into the Sierra Valley. Twentj^-five miles north of the north end of the range there is a chain of low hills running north and south and lying midway between the White Pine Range and the Egan Range. These hills might perhaps be considered as the northern continuation of the Golden Gate Range, the intervening portion being covered up by the Pleistocene accumulations of Sierra Valley. TOPOGRAPHY. The mountains which make up the Golden Gate Range are entirely detached from one another, and are separated by narrow stretches of Pleistocene valley deposits, on a general level with the vallej^s on both sides of the range. The separate groups are sometimes composed of stratified rocks and sometimes of lava. The hills of stratified rock are scarped along the axes of anticlinal folds. They are therefore scarped on both sides Avhen they are synclinal, while when they are anticlinal the}' have in general smooth sides with a sharp downcutting in the center. The groups which are composed of volcanic rocks have naturally a milder and more uniform topography. SEDIMENTARY ROCKS. SILURIAN. An isolated butte at the northern end of the Golden Gate Range, not verj" far from Adams's ranch on White River, exposes a verj^ inter- 58 GEOLOGY OF l^EVADA SOUTH OF 40TH PARALLEL, [bull. 208. esting- section of Silurian rocks. The beds here striliie N. 35° W. and dip 30° NE. At the base of the section is 300 feet of thin-bedded, somewhat fetid limestone and limy shale. Above comes 250 feet of white vitreous quartzite, which is undoubtedly the Eureka formation. Above this comes about 800 feet of comparatively massive brownish limestone (the Lone Mountain formation). At a point about 150 feet below the bottom of the Eureka quartzite, in the Pogonip lime- stone, Ordovician fossils were found. They have been determined by Dr. Girtj^ as follows: Ortliis perveta. Maclurea sp. Murchisonia sp. Pleurotomaria sp. Leperditia bivia. lUaeniTS sp. Trilobites undet. DEVONIAN. Southwest from this butte and about 10 miles distant is a consider- able clump of hills, which forms one of the chief features of the range. A section of about 2,000 feet of limestone is here exposed. The lower 1,000 feet is of limestone, which in places has the peculiarity of weathering brown and craggy, like quartzite. The upper 1,000 feet is composed of shale and thin-bedded limestone. In the lower limestone, where it was examined, the rocks are chiefly composed of corals and constitute, therefore, part of a Devonian coral reef. The same reef, with the same corals, was found in the ridges which form the southern continuation of the Egan Range, 12 or 15 miles east of here. The following Devonian fossils were identified by Dr. Girty: Amphipora? sp. Stromatoporoid coral. Indeterminable gasteropod. PLEISTOCENE. As before noted, the hills of the Golden Gate Range are surrounded and often separated by accumulations of Pleistocene material. This material is generally angular and bears the marks of having been brought to its present position by the influence of rains, wind, and gravity, not by stream or lake action. Probably this Pleistocene forms a veneer over underlying Tertiary deposits, as is the case in the next valley to the west — Railroad Valley. In the neighborhood of the Silurian butte above mentioned is an extensive deposit of calcareous hot spring tufa, covering apparently an area of several square miles and eroded into hills and bluffs in places 40 feet high. Within this area active hot springs are plentiful. IGNEOUS ROCKS. Several of the eminences of the Golden Gate Range are composed of volcanic rocks, which also surround some of the hills of stratified SPURR.] aOLDEN GATE AND HUMBOLDT RANGES. 59 rocks and apparently extend to the east to the southern end of the Egau Range, as represented on the map. A specimen of the lava from the north end of the Golden Gate Range proved to be quartz-latite. STRUCTURE. FOLDING. In the stratified rocks of the Golden Gate Range the strike runs diagonally or transversely to the general trend of the mountains. It has been noted how in the southern part of the Schell Creek and Egan ranges the folds have northeast and southwest axes, which are diag- onal to the general trend of these ranges. In the Pahroc Range the trend of the axes of folding seems to be north and south, parallel with the mountains. Between the Pahroc and the Egan ranges there is an area containing a number of minor cross folds, which have a curving axis and which extend to and connect with the folds of the Golden Gate Range. Several of these minor folds seem to die out just west of the Golden Gate Range. The anticlinal fold which marks the rocks of the northernmost and chief group of hills of the range in which the Devonian corals were found may be a continuation of a possible broader anticlinal axis running between the Worthington Mountains and the northern end of the Hiko Range. The folds of the Golden Gate Range lying south of this anticline, comprising two more anticlines with intervening synclines, do not have any visible relation to the folds to the west or south. However, they raay be traced continuously to the east across the several ridges which mark the southern end of the Egan Range. The southernmost folds curve around southeasterly toward the Pah- roc Range, while the northerly ones, diverging from the others, main- tain a northeasterly direction. FAULTING. In the neighborhood of the Silurian butte above mentioned the abundance of hot springs suggests the presence of faults, but this could not be established. HUMBOLDT RANGE. The Humboldt Range is the most important mountain ridge in the Great Basin between the Wasatch and the Sierra Nevada. Its south- ern end only was visited by the writer, and as this has already been mapped and explored by the geologists of the Fortieth Parallel Sur- vey, it is unnecessary here to go into details. But inasmuch as the writer collected fossils in localities from which none had been reported, it is thought advisable to insert this short description. TOPOGRAPHY. North of Fremont Pass the Humboldt Range is exceedingly rugged and precipitous. South of the pass the mountains become lower. 60 GEOLOGY OF KEYADA SOtJTH OF 40TH PARALLEL, [bull. 208. At Hastings Pass tliey are of only moderate height, and the ascent from the base on both sides to the summit is not precipitous. South of Hastings Pass the mountains are still lower, and pass into straggling groups which connect with the northern extension of the White Pine Range. SEDIMENTARY ROCKS. North of Fremont Pass the Humboldt Range consists mainlj^ of Archean rocks, as has been described by King'' and Hague. ^ These rocks consist of a series of gneisses and schists overlying the basal granite and having a thickness of 8,000 or 10,000 feet. Of this series the lower 5,000 feet is in general a mica-gneiss, while the upper 5,000 feet is a hornblendic and dioritic schist, containing veins of quartzite. At the top are beds of limestone and quartzite. Above this gneiss and schist series comes a series of quartzites about 2,000 feet thick. The quartzites are white or yellow-brown in color and contain sec- ondary garnet, hornblende, actinolite, muscovite, biotite, and iron oxide. On them rest unconformably the Paleozoic strata, with the Devonian generally at the base and the Carboniferous above. King notes the resemblance of the quartzite series (which lies unconformably beneath the Paleozoic beds) to similar rocks in the Wasatch Mountains. It is possible also that the thick white and brown Cambrian quartzites exposed in the Snake Range, especiallj'^ in the vicinity of Jeff Davis or Wheeler Peak, may be equivalents of the Humboldt quartzite. South of Fremont Pass the eastern face of the range is composed of easterly or southeasterly dipping limestones. At a i3oint not more than 4 miles south of the pass the. following Coal Measures fossils were collected by the writer from a butte at the base of the mountains. They were determined by Dr. Girty as follows : Fisttilipora sp. Campophyllum torquiiim? Lophophyllnm proliferain. Rhipidomella pecosi. ProcUictiTS sp. Spirifer camerattis. These same limestones continue all along the east face of the range as far as Hastings Pass. On the summit of the pass is found a con- siderable thickness of sandstones mixed Avith fine conglomerates. These the Fortieth Parallel geologists regarded as Devonian of the Ogden formation, which would correspond to the Diamond Peak quartzite of the Eureka section. A short distance west of the summit the Paleozoic rocks are overlain unconformably by thick deposits belonging to the Humboldt Pliocene of the Fortieth Parallel Survey. At the upper edge of the Pliocene deposits the material consists of aU. S. Geol. Expl. Fortieth Par., Vol. I, p. 62. 6 Idem, Vol. 11, p. 528. SPURR.] HUMBOLDT AND WHITE PINE EANGES. 61 large angular fragments of limestone. From some of the largest of these fragments fossils were obtained which were determined by Professor Ulricli as Ordovieian. Leperditia bivia White. Leperditia sp. (nevadensis?). RhjTichonella? Stropliomena minor Walcott. Strophomeiia? nemea H. & W.? Dalmauella perveta? Walcott. Bathynrtis. If Silurian rocks exist in place at this point one may well snppose that they are exposed by means of a fanlt, for otherwise the thick- ness of strata in the mountains seems hardly sufficient to account for their appearance. IGNEOUS EOCKS. North of Fremont Pass the basal rock appears to be mica-granite, as described by King.<* South of Hastings Pass a considerable area is also represented as granite in the Fortieth Parallel maps. STRUCTURE. FOLDING. The general structure of the Humboldt Range is a broad anticline, as has been mentioned by King^ and by Hague,'^ and as can be seen by an inspection of the maps of the Fortieth Parallel. FAULTING. It appeared to the Avriter that Fremont Pass is the line of an east- west fault, and that this explains the abutting of the Paleozoic rocks on the south against the granite and Archean on the north. More- over, the above-mentioned Paleozoic rocks are sharpl}' turned up along this supposed fault line, so that they dip steeply, and their strike swings round from the normal north-south direction to a northeasterly one, so as to be nearly parallel with the supposed fault. The possible existence of a fault along the west side of Hastings Pass exposing the Silurian rocks has been mentioned above. WHITE PINE RANGE. The White Pine Range, as here described, is the southern continu- ation of the Humboldt Range, and its northern end begins about 10 miles south of Hastings Pass, in that range. From this point it extends unbroken southward for 100 miles, with a general due north- south trend. At its southern end it is continuous with the short Grant Range, which topographically and geologically is a part of it, but which is differently named and will be described separately. aJJ. S. Geol. Expl. Fortieth Par., Vol. I, p.64. ''Ibid., p. 193. <.^ Idem, Vol. II, p.528. 62 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLE'^u. [bull. 208. TOPOGRAPHY. The northern jiart of the White Pine Range, from the southern end of the Humboldt Range to the White Pine mining district, consists of a main ridge, which is narrow and not very high, with a number of minor ridges on each side, separated from the main ridge by narrow valleys in which the underlying rock is only partly obscured bj^ Pleistocene detritus. In the vicinity of the White Pine mining dis- trict the mountains grow higher and the small north-south ridges change into a complicated group of irregular mountains. At the same time the main ridge broadens out to four or five times its former width. In the White Pine mining district three mam north-south ridges may be distinguished — that of Pogonip Mountain on the west, the minor one of Treasure Hill in the middle, and that of Mokeamoke Ridge on the east. Still farther east a succession of regular north- south ridges, similar to those just described for the northern part of the range, form a continuation of the southern end of the Long Valley Range. Within the White Pine mining district the mountains reach a height of 10,000 feet above the sea, while to the north and to the south they are considerably lower. To the south of the district also the moun- tains assume something of the same simple character as they do to the north, being made up of regular north-south ridges, and for the most part consisting of a single main ridge. While in the mining district the mountains and valleys are irregular, the topography of the range to the north and to the south is quite conventional, showing a nniform succession of serrated peaks of nearly uniform height, with their sides furrow^ed at comparatively regular intervals by the drainage. Within the mining district the irregularity is due, as will be pres- ently seen, to the local complexity of the geologic structure. Pogonip Mountain, which, near Hamilton, juts boldly out from the main ridge and is the highest peak in the whole neighborhood, has a bold scarp to the north and to the Avest. Throughout the district there are a number of other precipitous cliffs. But in the rest of the range the mountains show the same steep, but yet not abrupt, faces that are characteristic of the other ranges of the region. It was noticed, how- ever, that south of Hamilton the west face of the mountains was rather steeper than the eastern one. SEDIMENTARY ROCKS. CAMBRIAN. Pogonip Mountain is composed of Paleozoic strata which dip in general toward the east, forming the western limb of the syncline whose eastern limb is exposed on the west side of Treasure Hill Ridge. SPUKR.] WHTTE PINP: RANGE. 68 On the western side of Pogonip Mountain Mr. Walcott ^ has deter- mined from fossils the existence of the Cambrian Hamburg limestone of the Eureka section. About 800 feet of the Cambrian is exposed at this point. SILURIAN. Silurian rocks were described from Pogonip Mountain by Mr. Hague ^ during the Fortieth Parallel Survey. Later on the Silurian beds were also visited and reported upon by Mr. Walcott.'' Mr. Wal- cott found in Pogonip Mountain the following formations, divided according to the Eureka section : Section at Pogonip Mountain. Feet. Lone Moiintahi limestone 1, 450 Eiireka qnartzite 350 Pogonip limestone 5, 200 The writer obtained from Mr. Grandelmeyer, of Hamilton, a fossil said to come from a locality about 6 miles south of that place. It was identified by Dr. Girty as Receptaculites sp. and assigned to the Ordovician. DEVONIAN. While Pogonip Mountain is composed almost entirely of Silurian strata, the ridge next east is made up almost entirely of Devonian. Mr. Hague has described the strata and their contained fossils at this point. The formation, divided according to the Eureka section, com- prises the Nevada limestones and the White Pine shales. Besides this Devonian ridge, the writer has also recognized the White Pine Devonian on the east side of Mokeamoke Ridge, where it is repeatedly brought to the surface beneath the Carboniferous rocks by the erosion of anticlinal folds. He has moreover traced it north of the White Pine mining district for some distance along the west side of Mokeamoke Ridge, where it is largely hidden by Pleistocene detritus. CARBONIFEROUS. The third and most easterly of the three ridges at White Pine, Mokeamoke Ridge, is made up chiefly of Carboniferous rocks which carry abundant fossils. A list of Carboniferous fossils obtained from Mokeamoke Ridge in the mining district is given by Mr. Hague. ^^ The writer has traced the continuation of the Carboniferous belt of Mokeamoke Ridge 15 or 20 miles north of the mining district. At a a Mon. U. S. Geol. Survev Vol. XX, p. 191. &U. S. Geol. Expl. Fortieth Par., Vol. II, p. 542. cQp. cit., p. 191. dOp. cit., p. 547. 64 GEOLOGY OF NEVADA SOUTH OB^ 40TH PARALLEL, [boll. 208. point 6 miles north of Hamilton Upper Carboniferous fossils were collected. The following were determined by Dr. Girty: Producttis semh'eticulatus? Spirifer boonensis. Seminula siibtilita? Euomphalus sp. In the same rocks, close by the above locality, but at a horizon about 200 feet higher up, were found the following: ProdiTctus prattenianiis. ProdiictiTS sp. Spirifer boonensis. Seniintila subtilita. The minor parallel ridges which mark the northern end of the range have all the aspect and structure of the Carboniferous limestones. The writer has also found Upper Carboniferous limestones lying directly north of Pogonip Mountain, being separated from the Silu- rian rocks at this point by a heavy east-west fault which deter- mines the northern end of this mountain. Here the following fossils were collected: Lithostrotion? sp. ProdiTctiis sp. Spirifer boonensis. Spiriferina gonionotus. Seminula mira? Bulimorpha chrysalis? On the eastern side of Moteamoke Ridge the writer has traced the Carboniferous rocks continuously across the intervening ranges to the southern end of the Long Valley Range. At the head of AUepaw (Aj)plegarth?) Canyon, which is on the east side of the range, just east of Hamilton, Glyphioceras sp., an Upper Carboniferous form, was found. Half a mile farther east, down the canyon, were found the follow- ing .Upper Carboniferous fossils: Marginifera muricatas, Productus semireticulatus, Productus prattenianus. Still half a mile farther, at the old pumping station for the town of Hamilton, were found: Orhiculoidea sp., Productus seniireticidatus, Productus prattenianus, Marginifera muricata? Along this section the Carboniferous rocks alternate with narrow belts of the underlying Devonian, which is exposed by the erosion of the anticlinal folds. The Carboniferous section here has always at the base the Diamond Peak quartzite of the Eureka section. This quartzite, or rather sand- stone (for it is not actually a quartzite), outcrops all along the westerli base of Mokeamoke Ridge, so far as this has been followed, and has a thickness of several hundred feet — much smaller than at Eureka. Above the sandstone come heavy, blue limestones containing Coal. sPL'iit;] WHITE PINE RANGE. 65 Measures fossils. In the Carboniferous hillocks at tlie northei'u base of Pogonip Mountain conglomerates were found containing joebbles of red and purple chert, closely resembling similar beds just west of here, on the east side of the Pancake Mountains. RHYOLITE ASH. North of the White Pine mining district and on the western side of Mokeamoke Ridge, the broad area of low hills is partly covered by a deposit of stratified rhyoliticash. NearSixmile House, 6 miles north of Eureka, a dike of rhyolite is found which cuts this deposit and shows that the ash is the earlier of the two. It is very likely that this rhyolite ash is of the same age as that ex]30sed at Twin Springs in the Pancake Range. IGNEOUS ROCKS. The existence of a rhyolite dike in the vicinity of Sixmile House has just been referred to. In this neighborhood and farther north one finds, together with the rhyolite ash already described, numerous small buttes of lava which have been eroded into separate patches, but which once evidently were joined together to form a continuous thin sheet which sjjread over this region. Small patches of coarse-grained hornblende-granite have been men- tioned by Hague « as outcropiDing along the base of Pogonij) Mountain. Whether this granite is intrusive or Archean is not stated. STRUCTURE. FOLDING. The main ridge, Mokeamoke, which extends north from the White Pine mining district, has a general synclinal structure. This sjaicline is variously affected by erosion, so that at times one limb is almost completely worn away, giving the range the aspect of being monocli- nal. For the most part, however, this syncline is well shown for a number of miles north of Hamilton. Still farther north, as far as the southern end of the Humboldt Range, the structure was not carefully observed, but in general it consists of a series of gentle ojjen folds trending parallel to the mountain ridges. On Coal Burners or Bald Mountain the attitude of the strata seems to be very near horizontal. Besides the main Mokeamoke Ridge, whose structure, as sketched about 8 miles north of Hamilton, is shown in the accompanying figure nU. S. Geol. Expl. Fprtietli Par., Vol. II, p. 542, Bull, 208—03-^-5 66 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. (fig. 1), there are several minor parallel ridges. North of the White Pine mining district these minor ridges lie east of the main one, form- ing a continuous section which unites Mokeamoke Ridge with the (O-o flj QO > c -1 E Fig. 1.— Sketch section 5 miles north of Hamilton across White Pine Range to the eastern edge of Long Valley Range. (For explanation of numbers see fig. 2.) southern end of the Long Valley Range. These ridges and the accom- panying valleys (in whose bottoms the rock is very little obscured by Horizontal and vertical scale ZOOOfeet above sea. level Fig. 2.— Sketch section through White Pine Range at Hamilton at the junction of White Pine and Long Valley ranges. 1. Cambrian limestones. 6. White Pine shale (Devonian). 2. Pogonip limestone (Silurian). 7. Diamond Peak quartzite (Coal Measures). 3. Eureka quartzite (Silurian). 8. Coal Measures limestone. 4. Lone Mountain limestone (Silurian). 9. Valley wash (Pleistocene). 5. Nevada limestone (Devonian). detritus) expose a series of gentle anticlinal and synclinal folds of similar character to the syncline of Mokeamoke Ridge. The struc- ture here is shown in fig. 2. FAULTING. In the region of Hamilton, where the mountains widen out notice- ably, the structure of the rocks west of Mokeamoke Ridge consists in general of a pronounced north-south trending anticline, which afi'ects the central ridge comprising Treasure Hill and minor eminences, and, farther west, a general syncline, the western limb of which is Pogonip SPURR.] WHITE PINE KANGE, 67 ridge. Within this region also there are a great number of faults, which appear in general to belong to two systems, one having a north-south and the other an east-west strike. The heaviest fault of the region appeared to the writer to be that at the northern end of Pogonip Mountain, where the Coal Measures limestones are brought by a hidden east-west fault directlj^ against the Silurian strata of the mountain. This fault, therefore, must have a vertical displace- ment of from 7,000 to 10,000 feet. On the northwest corner of Pogo- nip IMountain another fault was observed, having a considerably less displacement and a northwest strike. Mr. Hague '^^ mentions another heavy fault on the western side of the same mountain. Between Pogonip Mountain and the Treasure Hill ridge there is also, accord- ing to Mr. Hague, ^ a disijlacement. In Treasure Hill itself Mr. Hague '^ described, and the writer subsequently observed, an east- west fault which crosses from the southern side of Treasure Hill to Pogonip Mountain. It apj)eared to the writer also that the steeply bent anticlinal fold which is exposed in an east-west cross section of Treasure Hill has been faulted somewhat along its axis and the east- ern part relatively downthrust, the fault being probably a normal one. There are certainly many other faults in the mining district, but all the examinations thus far made have been cursor}^ On the western side of Mokeamoke Ridge and in AUepaw (Applegarth?) Can- yon a number of probable east- west faults were observed. It will be noted that this faulting is, so far as observed, restricted to the neighborhood of the mining district. To the north and to the south there is little reason for believing that the mountains are much affected by faulting. The White Pine district, then, bears exactly the same relation to the rest of the White Pine Range as the Eureka district does to the Diamond Range. Both are areas of local and special dynamic disturbance, resulting in folding, faulting, and ore deposition, and in both the special effects die out in a surprisingly short distance. RELATION OF TOPOGRAPHY TO STRUCTURE. In the northern part of the White Pine Range, north of the mining region, there is a distinct tendency toward anticlinal valleys and synclinal ridges. The mountains, therefore, though determined pri- marily by erosion, yet have the location of their ridges and valleys governed by the position of the folds. South of the White Pine mining region the same general peculiarities hold to the southern end of the range. Within the mining region itself the faults introduce a new feature into the topography. The whole district, as before stated, is traversed «Mon. U. S. Geol. Survey Vol. XX, p. 190. ''Ibid., p. 192. cU. S. Geol. Expl. Fortieth Par., Vol. Ill, p. 412, 68 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. by a north-south and an east- west system of faults, with minor diago- nal ones. Some of these are attended by steep scarps. In the same district wliere these scarps occur the folds seem to have directly determined the topograjihy. The Treasure Hill ridge is anticlinal and the valley between it and Pogonip Mountain syn- clinal. But Mokeamoke Ridge and the ridges to the west are syn- clinal, witli anticlinal valleys, indicating a long-continued erosion period. The folding of the ridges to the west of Mokeamoke Ridge was then distinctly later than that of the ridge itself and later than that of the range in general. The faults of the mining district appear to belong also to the same recent epoch as the associated folds. Those of Treasure Hill have apparently been affected very little by erosion, and are marked by scarps which seem to represent very closely the vertical displace- ment. The same seems to be true of the heavy fault which forms the northern end of Pogonip Mountain, which has already been mentioned. ORES. The structurally complicated region around Hamilton has been the site of rich ore deposition. The ores are distinctly connected with the fault fissures and have formed largely in their vicinit3^ Mr. Hague "- describes the occurrence of the silver deposits of Treasure Hill as (1) in fissures, striking east and west; (2) in deposits between the limestone and shale; (3) in beds or chambers in the limestone and parallel to the stratification of the rock; and (4) in the regular seams or joints across the rock bedding, most frequently with a north- south trend. The minerals found in the mining district comjjrise quartzite, calcite, gypsum, fluorite, barite, black oxide of manganese, rhodochrosite, cerargyrite, galena, cerussite, and azurite. The dis- trict once had a population of many thousand, but at present there is very little activity. QUINN CANYON AND GRANT RANGES. The Grant Range is really the southern extension of the White Pine Range, there being no decided break between the two. It has a length from north to south of about 30 miles. Tlie Quinn Canyon Range is closely connected with the Grant Range, being separated only by a narrow rock-cut valley, whose bottom is for the most part comparatively free from detritus. It is, however, offset from the Grant Range to the west. The Quinn Canyon Range is broad and short, having a north-south extent of about 25 miles, and an east- west extent of nearly 20 miles. TOPOGRAPHY. The Grant Range consists of a single main ridge, rather flat and broad on toj^, and cut up deeply by the smaller mountain valleys, aU. S. Geol. Expl. Fortieth Par., Vol. Ill, p. 418 SPURR.] QlTIlSriSr CANYON AND GRANT RANGES. 69 which run out into the wide detritus-filled main vallej's. These smaller valleys and their auxiliary gulches are generally bounded by steep walls. In general, the main mountain fronts, on the east and west, are also steep. The south end of the range, which lies just east of Garden Valley, decreases graduallj^ in height, and so passes into a series of low buttes which run out into the valley. The Quinn Canyon Range is bounded hy steep cliffs on the east, west, and north sides of its northern half, and the small vallej'^s and ravines which have been worn in this half are guarded by the same precipitous walls as in the Grant Range. This part of the range is cut out of limestone; hence its rugged and irregular topograph 3^ The southern part of the range is a mass of volcanic rocks, which, how- ever, have been extensively eroded. The type of topography is nat- nrally quite different from that in the limestone region, the distribu- tion of the valley's being regular and the rocks being cut up into steep but not precipitous mountains. The southern end of the range also appears to have a more gradual descent into the plain that has the northern. SEDIMENTARY ROCKS. CAMBRIAN. In the foothills at the north end of the Qninn Canyon Rapge and to the north of the abrupt scarj) which limits the northern end of the mountain proper an exposure of rustj-brown shal}'' limestone was found in a canj^on, from which fossils were collected. They were determined by Mr. Walcott as Cambrian. These were the onlj^ Cambrian rocks found in the two ranges. Immediately" to the south, in the high mountains of the Quinn Canyon Range, the rocks are Silurian and probably also Devonian, and indeed an outcrop of undoubtedly Silurian quartzite (Eureka formation) was found only a short distance east of the Cambrian locality. The atti- tude of the beds in both outcroj)S makes it clear that between the two there is a heavy fault, and from the lack of faulting in the Quinn Canyon Range proj)er it is clear that the fault does not run in a north-south direction, but must run in a general east-west direction, not far from the base of the heavj' scarp which delimits the mountain at its north end. SILURIAN. On the steep west face of the northern end of the Quinn Canyon Range the mountains near the base consist of massive, often shaly, dark-blue to gray-blue limestone, much broken ^.nd veined as a con- sequence of granitic intrusions. On account of the alteration the organic remains obtained from this limestone are not identifiable. Six hundred or 800 feet above the base of the limestone, as exposed, comes about 200 feet of hard white vitreous quartzite, which one at once recognizes as probably the Eureka formation. Above this quartzite comes upward of 4,000 feet of gray-blue extremel}" massive limestone, extending to the top of the mountain and weathering into 70 GEOLOGY OF ISTEVADA SOUTH OF 40TH PARALLEL, [bull. 208. smooth, perpendicular, pinnacled cliffs. This same limestone was found all along the north end of the mountain scarp, and also forms the precipitous cliffs on the east side of the mountain front, opposite the Grant Range. In some low foothills on the northern slope of this range, facing Railroad Valley, the following Ordovician fossils (determined bj^ Pro- fessor Ulrich) were found by Mr. F. B. Weeks ^' in 1900: Girvanella sp. undet. Ortliis n. sp. (cf. O. liolstoni Safford). Dalmanella perveta. Ortliis tricenaria ? Cf. Strophomena nemea H. & W. Zygospira n. sp. A large species, i inch or more wide. Three undetermined brachiopods, possibly referrable to Platystrophia. Orthodesma sp. tindet. Lophospira. Cf . Plenrotomaria lonensis Walcott. Orthoceras. Leperditia (near L. fabulites Conrad). Leperditella sp. Primitia (near P. celata Ulrich) . BathynriTS (1). Bathyuriis (2). Bathynrns (3). Within the main range, on the slopes of Big Creek, in the north- western part of the range, the following Ordovician fossils were col- lected hy Mr. Weeks, determined by Professor Ulrich: Receptaculites mammilaris Newberry. Receptaculites ellipticus Walcott. Plates of a large Carabocrinns similar to one occurring in shales of Blacli River age of Minnesota. Plates of Carabocrinns ? with pustulose surface. Monotrypa sp. undet. Batostoma sp. undet. Ortliis n. sp. (near O. liolstoni Safford). Orthis pogonipensis H.& W. (cf. O. perveta). Ortliis tricenaria Conrad (small form). Orthis lonensis ? Walcott. Maclurea sp. undet. (near M. bigsbyi). Gyronema sp. nov. (near G. semicarinatum Salt. sp.). Gen. et sp. nov. (related to Oxydiscus and Conradella). Orthoceras (small species). Endoceras sp. undet. (with " Colpoceras " type of siphuncle). Leperditia n. sp. (semipunctate). Leperditia n. sp. (elongate bivia). Leperditella sp. (near germana Ulrich) . Leperditella sp. with ventral swelling in left valve. Schmidtella n. sp. (near S, crassimarginata). Aparchites sp. undet. Tetradella ? sp. nov. Cranidia and pygidia of six (? 5) species of Trilobites. "Personal communication to the writer. SPURR.] QUINN CAlSrYON AND GRANT RANGES. 7l On the east side also the Eureka quartzife again appears and can be contiuuonsly traced for long distances, thus becoming an impor- tant aid in the studj^ of the stratigraphy. In the valley which sepa- rates the Quinn Canyon Range from the Grant Range the Eureka quartzite outcrops on both sides, on the two limbs of an anticlinal fold froDi which the valley has been eroded. In the bottom of the vallej", beneath the quartzite, is found massive limestone, brecciated, hardened, and altered. In the upper part of that portion of the valley draining north (which is separated by a decided divide from that portion which drains to the south into Grarden Valley) the ascent takes one above the horizon of the Eureka quartzite into that of the overlying limestones. Along the course of this nortliern j^art of the valley no good fossils could be found in any locality, but fragments picked up at various points in the canyon have been identified by Professor Ulrich as Silurian. Batostoma? sp. iindet. Bathyuriis? sp. tindet. Leperditella? sp. nndet. Two species. Ortliis sp. (near O. holstoni Safford). Ortliis sp. (near O. tricenaria). Receptacnlites ellipticns Walcott. At the divide above mentioned tlie stratified rocks are hidden ])y later volcanics. A short distance south of the pass, however, the Eureka quartzite is again encountered, and above it the same heavy limestone as appeared in the Quinn Canyon Range. These rocks extend quite through to the eastern face of the Grant Range. On the lower part of Cherry Creek, after passing the volcanic area, dens© blue limestone is encountered, and farther down the Eureka quartz- ite. From the limestone beds, a few hundred feet below the quartzite, the following Ordovician fossils were obtained and determined by Professor Ulrich. Eccyliopterus sp. tindet. Encrintirns sp. nndet. Isotelns ?. Lingula sp. nndet. The Eureka quartzite, dipping to the east, forms the eastern front of the Grant Range for some miles north of Cherry Creek, and then, on account of the irregular erosion of the mountain front, passes into tlie foothills, where it can be traced for a nuinber of miles farther north. DEVONIAN. No Devonian fossils were obtained from either the Quinn Canj^on or Grant ranges. As already noted, however, the thickness of the lime- stone section which is exposed above the Eureka quartzite is upward of 4,000 feet in both ranges. In the Eureka section <* the thickhess of the Silurian Lone Mountain limestone above the Eureka quartzite is aMon. U. S. Geol. Survey Vol. XX, p. 13. 72 GEOLOGY Oi NEVADA SOUTH OF 40TH PAEALLEL. [bull. 208. given at 1,800 feet. There is an unconformity at Eureka between the Eureka quartzite and the overljdng limestone. Nevertheless, it is very likely that the upper portion of the massive limestone observed in the Quinn Canyon and Grant ranges includes part of the Devonian limestone of the N.evada formation. CARBONIFEROUS. On the eastern slope of the Grant Range, north of Warm Spring, in White River Valley, the following Carboniferous fossils were collected by Mr. F. B. Weeks'^ and determined by Dr. Girty: Chonetes sp. Chonetes illinoisensis. Derbya kaskaskiensis. Prodtictella ? near concentrica. Sph'ifer centronatus. Camarotoechia sp. Eiiinetria verneuiliana. Naticopsis sp. Ostracoda. PLIOCENE. In the northern part of the valley separating the two ranges there are found, uj) to a height of 6,200 feet above the sea, horizontally bed- ded arkoses and conglomerates, made iTp of the fragments of the limestone cliffs above and nevertheless hardened into' solid rocks. This may be a shore formation, and may belong to the Pliocene lake whose sediments are shown in the Pancake Range at Twin Springs and at Hot Creek. The Pleistocene subaerial accumulations hide the Tertiary strata throughout the greater part of the valleys. A hint of the former existence of a Pliocene lake on the west side of Quinn Canyon Range, however, was found in the x>eculiar development of the gulches which furrowed the volcanic rocks. These gulches are deepest at the top, and grow progressively shallower lower down, until near the bottom they die out entirely. This may signify that the development of the gulches began above the surface of the Plio- cene lake and as the lake became lower the gulches were forced to extend themselves, but naturally accomplished only a small amount of cutting in those new portions as compared with the long-established upper parts. IGNEOUS ROCKS. RHYOLITE AND GRANITE. On the west side of Quinn Canyon Range, directlj^ east of Twin Springs, are found great masses of siliceous igneous rocks which widen in extent farther south and cover up the whole of the range. ^ At the northern end of the mountain valley which separates the most easterly part of the range from the westerl}^ part, along which the Quinn Canyon n Personal communication to the writer. I>Q. K. Gilbert, U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 122. SPURB.] QUINN CANYON AND GRANT RANGES. 73 road runs, the volcanic rock has been stripped down to the underlying limestone, which is found to be traversed by great dikes of acid rock, varying from coarse to fine in texture. The overlj-ing rhj^olite and the dike rocks were examined microscopically. Of two specimens of the dikes one was a coarse biotite- hornblende-granite and the other a very fine biotite-granite-porphjay, the same mineralogically as the coarse variety, but both mineralogically and structurally far more closelj' connected with the rhj'olite.'* It is probable, therefore, that the dikes and the massive eruptions constitute different jparts of the same igneous mass. BASALTIC VOLCANICS. In the small valley between the two ranges, thin-bedded basaltic volcanics occur just south of the pass and stretch over a considerable area. These rocks are fine grained or glassy and show very beautiful flow structure, in strong contrast to the massive, rugged rhj^olite in the hills above them. Specimens examined microscopically show the rock to be a basalt carrying augite and hornblende. The basaltic rocks extend for some distance along Cherry Valley. QUARTZ-LATITES. On the east side of the Grant Range, near the point where it joins the White Pine Range, the outljnng foothills which bound the south- ern or southwestern end of Sierra Valley are evidently comjDosed of dark-colored volcanic rock. This is not far from similar volcanic areas which form the northerly continuation of the Golden Gate Range, and is very likely of the same nature. From one of the volcanic hills of the Golden Gate Range near this point a specimen i^roved to be quartz-latite, containing augite, biotite, and hornblende. RELATIVE AGE OF LAVAS. In these two ranges the rhyolites are distinctly oldest, as shown not only by the fact that the more basic lavas overlie them, but also by the greater erosion of the rhj^olites as compared with the others. The latite ax3pears to be of intermediate age. It is probable that the rhyolites and the basalts are to be correlated with the corresponding lavas of the Pancake Range, as exhibited at Twin Springs. STRUCTURE. FOLDING. At the west base of the Quinn Canyon Range the distribution of the Eureka quartzite shows that there exists here an anticline with a north-south or northeasterly-southwesterly axis. The north end of the range exposes a broad, very shallow syncline, which succeeds the anticline to the east. In the center of this syncline the beds are horizontal for a considerable distance, and the maximum dip on «.J. E. Spurr, Variations of texture in certain Tertiai-y igneous rocks of the 0'*ea^ j3asin: Jour. Geol., Vol. IX, 1901, p. 601. 74 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. ul iC to t-^ s .a ■ ■2 a "S l=! 03 ° a cS CS ^ ;5 .g ^ fl 0) 0; o a^ o3 "^ 'fl 0) ^ =e O g .& 'S rH •— ' O r-^ O fi ^'S o CM CD S Cs) 13 "cS cS -IJ OJ ^ •r '-I N S cS P "cS e U 03 S "^ a 1 2 1 cS O p! 1 O J w CO ,_J IN c6 6 the two sides is about 35°. The syn- cline is succeeded farther east by an anticline, along which the valley separating the two mountain ranges has been eroded. The Eureka quartz- ite, which appears on both sides of this anticline, allows its being traced easily for long distances. The fold has a general north - northwesterly trend and is visible in the moun- tains of the Grant Range about 8 or 10 miles to the northeast of the north end of the Quinn Canyon Range. At this point it is much sharper than farther south. The eastern limb of the anticline, which is steeper than the western limb, is at the same time the western limb of a syncline which is dis- plajT^ed in the Grant Range. There are some slight minor folds, but the general cross section apjDcars to show a perfect sjnicline at a point just east of the north end of the Quinn Canyon Range. Farther south, in the vicinity of Cherrj^ Creek, the jutting out of the mountains a little farther east, as a consequence of the irregular ero- sion, permits the study of a third anticline, Avhich succeeds the syn- cline, and is a heavy and persistent fold. Looking north from the vicinity of Cherr}" Creek, one sees this anti- clinal fold passing from the side of the mountains into the foothills, so that the strata which at first dip easterly on the mountain face change to a westerly dip, which denotes the eastern limb of the Grant Range syn- cline. These folds have a more north- easterly strike than those farther west, so that the easternmost anticline just described probablj^ strikes across the valley to the low hills which divide the Golden Gate Range from the Grant Range about 20 miles north of Cherry SPURR.] QUINN CANYON AND GKANT RANGES. 75 Creek, and is again exhibited in the strata of these liills. At this point the anticline is joined on the east by a connected series of open synclines and anticlines, which form the low mountains of the Golden Gate Range and extend across to the northern end of the Hiko Range. Fig. 4. -Sketcli section of east front of Grant Eange. Taken 5 miles north of fig. 3 and showing altered position of anticlinal fold with reference to the mountain front. The strikes of these folds become more and more easterly until in the Hiko Range they swing round and become southwesterly, and then, farther south, pass into the usual north-south trend again, having described semicircles. (See figs. 3 and 4.) FAULTING. As alreadj^ mentioned, there is apparently a heavy fault at the northern end of the Quinn Canyon Range, which has brought up the Cambrian rocks on the north side against the Silurian on the south. This was the only fault determined in the two ranges. (See fig. 5.) Quinn Canyon Mountains Rai Iroad Valley Horizontal and vertical scale Fig. 5.— Generalized sketch section of north end of Quinn Canyon Mountains. 1. Silurian limestones and quartzites (probably 2. Cambrian limestones and shales. Devonian on top). 3. Chiefly Pleistocene valley wash. Some slight crumpling of the strata was observed on the eastern side of the Grant Range, near Cherry Creek, but this was probablj^ due to the intrusion of the near-by volcanic rocks. In general, the folds of the stratified rocks are even and unbroken. RELATION OF STRUCTURE TO TOPOGRAPHY. As described, the Quinn Canj^on Range is essentially a simple syn- cline, as is also the Grant Range. On the west side of the Quinn Canyon Range, the east side of the Grant Range, and also between 76 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. the two ranges, are anticlines wliicli are marked by deep depressions. In general, therefore, the form of the mountains is one that implies a long period of erosion subsequent to the folding. Although the faces of both these ranges, on the east and on the west, are somewhat abrupt, the apparent continuation of the beds XDast these steep faces without break indicates that the faces are not caused by faulting, but are due to erosion. The north end of the Quinn Canyon Range is probably along a fault, but in this case the Cambrian rocks, which have been relatively upthrust by the faulting, are found in low foot- hills running into the valley, while the downthrust Silurian rocks form abrupt cliffs facing the Cambrian. It seems, therefore, that if the cliff was primarily determined by faulting it is not directlj^ due to upthrnst, but to powerful erosion. WORTHINGTON MOUNTAINS. The Worthington Mountains are a very small group lying north- west of the Pahranagat Range, with which they are connected by a series of hills. They also are connected with and probably form the northern extension ef the Timpahute Range, and on the north the rocks are probably continuous with those of the Grant Range, from which they are separated by a few miles of desert valley. On the west side of the Worthington Mountains there is a series of low hills which form a certain connection between them and the Quinn Canyon Range. Like most of the high mountains of the region, as, for example, the Quinn Canyon Range and the Grant Range farther north, the Worth- ington Mountains have steep sides, averaging perhaps 30° in incli- nation to the horizontal, to the east, west, and north. SEDIMENTARY ROCKS. The northern end of the range was viewed by the writer from a point several miles farther north. From here the rocks are apparently massive limestones, resembling the Devonian and Silurian strata of the Grant Range just to the north, and having a similar strike. These same strata can be traced southward along the flanks of the moun- tains. At the northern end, according to Mr. Gilbert,^ they consist principally of limestone, with some sandstone- The limestone carried abundant fossils, which probably belong to the Silurian. IGNEOUS ROCKS. According to Mr. Gilbert, the northern end of the mountain is flanked on the east by beds of rhyolite, associated with which are the Freiberg silver mines. nU. S. Geog. Sui-v. W. One Hundredth Mer., Vol. Ill, p. 37. spuRR.] WOKTHINGTON AND PANCAKE RANGES. 77 STRUCTURE. At tilie northern end of the range the strata dip westerly about 30°, parallel with the general slope of the range. Farther south the dij) grows continually less, until at the southern end it is horizontal. It was at this point observed by Mr. Gilbert, who interpreted the hori- zontal structure of this bold mountain as determined bj^ faults on both sides, the mountain being an upthrust block between the two. Considering the change in attitude between the south and north ends, however, it may also be that the mountain represents part of a fold whose strike diverges slightl}^ from the trend of the ridge. PANCAKE RANGE. TOPOGRAPHY. The northern end of the Pancake Range lies just east of Eureka, where it terminates in White Pine Valley. North of this termination and across the valley is Coal Burner or Bald Mountain, a prominent eminence which appears to be in geologic continuity with the Pancake Range, but which is more closely connected topographically with the . southern end of the Humboldt Range. To the south the Pancake Range extends in a straggling fashion as far as Twin Springs, a distance of about 100 miles, with a general trend a little west of south. At Twin Springs a narrow pass separates the Pancake Range from the Reveille Range, farther south. There is, however, no real break in the topo- graphic continuity here, and the distinction is therefore somewhat arbitrary. The Pancake Range is low and without striking relief, as its name indicates. The northern end of the range consists in part of lime- stone ridges with general northwest trends, diagonal to the trend of the range. Flanking these limestone ridges are somewhat dissected but nevertheless level-topped volcanic mesas. South of the road between Eureka and Hamilton is a considerable area of shaly Devo- nian rocks, which are eroded into low smooth hills. About 8 or 10 miles farther south, with the covering up of the stratified rocks by later eruptives, a corresponding change in the topographj^ takes place. The single main ridge divides into a number of irregular parallel ridges and the low smooth hills change to higher ones which, though sometimes rounded, are often sharp or conical. The tops of these hills often join to form a general mesa. This type of topog- raphy extends to the extreme southern end of the range. SEDIMENTARY ROCKS. CARBONIFEROUS. In the northern end of the range limestones and conglomerates asso- ciated with thin seams of impure coal have been reported.'* These aMon. U. S. Geol. Survey Vol. XX, p. 96. 78 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bill 208. limestones contain numerous species of Carboniferous fossils. The writer also collected Upper Carboniferous fossils from tlie vicinity of the road which crosses the Pancake Mountains between Eureka and Hamilton. One locality afforded the following species, which were determined by Dr. Girtj^ : Fusulina cylindrica. Fisttilipora ? sp. Derbya sp. Chonetes verneuilianus. Rhipidomella pecosi. Prodtictiis sp. ProtliTctiis nebraskensis ? Margin! f era muricata ? Seniinula subtilita ? Another localit}^ about 2 miles southeast of the first, yielded Chceietes milleporaceus, Spirifer rockymontanus, Phillijjsia s;2>- These fossils were in shaly gray limestone, which was overlain by more massive limestone, interstratified with occasional belts of con- glomerate containing pebbles of quartzite and chert. DEVONIAN. South of the road meiitioned come in the sandy and limy shales of the Devonian White Pine formation. « This shale is associated with beds of brown sandstone which contains plant remains. TERTIARY. On the west side of Hastings Pass, in the Humboldt Range, near the northern end of White Pine. Valley, are sediments to which was given the name of the Humboldt Pliocene, and which were described and mapped by the Fortieth Parallel Survey. These beds were examined by the writer and were found to consist largely of limestone fragments derived from adjacent Silurian rocks. They abut against the mass of the Humboldt Range in such a manner as to show that this range formed their shore line and that they were deposits formed when the valley had practically its present shape. In other parts of the valley the Pliocene deposits are generally covered with Pleistocene accumulations, and are therefore not dis- cernible. Along the Pancake Range, however, on the east side of the extreme southern end of Little Smoky Valley, stratified deposits similar to those on the flanks of the Humboldt Range were found, forming a fringe around the mountains. At Twin Springs the canyon which has been worn transversely across the mountains exposes a section of Tertiary stratified rocks, lying between the Tertiary volcanics. The section shows rhyolite at the base. Above this comes several hundred feet of horizontally bedded n Mon. U. S. Geol. Survey Vol. XX, Atlas sheet 4. SPURR] PANCAKE RANGE, 79 water-laid semiconipacted sandstones, apjiarently derived from the rlij^olite. At the top of this stratified series the white sands change to stratified tufl's and gravels, brown in color and evidently derived from basic lava snch as immediately overlies them. This lava is a solid dark-colored basalt, which forms the uppermost member of the series. PLEISTOCENE LAKE .DEPOSITION. At several points the marks of a comparatively recent body of water, occupying a large part of Big Smoky and White Pine valleys, were observed. On the east side of the Diamond Range, about 10 miles north of Pinto Creek, distinct terraces were observed in the detritus at the base of the mountains. These terraces are several in number and are 50 or 60 feet above the valley floor. Also about 15 miles south of Fish Creek a regular bench com loosed of lava debris was noted on both sides of the vallej^ about 15 feet above the smooth mud deposits of the valley bottom. Farther north, at a point on the Pancake Range just south of the road between Eureka and Hamilton, at the mouth of a gap in the hills, a definite beach bar was noticed, such as forms along gently sloping shores at the mouths of inlets. There was therefore probably a Pleistocene body of water which spread over the greater part of Little Smoky and White Pine valleys. The shore marks above mentioned indicate that this lake was shallow. Tlie final remains of the Pleistocene lake may be considered as still existing in the numerous marshy ponds which are scattered through the White Pine Valley north of the Pancake Range. GULCH DUMPS OR ALLUVIAL FANS. Along the line of junction of the mountains Avitli the valleys, and occasionally forming the low foothills, are sometimes observed accu- mulations of detritus which rise above the level valley floor, and which have such relation to the gulches of the mountains above that it is plain their materials have been derived from their erosion; and in some cases it seems that the amount of material in these dumps is a verj^ large portion of that which has been removed in the excava- tion of the gulches. Where this material is exposed at the surface, it is found to be angular and bearing other marks of having been brought down by torrents. These accumulations are certainly, in part at least. Pleistocene, and are being added to at i^resent. However, they antedate largely the Pleistocene water body above described. They are therefore Pliocene- Pleistocene, and are largely contemporaneous with the water-laid deposits which occur at lower altitudes. IGNEOUS ROCKS. At the northern end of the Pancake Range a body of rhyolite forms the western half of the mountains and extends as far south as the 80 GEOLOGY OF NEVADA SOUTH OF 40X11 PARALLEL. [buli^.S-K. road between Eureka and Hamilton. A short distance south of this road andesite comes in in considerable patches/' This andesite was observed by the writer at intervals for a distance of 10 or 15 miles south of here. It is here generally mixed up with small areas of rhyo- lite. Still farther south rhyolite seems to form the greater part of the range (PL V, B). In the neighborhood of Twin Springs, as men- tioned above, the rhyolite occurs at the base of the section and basalt at the top. STRUCTURE. FOLDING. The area of White Pine Devonian rocks, above described, forms a shallow syncline which apparently gives place to a gentle anticline farther north, and there exposes the Carboniferous limestones. It is possible, however, that it is a fault which brings up these limestones. The syncline has a general northwest strike and is i)lainly continuous with the faulted syncline of the Eureka district, just across the valley, which has Newark Mountain on its eastern limb and the Alhambra Hills on its western. This syncline may be traced across the Pancake Mountains and across the intervening low hills to the White Pine Range, its strike being at an angle to the general trend of the major ridges, although the minor ridges conform to it. FAULTING. The Upper Carboniferous limestones on the road across the range, between Eureka and Hamilton, have perhaps been brought to their Horizontal Scale I 2 smiles Fig. 6. — Generalized sketch cross section of Pancake Range at north side of pass at Twin Springs. 1. Rhyolite, 200 feet. i. Olivine-basalt, 200 feet. 2. Rhyolite sandstone, 600 feet. 5. Valley wash (Pleistocene). 3. Basaltic tnffs and gravels, 100 feet. 6. Faults. present jDosition by an east-west fault, transverse to the trend of the range, for their relation to the Devonian rocks just south of here can not be readily explained by the folding. The accompanying section (fig. 6) shows the structure of the Pan- cake Mountains at Twin Springs. There has been practically no folding here, except where the beds have been locally crumpled bj^ overriding sheets of lava. A series of faults was observed, some of which have a throw of several huudi-ed feet. The fault lines are accompanied by gullies, but not by fault scarps. « gee Mon, U, S, Geol, Survey Vol. XX, Atlas sheet 4. 1 spuRR.] PANCAKE AND DIAMOND KANGES- 81 COAL. lu the northern end of the Pancake Range the Carboniferous rocks carry tliin seams of impure coal, which have been in vain explored for marketable material. "■ DIAMOND RANGE. The Diamond Range may be somewhat arbitrarily defined as begin- ning at Railroad Canyon on the north, and extending southward through the Eureka Mountains to Fish Creek. South of Fish Creek comj^aratively low mountains occur. No decided break separates these from the Eureka Mountains, but they are more closely associ- ated with the Hot Creek Range, and will be described in the latter connection. TOPOGRAPHY. The main part of the Diamond Range, from its northern end to the vicinity of Eureka, consists of a single narrow, somewhat regular ridge, whose divide is in the center. This is sharply cut uj) on both sides, so as to present a succession of well-defined peaks, with deep drainage channels. In the neighborhood of Eureka this simple topographic structure changes to a more complicated one, which is the expression of a geologic structure more comj^licated than that to the north. The mountains in the vicinity of Eureka are considerabl}^ folded, and are traversed by numerous faults, which run in several directions. The result of the erosion of this structurally complicated region is that there have arisen many separate mountain ridges, and the total width of the range has increased. South of the Eureka Mountains the range is composed of a single narrow ridge of stratified rocks, which seem to resume the compara- tively" simple structure of the northern portion. Just south of here the sedimentaries are buried iinder thick sheets of lava. SEDIMENTARY ROCKS. At the nothern end of the Diamond Range, at Railroad Canyon, the rocks have been described by Mr. Hague ^ as light cream-colored limestones dipping to the north under sheets of basalt. These lime- stones are mapped by the Fortieth Parallel geologists ^ as the Lower Coal Measures. The writer traveled along the easterly face of the Diamond Range, from a i)oint just west of Hastings Pass, in the Humboldt Range, to the southern termination. At the northern end of the traverse a sec- aMon. U. S. Geol. Survey Vol. XX, p. 95. b U. S. Geol. Espl. Fortieth Par., Vol. II, p. 5i9. fldem, Atlas, map 4, west half. Bull. 20S— 03 G 82 GEOLOGY OF NEVADA SOUTH OF -lOTH PARALLEL, [bull.308. tion of strata is visible, wliicli, in default of oj)i30i-tiinity for examina- tion, Avas provision allj^ supposed to have the Devonian White Pine shale of Eureka at the base, with the Carboniferous Diamond Peak quartzite above. The thickness of the exposures of these two formations was roughly estimated at from 2,000 to 2,500 feet. Above this section were obsei'ved comparatively massive limestones which were taken to be the Lower Coal Measures limestones, and of these an estimated thick- ness of 4,000 feet was observed. Above these again are heavy brown-weathering massive rocks forming the precipitous crest of the range for a long distance. These were thought to belong to the Webtr formation. About 1,500 feet of this was visible, the top not being seen. Mr. Hague ^* notes that at Chokup Pass, which is within the above section, limestones occur in which no fossils were found. "In the limestone occurs a belt of coarse, although compact, brownish- yellow sandstone, not unlike the sandstone body at White Pine, which lies at the base of the Coal Measures limestone. It measures nearly 300 feet in thickness." This is, perhai^s, the Diamond Peak quartz- ite, as it was afterwards called bj^ the geologists who studied the Eureka district. South of Chokup Pass the same formations occur. In the eastern foothills the Diamond Peak quartzite outcrops, brown, iron stained, friable, and calcareous, resembling exactly the same formation as exposed in the Egan Range, in the canyon west of Ely. The quartzite becomes at times a conglomerate, containing i^ebbles of chert and limestone. It is possible that this conglomerate indicates an erosion interval between the Carboniferous and the underlying Devonian. A few miles farther south, the strike of the Diamond Peak quartz- ite having carried it temporarily under the valley detritus, the eastern foothills are composed of the overlying dark-blue limestone with chert nodules. This limestone cai-ries the following abundant fauna, determined as Upper Carboniferous by Dr. Girty; Fistulipora ? sp. Rhombopora lepidodeiidroides. ArchaBOcidaris sp. Productns prattenianus. Prodiicttis semireticulattis. Productus nebraskensis. Prodnctus nevadensis ?. Sph'ifer boonensis. Seminula stibtilita. Fish scale. Still farther south a change in the structure brings in the Diamond Peak^iuartzite again, together with the underlying Devonian rocks, and the strata rise rapidly to the top of the range. In Chihuahua Canyon, which lies to the east of Diamond Peak, n U. S. Geol. Expl. Fortieth Par., Atlas, map 4, west half. spuRR] DIAMOND KANGE. 83 slightly fetid limestone was found, and at a point about 1,000 feet above the bottom of the series exjDosed were Devonian fossils, as determined by Dr. Girty. Ampliipora ? sp. Spirifer engelmanni. Spirifer, indeterminable. Spirifer uiaia (small variety) ?. Atrypa missouriensis. This is part of the Nevada limestone, for the Devonian White Pine shales come in about 500 feet above. South of here the geology has been thoroughly worked out during the surve}^ of the Eureka mining district, which survey embraces the region from Diamond Peak on the north to White Cloud Peak on the south. Within this area is found exposed the best Paleozoic section yet studied west of the Rocky Mountains, comprising strata from the Prospect Mountain Cambrian quartzite, through the Cambrian, Silu- rian, Devonian, and Carboniferous.^ South of the Eureka mining district proper, the single ridge into which the mountains contract is shown in the geologic maj) of the Eureka district^ to be composed of the Silurian Pogonip limestone. This limestone extends farther south till covered up by volcanic flows. IGNEOUS ROCKS. At the northern termination of the Diamond Range the stratified rocks are overlain by flows of basalt. '^ Between this point and the region around Eureka no igneous rocks were observed. The Eureka district, however, lias been the seat of volcanic activity. Among the volcanic rocks, hornblende-andesite, dacite, rhyolite, pyroxene-ande^ site, and basalt have been described bj'^ Mr. Iddings.*^ Granite-i^or- phyry is also found as a dike rock. The volcanic rock which occurs at the southern termination of the range has been determined by the writer, a few miles farther south, to be rhyolite. STRUCTURE. North of the Eureka district the stratified rocks of the Diamond Range are bent into a series of gentle folds which in general strike nearl}^ with the trend of the range. In the region between Chokup Pass and Railroad Pass these folds seem to consist of an anticline on the east side, with its eastern limb almost buried by the detritus of the valley, followed by a shallow broad syncline to the west, and this « Arnold Hague, Geology of the Eureka district, Nevada: Mon. U. S. Geol. Survey Vol. XX; C. D. Walcott, Paleontology of the Eureka district: Mon. U. S. Geol. Survey Vol. VIII. &Mon. U. S. Geol. Survey Vol. XX, Atlas sheet 4. c Arnold Hague, U. S. Geol. Expl. Fortieth Par., Vol. II, p. 549. dMon. U. S. Geol. Survey Vol. XX, p. 233 et seq. 84 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 308. in turn by an important anticline wliicli seems to form tlie western edge of the mountains. At Chokup Pass Mr. Hague" notes tlie general anticlinal structure of the mountains, the summit of the anticline occupj-ing the crest of the pass. This is the same anticline as has just been noted as form- ing the western face of the mountains to the north of the pass, the slight divergence of the strike of the fold from the trend of the moun- tain bringing the fold to this place. Farther south the continued divergence brings the axis of this anticline at one point down to the easternmost foothills. As a consequence of this, the syncline and anticline which lie to the east are covered by valley detritus. Farther south still, as one approaches the vicinity of Diamond Peak, the trend of the folds changes slightly and again brings the crest of the eastern- most anticline to the summit of the range. South of Diamond Peak the country in the neighborhood of Eureka is a region of special dynamic disturbance, and is folded and faulted to a remarkable degree. Except in this district, however, no faults have been observed in the range. RELATION OF STRUCTURE TO TOPOGRAPHY. North of the Eureka district the structure has been so far influ- ential that the trend of the range corresponds nearly to the general strike. In the Eureka district the complicated topography is dependent upon the increased complications in the geology, but the forms appo^ir to be directly due to differential erosion. Most of the faults here are oblique to the general trend of the range. Along these faults valleys or canyons are sometimes found, and sometimes moderate scarps; but that these latter are due to differential erosion is shown by the fact that it is sometimes the downthrown side of the fault that appears as a scarp and sometimes the upthrowu, depending upon the nature of the beds. ORES. The whole district around Eureka has been the site of abundant ore deposition, a phenomenon plainly connected with the dynamic disturbances which have brought about the complicated folding and faulting (and indirectly the topography) and with the volcanic out- bursts. The ore deposits of Eureka have already been thoroughly studied.* Outside of this region the range is not remarkably ore bearing. HOT CREEK RANGE. The Hot Creek Range is separated at its south end by a narrow pass from the Kawich Range, which otherwise is continuous with it. aU. S. Geol. Expl. Fortieth Par., Vol. II, p. 549 &J. D. Curtis, Silver-lead deposits of Eureka: Mon. U. S. Geol Survey Vol. VII; Arnold Hague, Geology of the Eureka district: Mon US Geol Survey Vol. XX. SPURR.] HOT CREEK EANGE. 85 From here it runs north 70 miles and disappears in a valley a few miles sonth of the latitude of Eureka. In the same line, farther north, occurs the Piiion Range. The northern continuation of the Hot Creek Valley divides the mountains into an east and a west half. The western half is the continuation of the Hot Creek Range proper, while the eastern one runs north and joins the Eureka Mountains. SEDIMENTARY ROCKS. SILURIAN. At the eastern end of the canyon, at Hot Creek, the following sec- tion was observed, beginning with the bottom: Section at Hot Creek. Feet. 1. Tliin-bedded. dark-blue frosty-lustered limestone, calcite- veined, with impei'f ect fossil remains 400 2. Massive white quartzite .- 400 3. Thin-bedded daik-blne limestone 200 4. Shales mixed with thin-bedded limestone 1 , 000 5. Massive light-gray coarsely crystalline limestone, constituting the top of the mountain .- .-. 500 . Three miles west of this localit}^, at the ranch near Hot Springs, there comes in, below bed No. 1, more massive siliceous light-gray, coarsely crystalline or aphanitic limestone about 600 feet in thick- ness. This makes about 1,000 feet of limestone in all below the quartzite. From the first-named locality, at a point about 200 feet below the quartzite, Ordovician fossils were obtained. The following were deter- mined by Professor Ulrich : Amphion (sp. near A. salteri Billings) . nisenus (sp. near I. americanus, consimilis. and crassicauda) . Bathynrns sp. iindet. Leper ditia bivia White. Leperditia n. sp. Aparchites sp. tindet. Primitia (sp. near P. celataUlr.). Primitia (? Enrychilina) n. sp. Enrychilina (near E. snbaeqiiata) Ulr. Schmidtella n. sp. ThlipsnraV n. sp. Modiolopsis occidens, Walcott. Macltirea. Tetranota (n. sp. near T. obsoleta Ulr.). Lophospira (cfr. medialis Ulr.). Plenrotomaria ? lonensis Walcott. Triptoceras sp. undet. Orthis n. sp. (near O. holstoni Safford). Dalmanella pogonipensis. H. and W. Batostoma, sp. undet. 86 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. It is, then, plain that the quartzite is the Eureka quartzite of the Eureka section, while the limestone below corresponds to the Pogonip formation and that above to the Lone Mountain. We have here a section of about 3,100 feet of Silurian rocks, comprising 1,000 feet of the Pogonip, 400 feet of the Eureka, and 1,700 feet of the Lone Mountain. A few miles south of the above locality, in the next canj^on to the south of Hot Creek, there were collected from the limestones above the quartzite the following Upper Silurian fossils (Niagara ?), as deter- mined by Professor LTlrich: Halysites catenulatus, large variety. Halysites catenulatus, small variety. Favosites (ramose species). Syringopora sp. iindet. Amplexus sp. nndet. Cyathophyllum sp. undet. Zaphrentis ? sp. undet. Rhynchonella sp. xindet. At Tybo, about 15 miles south of Hot Creek, and also on the east side of the range, the rocks appear to be mainly massive dark-blue limestones with a general westerly dip. This locality was not visited, but a single fossil obtained from these limestones was regarded by Dr. Girty as jjrobably Ordovician, Maclurea aymulata ? From Tybo to the south end of the range, just west of Twin Springs, in the Pancake Range, the east half of the mountains is entirely com- posed of similar limestones. At the extreme south end the limestones are overlapped by the rhyolites of the Kawich Range, which have altered the sedimentary rocks. No fossils were found at this point, but a specimen of the limestone was seen under the microscope to be made up of tinj^ indeterminable organic remains. TERTIARY. On the eastern side of the range, extending from Hot Creek a num- ber of miles in both directions, are gray hills composed of partly consolidated coarse gravel and grit. This material often overlies rhyolite, from which it is partly derived, and it rests against the steep eroded base of the limestone mountains. The material is evidently waterlaid. The same formation stretches southward and is visible near Tj^bo as a strip of yellow dissected hills. At the pass between the Hot Creek Range and the Kawich Range are large amounts of horizontally stratified white waterlaid deposits composed of rhyolitic fragments.'^' This formation is evidently the same as described in the neighbor- hood of Twin Springs, in the Pancake Range, a few miles to the east. aThis formation is chiefly included under the color for volcanic rocks on the map. The nar- row atrip near Tybo is not represented. spuRR.J HOT CREEK RANGE. 87 IGNEOUS ROCKS. The whole north end. of the Hot Creek Range, beginning with a point a few miles north of Hot Creek, is, so far as known, composed entirely of volcanic rocks, including both rhyolite and basalt. There has been much erosion since the outpouring, resulting in the carv- ing of considerable valleys and the formation of large gulch dumps (alluvial fans) at their mouths, exactly as in the case of the stratified rocks. In jilaces, also, erosion has stripped away the upper layers of lava and ash and has exposed symmetrical volcanic cones, which have been preserved by this protecting covering. PI. V, .B, is aphotograi)h of such a cone. The number of these small cones and the abundance of ash, together with the thinness of the lava sheet, show that the volcanic rock in this region came from many separate explosive vents. In the neighborhood of Hot Creek, as before stated, the eastern half of the range contains a considerable area of Silurian rocks. However, rhyolile is found at the extreme eastern base, and the whole western half of the mountain at this point is composed of several thousand feet of the same rock. From here to the southern end of the range the western part is of volcanic, while the eastern half is mostly strat- ified. At the southern end the rh3^olite mantles around to the east to join the lava of the Kawich Range. STRUCTURE. In Hot Creek Canyon the Silurian rocks form an anticlinal fold, broken by two or three normal easterly dipping faults. The first of these faults occurs at the eastern end of the canyon, and by it the strata, including the P^ureka quartzite, are down-fanlted to the east 200 or 300 feet. This fault was also noted in the first canyon south of Hot Creek. Three miles farther west occurs a second parallel fault. This fault has a vertical separation of about 1,000 feet, as marked by the Eureka quartzite, upthrown on the west. (See fig. 7.) From Hot Creek to the southern end of the range the structure was not carefulljr examined, but for nearly the whole way the limestones can be seen to dip in general westerly at an angle of from 15° to 20°. It is probable that this dip represents the westerly limb of the anti- clinal fold exi:)osed in Hot Creek Canj^on. ORES. Along Hot Creek Canyon are some vertical zones in which rich pock- ets of ore are said to have been found. These zones are apparently ancient channels of the hot springs, which still exist. South of this jDoint the rocks are more or less mineralized all the way toTybo, where there are some important ore deposits. GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. ^sauQ-^offl Sz^udff 'zuunjA 1 I m O t3 ^ T3 e OJ P '« "S ii F^ 02 t> 6» -S .-s o J? N -St; -g O '3 p s 2 ^ O g 0) bo O !h O J? P PINON RANGE. The Pinon Range is mentioned in this report only because its southern end, wliieh extends beyond the south- ern limit of the Fortieth Parallel maps, is included in the accompany- ing map. The writer did not visit this range, and the following slight summarj^ is taken chiefly from the work of the Fortieth Parallel geol- ogists. TOPOGRAPHY. The range consists of a single main ridge, which is conspicuous north of the fortieth parallel and lies next west of the Humboldt Range. Far- ther south the Diamond Range comes in between the two. Near this x)oint the Pinon Range becomes lower, and its trend changes from south to south- easterlj^ so that it swings around and joins the Diamond Range near Eureka. SEDIMENTARY ROCKS. In the neighborhood of Pinto Peak there is exposed a thickness of about 14,000 feet of sedimentary rocks, ^ comprising a section from the Cam- brian up into the Carboniferous. South of this the range is almost en- tirely composed of Devonian rocks. These Devonian rocks are continu- ous southward to the junction with the Eureka Mountains.*^ IGNEOUS ROCKS. VOLCANIC ROCKS. Throughout most of the extent of the range various volcanic rocks are found, both at the east and the west bases. "Arnold Hague, U. S. Geol. Expl. Fortieth Par., Vol. II, p. 554. ''Arnold Hague, Geology of the Eureka district: Mon. U. S. Geol. Survey Vol. XX, p. 300. SPUKK] PINON, MONITOR, AND WALWEAH RANGES. 89 STRUCTURE. As stated by Mr. Hague/' the range consists of open anticlinal and s.vnclinal folds. South of Pinto Peak the structure is anticlinal, the axis of the fold striking diagonally across the range S. 25° E., while the general trend of the range at this point is west of south. It is likely that the main anticlinal fold of the Diamond Range is the direct continuation of this anticline. Farther south, along the Piiion Range, this anticline gives way to an adjacent sjnicline, and farther south again the eastern limb of this s^nicline is cut off by the ^"alley, so that only the western or easterl}^ dipping limb remains. This por- tion of the range, therefore, has the aspect of being monoclinal. A section made b}^ Mr. Walcott,* at Ravens Nest, just north of Pinto Peak, shows the structure as a faulted anticline. MONITOR RANGE. The Monitor Range is a belt of mountains about 70 miles long, Ijdng next west of the Hot Creek Range. It has its northern end just south of the area shown on the Fortieth Parallel maps. The northern part of the range, up to within a few miles of Altoona Pass, has the aspect of a great west-sloping table which ends in a scarp on the west, facing the vallej^. At Altoona Pass the range is narrower and has a very sharp summit, with a steep descent on both sides. Farther south the range grows lower and is broken b}^ frequent gaps, till it passes into low volcanic hills and dies out in the Ralston Desert. Gilbert^ has observed a single spur of metamorphic rock on the west side of the range at its southern end. Otherwise the whole southern part of the range, as observed by Mr. Gilbert and the writer, is vol- canic. At Altoona Pass the lava is a siliceous rhyolite like that of the Hot Creek Range. It is probable that this range has been formed b}^ a series of vol- canoes along a north-south line. The topograph}^ of the southern part of the range (like that in the southern parts of the Toquima and Pancake ranges) is extremel}" irregular, consisting in part of inter- rupted mesas and ancient volcanic cones defaced by erosion. It is plain from this topography that the lavas have escaped from many different vents and have flowed together. Erosion of the lava has gone on to a considerable extent, indicating the lapse of some time since the cessation of volcanic activitj-. WAHWEAH RANGE. The name Wahweah Range is applied to an irregular cluster of hills west of the southern end of the Piiion Range and just witliin the "U.S.Geol. Expl. Fortieth Par., Vol. II, p. 5.51. * '' Men. U. S. Geol. Siirvey Vol. XX, p. 2(11. e\J. S. Geog. Surveys W. One Hundredth Mer., Vol. Ill, p. 121. 90 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. -08. northern limits of the accompanyiDg map. It was not visited bj^ the writer, and the following brief characterization is taken from the reports of the Fortieth Parallel Survey: The range is about 30 miles long and at its northern end consists mainly of granite, together with a heavy body of qnartzite, which was referred to the Ogden Devonian on lithologic grounds, there being no fossils. The sedimentary rocks are here flanked by flows of volcanics, which farther south mantle over the stratified rocks and constitute most of the surface, exposingthe underlying Paleozoic only in patches. '^ TOQUIMA RANGE. The Toquima Range is situated next west from the Monitor Range. It has a trend a little east of north and a total length of about 80 miles. At its north end it passes into the level desert east of Austin, and its south end is situated southwest of Belmont, on the borders of Ralston Valley. The San Antonio Mountains are an irregular clump, south of the Toquima Range, and ai-e separated from this range by a gap only a few miles wide. Thej^ are surrounded on all sides by detritus-covered plains. TOPOGRAPHY. The Toquima Range has comparatively great relief. In general it consists of a single ridge of moderate breadth. At its southern end, near the town of Belmont, this splits in two, the main ridge trending : a little west of south toward the San Antonio Mountains, while a minor one diverges and runs in a southeasterly direction into the Monitor Range. Between the two ridges is a low valley, filled with Pleistocene detritus. The range is essentially volcanic, but in places is ex]30sed a core of Paleozoic rocks beneath, indicating that here, as in the Hot Creek Range, the Antelope Mountains, and others, there existed a distinct range of Paleozoic rocks before the lava efi'usion, which has now almost completely masked the stratified rocks and given the range the aspect of being primaril}' volcanic. SEDIMENTARY ROCKS. • The range was crossed by the writer only at one point. His route lay from the town of Belmont, around the southern end of the range, along the road to Cloverdale. Along this route no stratified rocks could be seen in the range. North of Belmont all is apparently vol- canic. This impression has been confirmed by reconnaissance notes made bj'^ Messrs. Gilbert* and Emmons.^ Mr. Emmons suggests that (I U. S. Geol. Expl. Fortieth Par., Vol. II, p. 566. - ' '> U. S. Geol. Surv. W. One Hundredth Mer., Vol. Ill, p. 121. cU. S. Geol. Expl. Fortieth Par., Vol. Ill, p. 393. SPURB.I TOQUIMA EANGE. 01 the core of the range some distance north of Belmont may be com- posed of stratified rocks, hut the first point where they have been observed is just east of Belmont, where occurs a series of black limy slates and gray finely crystalline limestone, banded black and white, and often siliceous. The formation is preeminently a slaty one and has often the aspect of a schist. This aspect is due to metamorpliisin, occasioned by certain siliceous dikes of the granitic family. One great dike is half a mile wide and runs in a north-south direction. Near its junction the shaly limestones become transformed into jas- peroid, and in places by the development of mica the rock j)asses into mica-schist. Some of the jasperoid is also schistose, and contains small bunches of red and j^ellow metallic oxides, which give it the asj)ect of a knotted schist. The stratified rocks here are tilted at high angles. Where observed by the writer they were mostly vertical, but Mr. Emmons found a general easterlj" dip. In the slates Mr. Gilbert '^ found graptolites, which referred the rocks to the Silurian age. According to Mr. Walcott,'^ the rocks prob- ably correspond to a i)art of the nj)per Pogonip formation of Eureka. Mr. Gilbert^ estimates the apparent thickness of the stratified series at Belmont at 4,000 or 5,000 feet. On the road leading from Belmont southwest toward Cloverdale the same series of strata is found at the eastern base of the main ridge. The chief rock is compact limy black slate, often metamorphic and schistose, corresponding closelj^ with the rocks just east of Belmont. The metamorphism is evidently, as in the former case, connected uith intrusive masses of granite and rhyolite. By these the slate is some- times transformed into an unsheared jasperoid or to a quartz-schist (the latter often containing actinolite and staurolite) and sometimes into highly crystalline mica-schist. A mile south of the most north- ern outcroj^ found the shales are overlain bj^ about 200 feet of massive white quartzite, which is probably the Eureka formation. The quartz- ites and underlying beds are exposed south of here for some distance till they disappear under Pleistocene detritus on one side and volcanic rocks on the other. Farther southwest, however, at the spring, is found another small patch of the schistose slates capped by the quartzite. This patch is surrounded on all sides by rhyolites, and is chiefiy altei-ed into jasperoid seamed with iron. Looking eastward from the eastern base of the main ridge a portion of the minor ridge which runs southeasterly from Belmont is seen to be composed of stratified rocks similar to those just described. Aj)par- ently the schists and the overljang white quartzite can be recognized. a U. S. Geol. Surv W. One Hundredth Mer., Vol. Ill, p 180. i-Mon. U. S. Geol. Survey Vol. Vm, p. 2. "•■Op. cit., p. '.jH. 92 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. IGNEOUS ROCKS. The whole northern part of the Toquima Range appears to be cov- ered up by great flows of rhyolite. Just east of Belmont the foothills bordering the area of stratified rocks are composed of rhyolite running out to the north toward the main mass. Rhyolite is also found in large quantities southwest of Belmont. This area stretches north and, growing broader, joins the great mass whicli covers the northern part of the range. To the south also it appears to stretch across the gap to the San Antonio Mountains. Similai^ly, the rocks of the minor ridge which runs southeast from Belmont are mainly rhyolitos, form- ing a continuous body with the rhyolites of the Monitor Range. DIKE ROCKS. Near Belmont there is a considerable development of coarse-grained granitic rocks. In several cases these are found to be intrusive into the stratified I'ocks. A mile south of Belmont is an exposure of coarse granite-porphyr}^ with sparse biotite and numerous large orthoclase phenocrysts from 2 to 4 inches long. This may be continuous with the great dike before noted as running north and south just east of Belmont and having a width of half a mile. The rocks of this dike, however, are different, being finer grained and in general more siliceous. They consist chieflj^ of quartz and feldspar. In, some places the rock becomes mostl}^ quartz; in others mainlj^ feldspar. Quartz veins are abundant, irregular, and segrega- tional, and evidently are the results of crystallization contempora- neous in a general way with the- crystallization of the rest of the rock. Biotite is often sparsely present, and in some x^laces the rock contains considerable muscovite and even passes into muscovitic quartz veins. Thin sections of the rock examined show in one case a fine-grained biotite-quartz-raonzonite; in another case siliceous muscovite-biotite- granite, peculiar in having certain areas entirely of quartz. This rock is evidently closely related with another which is essentially composed of quartz and muscovite, Avith a little albite. This is a variation of the muscovite-biotite-granite, in which muscovite has largely taken the place of feldspar. The distinction between this type and the micaceous quartz veins which occur in close connection with it, is not sharp «. STRUCTURE. The Silurian shales which occur just east of Belmont have a strike of N. 35° W., and change from vertical to a generally easterly dip. Southwest of Belmont, on the eastern side of the main ridge, the same a J. E. Spurr, Quartz-muscovite rock from Belmont, Nev.: Am. Jour. Sci., 4th series, Vol. X, 1900, p. 351. SPURR] TOYABE RANGE. 93 rocks luive a general uortli-soutli strike and a westerly dip of 20°. The two locations, therefore, may be on the two limbs of an anticli- nal fold. The fnrther strnctni-e of the stratified rocivs is concealed beneath the lava flows. ORES. In the vicinity of Belmont there has been considerable ore dei^osi- tion, which in the time of Nevada's prosperity made the region one of considerable wealth. At present the mining indnstry is perfectly dormant. During the period of activity the region was described by Mr. Emmons." According to him the ores occur generally in white quartz veins, often several feet in width, and consist princij)ally of stetefeldtite (an argentiferous ore of antimony) with which is com- bined lead, silver, copper, and iron. The metallic minerals are scat- tered through the quartz in bunches or disseminated particles — rarely in banded form. The veins are found cutting the Silurian shales and limestones, and frequent!}' are close to tlie intrusive granitic dikes. It appears to the writer that there is a genetic connection between the intrusive rocks and the inetalliferous quartz veins of this dis- trict. ^ TOYABE RANGE. The Toyabe Range lies next west of the Toquima and extends south- ward about the same distance. To the north, however, it has a greater length, running along the western border of the desert into which the Toquima Range merges at its northern end. Thus the entire length of the Toyabe Range is about 100 miles. It lias a uniform north - northeast trend. That portion of the Toj^abe Range which lies north of Austin has been included in the general maps of the Fortieth Parallel Survey. From Austin southward nearly to the southern end of the i^ange, the mountains have been made the subject of a special study by Mr. Emmons. '■ The writer observed the range at its extreme southern end, and also its western base, along the valley which separates it from the closely adjacent Reese River Range. TOPOGRAPHY. The topography of the Toyabe Range is marked by features of con- siderable contrast, the mountains being sharp and high and the inter- vening canyons deeply cut. Throughout most of its course the range consists of a single ridge in its central portion. The southern ends of this range and of the Reese River Range converge until they almost unite. The southern part of the range is essentially volcanic; while the rest is composed chiefly of granite and Paleozoic strata. The erosion «U. S. Geol. Expl. Fortieth Par., Vol. Ill, p. 393. & J. E. Spurr, Am. Jour. Sci., 4th series, Vol. X, 1900, p. 365. cQp. cit., p. 320; Atlas. PI. XIII. 94 GEOLOGY OF NEVADA SOUTH OF ■iOTH PARALLEL, [bull. 20; of the lavas appears to have been quite as profound as that of the stratified rocks, showing that a considerable period has elapsed since the effusion of volcanic material. In the valley which separates the southern end of the Toyabe Range from the corresponding portion of the Reese River Range there is a higli divide, separating the north-flowing drainage of Reese River from that which flows south into the desert plain at Cloverdale. The south-flowing drainage runs in a canyon cut into the bottom of the valley, with rhyolite walls which go up at angles of from 45° to 65° to heights of 700 or 800 feet. At its bottom is a level floor covered with wash and sagebrush, and in the center of this floor is an arroyo 5 or 6 feet deep. At Cloverdale this bottom is one-quarter of a mile across, while 7 or 8 miles up it is barely 30 yards. The stream which flows in this canyon is derived from a spring. This case is like one described in the Snake Range region. Another noteworthy feature of the erosion of this range, according to Mr. Emmons, is the occurrence of basins at the heads of some of the canyons, which basins, he infers, were formerly occupied by glaciers. At the mouth of one of the canyons Mr. Emmons "• found glacial strige, which strengthened his belief. On most of the Great Basin ranges, as is well known, there are no marks of glaciation. SEDIMENTARY ROCKS. CAMBRIAN. All the stratified Paleozoic strata of the Toyabe Range were mapped by the Fortieth Parallel geologists as Carboniferous, since (^arbonif- \ erous fossils were the only ones found in the series. These occurred in limestones. Beneath the limestones was a thick series of slates, which were regarded as the same as those in the Toquima Range near Belmont. The subsequent finding by Mr. Gilbert of fossils in the Belmont slates determined them as Silurian. Beneath these slates, in the Toyabe Range, Mr. Emmons has described a series of compact white quartzites with some thin beds of white gi-anular limestone, the series being several thousand feet thick. The quartzites underlie the slate series in apj)arent conformity, and outcroi) in places along the eastern face of the south half of the range. Farther north, beyond Austin, the high mountain called the Dome has been described by Mr. Hague ^ as consisting of nearly white quartzite beds, which seem to be bent into a broad anticlinal fold. These are overlain by beds of siliceous and argillaceous slates, and these by compact gray limestones. This is evidently the same series as described by Mr. Emmons. The thickness of the quartzites is not estimated, but must be great. a U. S. aeol. Expl. Fortieth Par., Vol. Ill, p. 328. bldem, Vol. II, p. 630. SPURR.] TOYABE RANGE. 95 No fossils were found in tliese quartzites, but in the Eureka section no such quartzite exist except that of the basal Cambrian; and the position of this series in tlie Toj^abe Range above probable Silurian slates strengthens the belief that it also is Cambrian. SILURIAN. As before noted, Mr. Emmons has described, overlying the heavy quartzites, an estimated thickness of 7,000 feet of limestone shales, with siliceous clay slates, locally metamorphosed into schistose rocks. Mr. Emmons regarded these slates as the same as at Belmont. In these latter rocks Silurian fossils have since been found. In the Eureka section the thickness of the Silurian is estimated at 5,000 feet. This slate series occupies the central portion of the ranee, the gen- eral structure being anticlinal. DEVONIAN. Whether or not the Devonian exists in tliis range is not certain. The i3resence of Carboniferous and probable Silurian makes it seem veiy possible that the Devonian also conies in, although it has not been" recognized. CARBONIFEROUS. Overljdng the slate series which has just been referred to the Silurian, Mr. Emmons "' has described a compact dark-blue limestone which lies conformably upon the slates and is exposed on both flanks of the range on the two sides of the general anticlimil fold which is the chief structural feature. In this limestone. Mr. Emmons found Fusiilina cylindrica and 8yri7igopora. TERTIARY. Near the northern end of the range Mr. Hague ^ has described, beneath i-hyolite, beds of volcanic ash which, although without deter- minable fossils, he referred to the Miocene. These beds are older than the rhyolite and have been disturbed, since their deposition, by the intrusion of igneous rocks, so that they underlie unconformably sup- posedly Pliocene strata, which are younger than the rhyolite. IGNEOUS ROCKS. A considerable portion of the Toyabe Range is made up of granite and volcanic rocks. Mr. Emmons^ has described five bodies of granite, all intrusive into Paleozoic strata. The rocks vary somewhat in texture and composi- tion, but are generally markedly siliceous, being characterized by a aU. S. Geol. Expl. Fortieth Par.. Vol. Ill, p 3^3. 6Idem, YqI-, II. ?■ 6^^ "^V- cit., p. 324. 96 GEOLOUr OF NEVADA SOUTH OF 40TH PARALLEL, [bull.308. large ijroportiou of quartz, an almost entire absence of hornblende, and a small j)roportion of mica. Associated with the granite are fine- grained dikes. RHYOLITE. Volcanic rocks occur at intervals along the flanks of the range, but the most important mass is at the southern end, where for 30 miles it completely conceals the granite and the stratified rocks. Among the volcanic rocks, rhyolite is the only one that lias any very wide distribution, so far as observed. Mr. Emmons notes tliat rhj^olite occurs in exceptionally large masses and is of comparatively uniform coarse texture, having a granitic a^jpearance in tlie hand specimen. At the southern end of the range the present writer has studied the rhyolites, which are here associated with tuffs. The gen- eral type is biotite-hornblende-rhyolite, similar to the lava which forms the southern end of the adjacent Toquima Range. AUGITE-BASALT. In the little valley which separates the southern end of the Toyabe Range from the Reese River Range there was found, near the head of the Reese River drainage, a small area of augite-basalt. RELATIVE AGE OF THE IGNEOUS ROCKS. As in the Toquima Range, the intrusive granites of the Toyabe Range and the rhyolites show marked consanguinity in composition. ; Each is characterized by biotite as the chief ferromagnesian mineral. The augite-basalt is decidedly younger than the rhyolite, since it ' was poured out in a valley which has been deeply cut into the latter rock. STRUCTURE. According to Mr. Emmons « the range owes its existence chiefly to a lateral compression, which has thrown the stratified rocks into north-south anticlinal and synclinal folds. In addition to this there has been another pressure, coming from a different direction, which has distorted and dislocated these folds. The main fold of the range is an anticline, which occupies the whole central part of the range. The axis of this fold has an extreme variation from northeast at its northern end to northwest at its southern. South of here, at Ophir Canyon, Mr. Emmons noted a syncline, probably adjacent to the main anticline. This syncline, however, was probably formed by the intrusion of granite. To the north of the central part of the range, in the vicinity of Austin, another synclinal fold appears, which also seems to be connected with a granitic intrusion. Farther north, aXJ- S. Geol. Expl. Fortietli Par., Vol. Ill, p. 326. SPURR] TOYABE KANGE. 97 as stated, the striictiive of the high mountain called, the Dome appeared to Mr. Hague "^ to he anticlinal. ORES. Formerly the ores of the Toyabe Range were of great economic importance, but with the decline of the mining industries of Nevada they have been almost forgotten. The principal mining region was in the neighborhood of Austin, but mines were found from here south- ward all along the range. Mr. Emmons has described many of the deposits, which in nearly ever}^ case consist of veins of white quartz carrying metallic sulphides in irregularly disseminated bunches and streaks. In the vicinity of Austin, the oldest mining district in the State, the veins are mostly in granite, and rich ores do not appear to occur in other rocks. In other parts of the range, however, the veins occur in the stratified rocks. Besides quartz as gangue mineral, man- ganese spar and calc spar were noted, while the metallic sulphides comprise proustite, pyrargyrite, stephanite, polybasite, tetrahedrite, argentiferous galena, zinc blende, copper pyrites, and iron pyrites. In some of the veins the chief silver-bearing mineral is a mixed sul- phide of antimony, as is the case in the neighborhood of Belmont. The veins are often faulted. As in the case with the ores at Belmont, there is probably an inti- mate connection between the metalliferous quartz veins and the intrusive rocks. aU. S. Geol. Espl. Fortieth Par., Vol. II, p. 630. Bull. 2U8— U3 7 CHAPTER II. KAISTGES OF WEST-CKISTTRAL ISTEVADA. REESE RIVER RANGE. The Reese River Range lies next west of the Toyabe Range, from which it is separated only by a narrow north-south valley at its southern end. From here it extends in a direction a little east of north about 100 miles into the area of the Fortieth Parallel surveys. Farther north the same general line of elevations is continued in the Shoshone Range. TOPOGRAPHY. So far as' observed, the Reese River Range is composed entirely of igneous rocks, and the forms produced by erosion have therefore a certain uniformit3^ The summits show peaks which resemble rem- nants of ancient volcanic cones, and the valleys which furrow the flanks are deeply cut. The valley which sepai-ates the Reese River Range from the Toyabe Range at its southern end has considerable interest. Its broad rounded form, as contrasted with the sharp incision of the lesser mountain valleys, shows that it has not been jDroduced since the effusion of the lavas, but existed previously; yet the bottom of the valley consists of an unknown thickness of lava, similar to that of the mountains on both sides. Subsequent to the iDcriod of effusion, erosion has formed deep gorges in the valley bottom. Fifteen miles north of the southern end of the Reese River Range there is in the valley a divide which separates the northward-flowing drainage of Reese River from that which runs south. The southward- flowing drainage is in a canyon which is cut below the main valley floor 700 or 800 feet.® On the north side of the divide, the descent is sharp into a broad, V-shaped valley cut in the rhyolite. Farther north, where the mountains diverge, the valley suddenly widens, and at the same time the topography of the base of the mountains on both sides changes, a broad, gently sloping plateau taking the place of the irregular hill topography of the higher valley. In the middle of this plateau the valley in which the uppermost drainage of Reese River flows is several miles wide. a See p. 9i. 98' SPURK.] REESE EIVER AND ELLSWORTH RANGES. 99 IGNEOUS ROCKS. So far as seen, the range is composed mainly of great masses of rlij^olite, similar to the lava wliicli makes np the southern end of the Toyabe Range. Along the eastern base of the mountains, at their southern end, are abundant dejjosits of white volcanic ash. The erup- tions whieli poured out the lava must, therefore, have been of an explosive nature. In the valley between the Keese River Range and the Toyabe Range, at a point southeast of lone, a flow of augite-basalt was found. On the opposite side of the range, in the vicinity of lone, there is a considerable body of the same rock. On the edge of the desert valley, 1 or 2 miles west from lone, there is a basic lava which appears, upon microscopic examination, to be biotite-andesite. The low ridges running south from Cloverdale to the Monte Cristo Mountains are mainly flat volcanic mesas. As seen from tlie vicinity of lone, the Reese River Range for 10 or 15 miles north is evidently volcanic, and is x)robably mainly so up to the junction of the Fortieth Parallel maj), where the Shoshone Range is represented as all rhyolite. AGE OF LAVAS. The augite-basalt on both sides of the range is plainly younger than the rhyolite, and appears to lie against the flanks of the hills eroded from it. ELLSWORTH RANGE. The name Ellsworth Range is here applied to the extreme southern end of a series of rather disconnected ridges which farther north are known as the Desatoya Mountains. This southern end, so named from the decayed mining camj) of Ellsworth, is narrow, and consists of a single ridge which reaches a moderately great altitude. In general the range seems to be composed of an ancient series of volcanics and derived tuffs, Avith limestones. These are cut by dikes and are capped and often entirely hidden by late volcanic flows. SEDIMENTARY ROCKS. The range was crossed by the writer between Ellsworth, on the east side, and Downieville, on the west. On the road some miles west of Ellsworth is a comparatively small outcrop of white granular lime- stone, consisting of loosely cohering calcite crj^stals, which give a granular appearance not unlike that of sandstone. This rock is asso- ciated with an altered green rock of probable igneous origin, which is cut by siliceous dikes and is frequently mineralized. The only specimen of the green rock examined turned out to be made up of epidote, quartz, and calcite, all probably secondary and resultant 100 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 308. from alteratiou accompauying the introduction of tlie metallic sul- phides which are frequently found disseminated in the rock. On the summit of the pass, separated from the locality just men- tioned by a sheet of overlying basic lava, there is found, immediately beneath the volcanic rock, a dense sandstone or tuff, which on micro- scopic examination is found to consist of rounded quartz grains and altered feldsj^ar fragments. This tuff contains occasionally angular fragments of lava and also doubtful x^lant remains. From here to the foot of the comparatively steep scarp which occurs along the western face of the range, there is a vertical distance of nearly 2,000 feet. The section shows a single rock series, all prob- ably of igneous origin. The rocks are reddish or greenish, often trap like and nearly always contain abundant angular fragments of lava, giving" the ajDpearance of a breccia. Rock having the appear- ance of red sandstone is common, but when examined under the micro- scope this is found to consist chiefly of highly altered feldspar frag- ments, with some calcite and epidote, the whole being stained with iron oxide. It is probable, therefore, that this rock is also a volcanic tuff. More abundant than this ajjparent red sandstone is a dense, greenish-looking rock, which microscopic examination shows to be probably a hornblende-biotite-syenite-porphyry. Below the chief mass of this igneous rock there is again found a great thickness of f eldspathic tuff, which is highly colored in the hand specimen. Under the microscope the tuft" is seen to be made up of rounded and broken fragments of feldspar in a kaolinic matrix, the whole colored by iron oxide. Below this again there is found white volcanic tuff, resem- bling ash, but containing some rounded, apparently waterworn, grains. The dij) of this series of igneous rocks and tuffs seems to be in gen- eral to the west, although the folding on a small scale is considerable. At the base of the abrupt mountain scarp is found a moderately thin-bedded siliceous limestone, without fossils. The general strike is north and south, and the dip 20° to 30° W. This rock is found continuously to the end of the foothills at Downieville, where dark- blue limestone alternates with beds of white and gray granular limestone or marble. In the whole series exposed in the Ellsworth Range no fossils were found, except in the limestone just east of Downieville, where they were too poorly preserved to warrant collection. The marble or white granular limestone at Downieville resembles that described on the east side of the mountain, above Ellsworth. In both places there is a north-south strike. The dip in the occur- rence near Ellsworth is an easterly one of 4°, while near Downieville it is westerly, averaging 20° or 30°. It may be, therefore, that the two occurrences are on opposite sides of an anticlinal fold. If this is the case, then the thick series of interstratified igneous rocks and SPURR.] ELLSWORTH HAISTGE. 101 tuffs wliicli constitutes the core of tlie mountain lies beneath the limestone series. The volcanic series must be at least 2,000 feet thick, the limestone series hardly less. If we had no other data than the preceding we would hardly be able even to suggest the age of the rocks. We have, however, from the researches of the Fortieth Parallel geologists, in the region not far north, results which may help us in correlating. In this same range near New Pass Peak, about 60 miles northeast, are Triassic strata which Mr. Emmons has described in the following terms'' : The lowest exjiosiires show strata of a greenish, somewhat cherty qtiartzite. Above these, forming the summit of the ridge, is a breccia-like conglomerate, made np of greenish and purple clierty fragments, with a red cement, overlaid by a thickness of abont 1,000 feet of qnartzite and conglomerate, weathering with a peculiar yellowish-brown earthy surface. On the western slopes, imme- diately miderlying the limestones, is a bed of purple, argillaceons roofing slate. As exposed in Ammonite Canyon, there lies conformably above this a thickness of 1.000 to 1,500 feet of dark grayish-bine, compact, earthy limestones of the Star Peak grotip, which lithologically can not be distingiiished from the Car- boniferous limestones. At the contact of the limestones with the qnartzites is a band of yellow calcareous shales. The underlying greenish cherty quartzite and breccia-like con- glomerate with red cement, described by Mr. Emmons, recalls the central mass of tuffs and volcanic rocks near Ellsworth, while the overlying, dark grayish-blue limestones are similar to those near Downieville. Immediatel}^ above the limestones Mr. Emmons found abundant Triassic fossils in a series of shales which were not observed in the Downieville section The lower of the two series at l^ew Pass Peak has been correlated by Mr. King with the Koiijar.o formation, and the underlying lime- stone with the Star Peak formation, both formations occurring in the Triassic of West Humboldt Range. Concerning the Koipato in the West Humboldt Mountains, Mr. King writes that at the base it consists of a vast thickness of quartzitic and argillaceous beds. These purely sedimentary rocks are observed to i3ass lateral^ into a rock which in hand specimens resembles an eruptive rock. This whole series contains no distinct beds of limestone, and wherever analyzed is remarkably free from carbonate of lime. Its lower limit is nowhere seen and, owing to the disappearance of the strata planes nnder extreme metamoi-phism, there is no possible mode of arriving at its total thickness. The upper limit, however, is sharply marked by an abrupt transition from the schists into a body of dark carbonaceous limestone. To this whole underlying group of schists and porphyroids we have given the title Koipato. from the Indian name of this range.'' Allowing for some slight difference in interpretation, Mr. King's characterization of the Koii)ato formation applies to the rocks on the western face of the range between Ellsworth and Downieville. Mr. King believed that the transition from sedimentary argillites to « U. S. Geol. Expl. Fortieth Par. , Vol. II. p. 644. 6 Idem, Vol. I, p. 2H9. 102 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. igneous rocks resulted from metamorphism, while in the case of the rocks near Ellsworth those which possess igneous structure are almost without doiTbt ancient volcanics, which pass above and below, and probably laterally, into shales, conglomerates, and water-laid brec- cias derived from these or similar igneous rocks. The whole series therefore is conceived to represent the products of a period of ancient volcanic activity. The series is more indurated, altered, and oxidized than any of the Tertiary volcanic series, and no similar rocks 'are known in the Paleo- zoic of Nevada. Their correlation with the established Triassic for- mations is therefore j)lausible. IGNEOUS ROCKS. The oldest igneous rocks of the range are those just described as interstratified with the tuffs of the great ancient volcanic series. The only specimen examined is probably a hornblende-biotite-sj^enite- porphyry. Next younger than these ancient. volcanics come siliceous dikes, which are well exposed on the eastern face of the -range, near Ells- worth. The most easterly outcrop encountered is an alaskite-por- phyrjT^ "■ containing feldspar phenocrysts which are sometimes as much as 4 or 6 inches long. This resembles the granitic rock described south of Belmont. It is cut b}^ several narrow dikes of liner-grained rock having the same composition, but not porphja'itic. These silice- ous dikes are intrusive into metamorphosed green rock just west of Ellsworth, the siliceous rock cutting the other in numerous dikes. Covering the ancient volcanic rocks and the later alaskite dikes there is found, occupying the center of the mountain between Ells- worth and Downieville, a bed of volcanic ash. Above this, forming the crest of the range and constituting all the high peaks, is a mas- sive, columnar-jointed volcanic rock. A specimen of this proved on examination to be hyperstheue-aleutite.^ In the western foothills, near Downieville, is also probably a patch of similar, comj)aratively young volcanic rock, and north of Downieville the low limestone mountains are succeeded after a few miles by a chain of lower hills, which are, in part at least, volcanic. These extend northward at least 10 or 15 miles. At the southern end of the Desatoya Range, as mapijed by the Fortieth Parallel geologists, the rocks are all volcanic, envelop- ing the Triassic strata exposed in the region of New Pass Peak. STRUCTURE. Apparentlj^ the main structure of the range is anticlinal, the ancient volcanic series constituting the core, from which the overly- a Alaskite is a general name proposed for rocks consisting essentially of quartz and alkali feld- spar, without essential ferromagnesian minerals. J. E. Spurr, Classification of igneous rocks according to composition: Am. Geol. Vol. XXV, 1000, No. 3. 6Aleutite is the name proposed for a rock intermediate between andesite and basalt. J. E. Spurr, Classification of igneovis rocks according to composition: Am. Geol., Vol. XXV, 1900, No. 3. 8PURR.] PILOT MOUNTAINS. 103 ing limestones dip away on both sides. Tnst north of Downieville the low limestone monntaius are separated from the main range by a shal- low and relatively broad valley. The structure of these low mountains is anticlinal, and between this anticline and the one comprised in the main ridge is a syncline, in which the intervening vallej^ lies. ORES. On both sides of the range there are ore deposits, once of great economic value, now largely abandoned. The mines near Ellsworth seem to be in the ancient igneous formation, and these old rocks show on exposed surfaces carbonate of copper and on fi-esh breaks copper pyi-ite. Between Downieville and the top of the mountains also there are ore deposits in the ancient volcanic series. At Downieville ores are found in the limestone, resulting apparently from replacement of the rock by sulphides. PILOT MOUNTAINS. East of the Excelsior Range, on the other side of Soda Springs Val- ley, lies a short but comiaaratively rugged mountain range which has a north-south trend, changing to northwest in its northern portion. On the south the foothills of this range merge into those of the Oan- delaria Mountains, and are separated from the northern end of the Monte Cristo Mountains only by a narrow gai3. On the north, the Pilot Mountains pass into the volcanic hills of the Galibs Valley Range. The highest portion of the range is Pilot Mountain, which lies just east of Sodaville. On the west face of this mountain there is a bold scarp (very likely a simple fault scarp), which rises from a point which has an estimated elevation of about 6,000 feet above sea level. Below this point there are immense gulch dumps, or alluvial fans, covering the other valley detritus, and reaching several miles westward toward the center of the valley. SEDIMENTARY ROCKS. ' EARLY TERTIARY OR MESOZOIC SERIES. Most of Pilot Mountain is made up of stratified rocks. At the base is a series of gray rocks which, on account of a slight east-west flex- ure, transverse to the general north-south line of folding, passes down to the north and south so as to be covered by the valley detritus. These rocks are hard to identify in the field on account of their altered character, but microscopic study shows them to consist mainly of vol- canic tuffs, generally coarse, sometimes fine and slaty. They grade into solid lavas. A specimen of one of the lava sheets on examina- tion seems to be andesite. In the field no sharp line can be drawn between the tuffs and the slaty lavas. These rocks are cut by many dikes of siliceous granite. 104 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL. [bull.2C(8. Overlying tliis gray tnffaceous series are reddish sandstones, shales, and conglomerates, which in tnrn are overlain by a considerable thickness of purer red sandstone and quartzite, which forms the sum- mit of the mountains. An estimation of the thickness of the different rock series in this section gives 1,000 feet for the basal tnffaceous series, 1,000 feet for the sandstone, shale, and conglomerate series, and also 1,000 feet for the purer red sandstone series, making a total of 2,000 feet of red sandstone, shale, and conglomerate overlying 1,000 feet of the gray tufifaceous series. Where the rocks immediately overlying the basal grsty series were examined at the base of the mountain they were found to be red or white sandstone and quartzite, sometimes fine and calcareous, some- times coarse and gritty. There is also much red sandstone con- glomerate, indurated and squeezed. The pebbles of the conglomerate seem to be entirelj^ of quartzite and chert. This reddish sandstone and shale series aj^pears to extend northward several miles, until overlain by later volcanic rocks. On the south it does not extend so far, being overlain in the foothills of the Pilot Range along the road between Sodaville and Columbus by later liorizontally stratified sediments. The upper 2,000 feet of red sandstone, shale, and conglomerate is perhaps the same series as that described as occurring in tlie Excel- sior Mountains, just across the valley to the west. The underlain g gray tnffaceous series is not found in the Excelsior Mountains. Litho- logically, some of the tuffs correspond to andesitic tuffs found in the folded Earlier Tertiary series of the Monte Cristo Mountains, 20 miles south of Pilot Peak. At the same time, the series has a verj^ strong lithologic resemblance to the supposedly Triassic beds of the Ells- worth Range, into which the Pilot Mountains are almost directlj^ con- tinuous on the north. Mr. H. W. Turner has recently reported Jurassic limestone and slate in the Pilot Mountains. " In a personal letter to the writer, Mr. Tur- ner states that at the north base of the mountains he found abundant fossils in limestone, which Avere examined by Prof. J. P. Smith, of Stanford University, who pronounced them certainly Jurassic. PLIOCENE. On the southern side of Soda Springs Valley, horizontally stratified rolled gravels were found at an elevation of about 5,250 feet, and were referred to the Pliocene sediments of Shoshone Lake. Similar sediments undoubtedly exist at the base of Pilot Mountain, but they have been covered ujp by the enormous subsequent Pleistocene gulch dumps, which form a belt along the foot of the mountain. The material in these dumps manifestly represents the larger portion of that removed from the gulches which cut back into the scarp of the inoun- oGeol. Soc. Am., Berkeley, Cal., Dec, 1900. Report in Am. Geologist, Feb., 1901, p. 133. spuRR] PILOT AND MONTE CRISTO MOUNTAINS. 105 tain above. The erosion of these g'lilches is, therefore, mainly Pleistocene. At the southern end of the Pilot Mountains, along the road between Sodaville and Columbus, is a considerable area of horizontally strati- fied fine silts and hardened clays, with some volcanic ash beds. This formation constitutes the divide between Soda Springs Valley and Columbus Valley, and reaches as high an elevation as 6,000 feet, where it is overlain by a sheet of basalt. These beds are evidently the result of deposition in a still bodj^ of water, and are correlated with the sim- ilar Pliocene beds described elsewhere in this region. IGNEOUS ROCKS. PLEISTOCENE OLIVINE-BASALT. At the southern end of the range, overlying probable Pliocene sedi- ments, occurs a thin-bedded, dark, vesicular lava, which proves to be olivine-basalt. From its occurrence there is no doubt that this rock should be classified with the other Pleistocene basalts of the region. GRANITIC ROCKS. Pilot Mountain contains many branching dikes and irregular masses of intrusive granitic rock, similar to that across the vallej^ in the eastern end of the Excelsior Range. A typical specimen, examined microscopicallj', proves to be a biotite-granite. The intrusives seem to be chiefly confined to the base of the mountain, and not to have reached, in veiy great quantity, the uppermost strata. The granite is accompanied hj alaskite,^' and in the vicinity of these intrusions are ore deposits, as in the case of the east end of the Excelsior Moun- tains; and the ore has probably had a genetic connection with the igneous rock. MONTE CRISTO MOUNTAINS. The Monte Cristo Mountains are comparatively short and low. The}" have a general north-south trend, and extend from the Pilot Mountains on the north to the Silver Peak Range on the south, with a total length of about 30 miles. SEDIMENTARY ROCKS. On the road between Columbus and Silver Peak there is a com- parativelj' low gap in the Monte Cristo Range. In this gap are found low hills of white shale capped by a porous bed which, examined microscopically, proved to be a calcareous andesite tufi". From this rock a collection of poorly preserved fossil shells was made, which Dr. W. H. Dall was not able to identify with cei-tainty. Dr. Dall thought the forms suggested a fresh-water origin. He found a a Rock consisting essentially of quartz and alkali feldspar, without essential ferromagnesian minerals. 106 GEOLOGY OP NEVADA SOUTH OF 40TH PARALLEL, [bull.208. bivalve, which may be a Sphcerium, and a gasteropod that may be a Planorhis. The shales contain frequent leaves and occasional coal seams. These sediments are capped by volcanic rocks. In the low pass above referred to the immediately overlying rock is a light-gray tordrillite. " Above this comes andesite. At the northern end of the Monte Cristo Range there appears to be a patch of stratified rocks similar to those just described, the inter- vening space being completelj^ covered by lavas. This series has been examined somewhat carefully by Mr. H. W. Turner, who has named it the Esmeralda formation. He finds that it is shown at various points in the Silver Peak Range, and that it comprises a considerable variety of sediments.* According to him the series exposed aggregates at least 2,000 feet, and is composed chiefly of sandstone, with some shale. The top is made u]3 of laeus- tral marls and white shales. Mr. Turner collected from these rocks fossil shells, fish bones and scales, and dicotyledonous leaves, which were examined by Dr. J. C. Merriam, Prof. F. A. Lucas, and Dr. F. H. Knowlton. Dr. Merriam lound that the fossil shells indicate an early Miocene or a late Eocene age for the beds, and Dr. Knowlton found that the plant remains indicate a Middle Tertiary age. The fish remains, so far as yet studied, do not seem determinate. The Avriter has observed in the region south of liere, notablj^ in the neighborhood of Death Vallej^ and in the Mojave Desert, upturned Tertiary sediments which he is inclined to correlate with the beds of the Esmeralda formation in the Silver Peak and Monte Cristo Mountains. IGNEOUS ROCKS. The greater portion of the Monte Cristo Mountains is covered by volcanic rocks. In general, dark basic lava seeuis to overlie lighter- colored siliceous lava. DESERT MOUNTAINS. The Desert Mountains form an irregular group which runs from the southern end of Mason Valley southeastward to near the north- western end of the Gabbs Yallej^ Range at the northern end of Walker Lake. In general these mountains have slight relief, although north of Mason Valley the peaks reach a considerable height. At the southern end the mountains change into low mesas of brilliant color. These mountains are composed entirely of well-bedded volcanic rocks. At the extreme northwestern end specimens examined prove to be biotite-hypersthene-andesite. Along the southeastern end, near "Tordrillite differs from a rhyolite in being more siliceous and containing no essential dark minerals. J.E. Spurr, Am.Geol., Vol. XXV, 19(10, No. 3. p. 230. bThe Esmeralda formation: Am. Geol., Vol. XXV, 1900, p. 168. sptTRR.] GABBS VALLEY AND GABBS VALLEY EANGE. 107 the liead of Walker Lake, the old beaches of tlie Pleistocene Lake Lahontan inay he traced. GABBS VALLEY AND GABBS VALLEY RANGE. Gabbs Valley is a broad, flat-bottomed basin, almost comi^letely sur- rounded by irregularly distributed volcanic mountains. The higher mountains to the south of the vallej^ constitute the Gabbs Valley Range, which extends from AValker Lake southeastward for about 40 miles to the Pilot Mountains. The topography of this range, as well as of the hills on the north side of the valley, is comparatively primi- tlA^e, the valleys being regular and in general not vei-y deepl}' cut, recalling the erosion topography of the sui3posedly I'liocene lake deposits of Pleasant Valley in the Snake Range. SEDIMENTARY ROCKS. EARLIER TERTIARY MARLS. Near the center of the valley, just east of the low mountain spur which crosses it, and on the Reese River road, there are low ridges of gi-ay, stratified marl containing leaf remains, alternating with gravels and more solid conglomerates. Some of the conglomerate contains comparatively alnindant silicified wood. The conglomerate, when examined microscopically, proves to be volcanic. The pebbles are made up in part at least of spherulitic glass. Some pebbles contain plienocrj^sts of feldspar, of species indicating that the lava is ande- sitic, in a glassy matrix containing broken feldspar and biotite. Some of the shaly beds associated with the conglomerate are felds- pathic tuff, made up of fine fibrous material, with larger In-oken frag- ments of feldsi^ar and some shreds of l)iotite. These beds strike north and south and dip about 8° E. No fossils were obtained from these beds. The locality is, how- ever, at a higher altitude than that of tlie Pleistocene lake which, according to Professor Russell,'^' covered tlie lowest part of the valley just west of here. Also, the beds seem to show a general tilting, and since, according to Mr. King,'''' the last marked folding in this area was j)ost-Mlocene, these beds are verj'- iikelj^ pre-Pliocene. They liave the aspect of lacustrine marls. Lithologically, they coincide with the descriptions given by Mr. King of his typical Truckee Miocene, which consists of sandstones, conglomerates, and tuffs at the base, witli an enormous thickness of volcanic tuffs at the top, the whole series being as much as 2,000 or 3,000 feet thick. The typical Miocene localities of King are situated near here to the north. Therefore the beds under consideration are provisionally^ correlated with those described b}^ Mr. King. They have also a general resemblance in their nature, derivation, degree of induration, and especially in their a Mon. U. S. Geol. Survey Vol. XI, PL XLVI. b XJ. S. GeoL Expl. Fortieth Par., Vol. I, p. 4.55. 108 G.EOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. containing silicified wood, with the early Tertiary series of the Silver Peak region, closelj^ adjacent to the south. (See p. 185.) PLEISTOCENE. In the lowest portion of Gabbs Valley, west of the Tertiary marls just described, is a broad alkali flat or playa, covered with smooth, hard mud. This was perhaps the bottom of a lake inclosed in the Gabbs Valley Basin. As mapped by Professor Russell, it was contem- poraneous with the great Lake Lahontan, but separated from it. At the base of the volcanic mountains there is a continuous apron of detrital material sloping away at an angle of about 3|° for a mile or two toward the middle of the basin. As in the case of the similar alluvial deposits investigated hj Mr. Russell,^' these aprons seem to be older than the great Pleistocene lakes. The effect of eolian action, of importance everywhere in the Great Basin, is very conspicuous in certain portions of Gabbs Valley. The Avind-blown sands have in many places accumulated in consider- able mass. IGNEOUS ROCKS. Most of the mountains surrounding Gabbs Valley, including the Gabbs Valley Range, are volcanic. These rocks represent a variety of species. Just east of the hot spring in the valley the road passes through a gap in the mountains about 1,500 feet deep, the sides of which rise at an angle of about 50°. The rock at this j)oint varies from moderately fine to moderately coarse, but it is, nevertheless, always holocrj^stal- line. It is massive and verticall}^ jointed, yet has a distinct horizon- tal bedding, and a little northeast of here it seems to be underlain by ash. It is therefore probably effusive. A single specimen of this rock, examined microscopically, proves to be a hornblende-biotite- quartz-monzonite. On the mountain ridge which separates Gabbs Valley from Walker Lake Valley the lavas which dip eastward into the former basin at angles of 10° or more, in color gray or oxidized bright red, prove to be biotite-, hypersthene-, and hornblende-aleutites and andesites. On all the mountains to the north of here, which were not visited, there appears to be a basal light-gray or red lava, which forms the highest peaks, underlying a dark-brown or black lava which forms the fringes of the mountains and sometimes constitutes a cone 3^et only slight]}^ defaced. Where tlie road crosses the extreme western end of the Gabbs Val- ley Range, overlooking Walker Lake, the lavas are mixed and the hills variegated, the colors being bright red, yellow, gray, greenish " Mon. U. S. Geol. Survey Vol. XI, p. 25G. SPURR.J EXCELSIOR RANGE. 109 yellow, white, and black. In geueral a liglit-gray lava is overlain by dense black flows. The former jiroved to be biotite-andesite, while the latter is augite-basalt. A little farther, biotite-rhyolite was found, api^arently underlying the basalt. EXCELSIOR RANGE. The name Excelsior Range is aj^plied to a short, rather irregular group of mountains which lies south of Walker Lake, and, unlike the most of the ranges of this region, runs in a general east-Avest direction, cutting off the southern end of Walker Lake Valley and extending from the southern end of the Walker River Range eastward to Soda Springs Valley. The entire length of the range is only about 30 miles. The main range has to the north of it several high spurs which run off at right angles and connect with a lower east-west ridge parallel to the main one, farther north. To the south also a number of north- south spurs connect the Excelsior Mountains with the Candelaria Mountains. The main range is terminated on the east by a bold scarp overlooking Soda Springs Valley, corresponding to the west- facing scarp of the Pilot Mountains on the other side. These mountains Avere crossed by the writer on the road between Hawthorne and Sodaville, which leads through Excelsior Flat. SEDIMENTARY ROCKS. LIMESTONE SERIES (EARLY TERTIARY?). If one travels along the above-mentioned road from Walker River Valley eastward, he finds, after passing through a belt of lava which constitutes the foothills, an area of thin-bedded, shaly, sometimes compact, blue limestone. This limestone is overlain by a lava sheet, and near the contact is baked and silicified to a greenish or brown jasperoid containing segregated nodules of silica. The stratification is nearly horizontal, but shows local contortion and horizontal fault- ing, suggested breaking and shoving by the overriding lava sheet. Near the contact, partly in the blue shaly limestone, partly in the same rock transformed into jasperoid by the contact metamorphism, were found fossils. Mr. T. W. Stanton, of the National Museum, reports on these as follows: Fossil lot No. 46, from the Excelsior Range, road between Hawthorne and Sodaville, evidently represents two distinct beds, one a hard brown siliceo-argilla- ceous rock and the other a dark-blue limestone. The former contains several specimens of a Corbula, another undetermined bivalve, and a very imperfect Gasteropod that may be a Natica or a Vivapar us,, th.Q generic character not pre- served. These are probably not earlier than Cretaceous, and they may be Tertiary. The blue limestone fragments yielded a small Neritina, a Hydrohia (?) , an Astarte (?) , and several imperfect specimens of two or three other small bivalves. These fossils have a Tertiary aspect. They are certainly not older than Cretaceous. 110 GEOI-OaY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.308. In answer to a query as to tlie conditions of deposition indicated by the fossils Mr. Stanton writes : The fossils in lot 46 are either marine or brackish-water form, not fresh water. If I could be sure that the bivalve I have called Astarte (?) really belonged to that genus there would be no doubt that they are marine. The other genera recog- nized live in both salt and brackish water. To the east tliis limestone forms a well-defined anticline, with a north-south axis, and with dips of 20° to 30° on both sides. Still farther east the limestone is again overlain by the volcanic rock wdiich encircles this area. In the bottom of Excelsior Flat, near its eastern side, probablj^ the same limestone series is found, but more altered and crushed and veined by dynamic action. Badly i^reserved fossils were collected from this rock, but could not be identified. The thickness of this limestone series was roughly estimated at 2,000 feet. SANDSTONE-SHALE SERIES (EARLY TERTIARY OR MESOZOIC?) . Along the western border of Excelsior Flat is found a belt of red sandstone which underlies the lavas. This sandstone belt is contin- uous to the low mountains south of here, where it passes upward into a series of gray vStratified rocks. Farther east the sandstone series, with the overlying gray rocks, seems to overlie the probable Tertiary limestones which outcroj) along the eastern portion of Excelsior Flat, the older rock being apparently the core of an east- west striking anti- clinal fold, and the sandstone series forming the northern limb. On the southern limb, which comprises the main ridge of the Excelsior Mountains, the bulk of the rocks seem, as viewed from a distance, also to belong to the stratified red sandstone and shale series. Following the road farther east, the transverse sjiur which runs northward from the main ridge of the Excelsior Mountains exhibits the same east- west striking anticline. Along the axis a canyon has been cut through the spur, and here are exjjosed red sandstones, with much red, yellow, brown, and green dense siliceous shales. No fossils could be found. The rocks here stand, in general, nearly vertical, and are crumj)led and faulted. South of here the rocks have a southerly dij), first steep, then shallowing, while to the north the rocks belonging to the same series have for a considerable distance a northerly dip, which afterwards reverses so that a body of underl3'- ing gray shale, which may belong to the probable Tertiary limestone series, comes into the visible section. From the data above noted, we appear to have a series of red sand- stones and quartzites, with some shales and conglomerates, having a roughly estimated thickness of 1,500 feet. These are overlain by a series of red -gray sandstones, shales, and conglomerates about 2,000 feet in thickness, making a total of about 3,500 feet. These rocks SPURR.] EXCELSIOK KANGE. Ill seem to overlie the probable Tertiary limestones aud are folded together with them. The exact contact of the tAvo series, however, was not found. No such sediments as this sandstone-shale are known in the Paleozoic section, and therefore the rocks would, without any other consideration, at once be considered as Mesozoic or Tertiary. In the region just south of here a series of folded shales and tuffs has been described by Mr. Turner" under the name of the Esmeralda formation and is probably Miocene, possibly reaching back into the Eocene. This series, when observed by the i^resent Avriter, struck him as resembling in a general way the thin sandstones and parti-colored shales of the Excelsior Range section, although the latter are dis- tinctly more highly indurated and altered. Rocks similar to the sandstone-shale series of the Excelsior Railge form a large portion of Pilot Mountain, just to the east of here, across Soda Springs Valley. As noted in the description of the Pilot Range, Mr. H. W. Turner found Jurassic fossils in some of these beds. It is therefore not certain whether the sandstones and shales of the Excelsior Mountains are Tertiary or Mesozoic, and they may be partly one and partly the other. While the series of tuffs, sandstones, shales, and conglomerates of the Excelsior Range may possibly be the equivalent of the somewhat similar strata of the Esmeralda formation near Silver Peak, the lime- stone of the former locality is not represented in the latter. This limestone also sejjarates itself from the probable fresh- water Esmer- alda formation in that its fauna denotes a i3robable marine origin. In this respect, also, it seems to be different from the rest of the known Tertiary strata, which extend in a more or less continuous belt from this district south into the Mohave Desert, and the present aspect of our knowledge indicates that it represents a period during which conditions were quite different from those which followed. PLIOCENE. On the western side of Excelsior Flat the lava is underlain by a solid but friable deposit, consisting of ash and pumice, having the appearance of being waterlaid. This occurs at an elevation of about 5,500 feet. In the valley below and to the east of this are less con- solidated, horizontally stratified gravels, containing pebbles of lava and reaching up nearly to the same elevation. On the eastern flanks of the Excelsior Mountains, overlooking Soda Springs Valley, there was noted, at an elevation of 5,250 feet, hori- zontally stratified gravels and volcanic tuffs, lying uuconformably against the folded Tertiary series and partially consolidated. The regular stratification of these deposits suggests that they are lake a Am. GeoL, Vol. XXV, 1900, p 168. See also this report, p 185. 112 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. sediments, aud they are probably to be correlated with similar sedi- ments found all over the region north and west of here, which have been called Pliocene. IGNEOUS ROCKS. Along the road between Hawthorne and Sodaville, which passes through Excelsior Flat, there is, on the west border of the hills, a belt of fine-grained lava, which forms broad, slightly dissected mesas. A specimen of this lava proved to be pja-oxene-olivine-basalt. It occu- pies a large area, inclosing the body of probable Tertiary limestone, whicli it overlies, and toward the east forms a considerable portion of the main ridge of tlie Excelsior Mountains, of the spurs which run north from it, and of the parallel east-west ridge with which these spurs connect. It overlies the probable Tertiary sandstones and shales and the stratified, water-laid tuffs and gravels of the Pliocene. South of the main range the earlier Tertiary series is again overlain by slightly dissected lava, and this lava runs southward into the Can- delaria Mountains, where a prominent peak has the aspect of a slightly denuded volcanic cone. The fact that this lava overlies all the stratified rocks, even the supposedly Pliocene gravels, together with its very slight erosion, shows that it is very young, probably early Pleistocene. The comi)o- sition of the lava bears out this reasoning, for it is probably to be correlated with the Pleistocene basalts described in other ranges.*^ GRANITIC ROCKS. As seen from Excelsior Flat, a considerable portion of the highest part of the Excelsior Mountains to the southwest consists of gray, rugged- weathering granitic rocks. At the abrujit eastern end of the main range the earlier Tertiary sandstone and shale series is contorted and apparently cut by granitic dikes. STRUCTURE. To the north of the main ridge, the general east-west valley, which is in part occupied by Excelsior Flat, seems to lie along the axis of an anticlinal fold with east-west strike. The main ridge lies on the southern limb of this fold, while the minor ridge lying north of the valley and parallel to the main one, is on the northern limb. Northwest of Excelsior Flat the area of probably Tertiary lime- stone first described^ forms one of the north-south spurs which run at right angles to the main range. The structure of this spur is anti- clinal, but the strike of the fold is north and south. «J. E. Spurr, Succession and relation of lavas in the Grreat Basin region: Jour. Geol., Vol. VIII, p. 636. b See p. 109. SPUBR] EXCELSIOE AND CANDELAKIA MOUNTAINS. 113 ORES. There lias been considerable mineralization in the Excelsior Moun- tains. On the west side, along the road traveled, there has been mineralization in the limestoue near the contact with the overlying lava. Farther east the red sandstones are found to be bleached and to contain disseminated copper minerals. On the eastern end of the main range are ore deposits, associated with crnmpling of the strata and probably with granitic dikes. RESUME. The rocks of the mountains are probably Early Tertiary limestones, together with a series of sandstones and shales with some conglomer- ates. The relative age of the limestones and sandstone shales is uncertain. These two series were folded together. While the main folds trended east and west, a minor set had north-south axes. At about the same time came the intrusion of granitic rocks as dikes and larger masses; the ore deposition was also probably nearly contem- poraneous. After this came deep and long-continued erosion, bring- ing about the present topography and followed by the formation of the Pliocene lake. Finally this lake receded and great sheets of basalt were poured out. CANDELARIA MOUNTAINS. The term Candelaria Mountains is here applied to an irregular group, reaching from the California-Nevada State line eastward to the Columbus Valley. It lies Just north of the White Mountain range and south of the Excelsior Mountains. SEDIMENTARY ROCKS. CAMBRIAN. Mr. F. B. Weeks, who visited the mountains in 1899, has informed the writer of the existence of a considerable thickness of quartzite and limestone (see PL I). No identifiable fossils were found. CARBONIFEROUS. On the road between Columbus and Candelaria there occnr dark- graj^ nearly black, quartzites, and stretched conglomerates, with some coarse sandstones and nearly white fine-grained chert. Mr. H. W. Turner has kindlj^ supplied the writer with the following note concerning the disco veiy of Carboniferous fossils in this rock: I am indebted to William Grozenger for information as to tliis locality, which lies 3 miles northwest of Columbus by the trail to Candelaria, at an elevation of about 4,900 feet. Similar fossils also occur in the gulch just north of this point at Bull. 208—03 8 114 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. an elevation of aboiit 5,300 feet. These fossils were referred to Mr. Charles Schu- chert, of the United States National Museum, who reports that the collection contains two Carbonic species, a Productus and a Spirifer. Both are specifically tindeterinined at present. The Spirifer (apparently a new species) belongs to the S. eavieratus section, fossils recognized as characteristic of the Upper Carbonic. The Productus is apparently identical with one from the region north of Mount Shasta, in California, also associated with Upper Carbonic species. These forms remind one more of the Carboniferous fauna found in the Shasta region than of the Carboniferous farther east. EARLIER TERTIARIES. Adjoining the Carboniferous rocks to the northeast, and probably overlying them is a comparatively small area of brown, yellow, some- times purplish, limy and sandy shales, argillaceous fine sandstones, and thin-bedded brown and yellow aphanitic limestones. This series strikes N. 65° E., and dips 65° NW. It is probably identical with the rocks of the Esmeralda formation a few miles to the south, In the southern end of the Monte Cristo Mountains. At one place the upturned edges of the stratified rocks are overlain by a thin sheet of siliceous rock, so glassy that the microscope does not show its true character, but it is probably rhyolite and susceptible of correlation with the rhyolite overlying the sedimentary rocks in the Monte Cristo Mountains. PLIOCENE BEDS. At the gap which separates the Pilot Mountains from the Cande- laria Mountains, just north of Candelaria, occur certain horizontally stratified clays and sands which have already been mentioned, in describing the Pilot Mountains, as belonging to the group of Pliocene sediments. IGNEOUS ROCKS. Overlying the Pliocene sediments not far north of Candelaria, thin sheets of olivine-basalt were found (Pleistocene). South of liere, over- lying the stratified beds of the Esmeralda formation, were found the sheets of glassy rhyolite above mentioned. West of Columbus and Candelaria, a large part of the range appears to be comj)osed of red and gray lavas overlying and often concealing the sedimentary rocks. As seen from Sodaville, the northern part of this mountain group is also chiefly volcanic, the topography showing such smooth, mesa-like forms, and so little erosion that the rocks were considered as probabl}^ belonging to the Pleistocene lavas. A prominent peak in the central portion of the Candelaria Mountains has the aspect of a little denuded volcanic cone." a These observations have been confirmed by Messrs. Turner and Weeks, who visited the range separately the same year as did the writer. Mr. Turner states that the bills north of Benton are also all lavas. SPURR.] RANGES OF WEST-CENTEAL NEVADA. 115 WALKER RIVER RANGE. The Walker River, or Wassiiek, Range is a straight, bold ridge of mountains, rising immediately from the west shore of Walker Lake. It has a trend a little west of north and a length of about (50 miles. It is separated on the north from the volcanic Desert Mountains by the Walker River Valley, and on the south it passes into the irregular Excelsior Mountains. Throughout most of its course the range is characterized by the comj)aratively gentle slope of the west side and a steep scarp on the east. IGNEOUS ROCKS. Almost all the rocks of the Walker River Range are igneous. Those on the steep eastern face are generally granular, and those on the west side typical volcanics. GRANULAR ROCKS. Just west of the Indian agency at the upper end of Walker Lake, the rock of the mountains is chiefly a coarse-grained biotite-granite. Farther north, near the point where the road crosses the range, biotite-granite-aplite, of a distinctly more siliceous variety than the first, occurs in conjunction with great masses of alaskite-aplifce. On the road which crosses the range, at a point southwest of Haw- thorne, the summit and greater part of the mountain range appears to be also of decomjiosed biotite-granite. Between these two locali- ties the granite is i^robably nearly or quite continuous. Underlying the biotite-granite, at the point first described, is a dark rock, specimens of which proved to be hornblende-quartz-syenite and biotite-hornblende-quartz-monzonite. The granite is shown by its branching dikes to be intrusive into the more basic rock. Both rocks are cut by dikes of alaskite, which grows very siliceous and runs out in places to nearly pure quartz. In the cream-colored mountain of granite and alaskite around which the road turns in crossing the range, the alaskite is evidently younger than the siliceous granite, into which, however, it x^asses by transitional stages as regards its composition. The granite some- times contains large feldspar phenocrysts, similar to those of the rock near Belmont and near Ellsworth. At the pass southwest from Hawthorne, the biotite-granite which occupies the summit of the mountains is succeeded farther east by metamorphosed igneous rocks, probably altered by dynamic move- ments. These rocks lie along the face of a bold, eastward-facing scarp. As examined microscopically, they consist of aposyenite-por- phyry, apogranite, and apoalaskite, with some biotite-rhyolite, which may be later than the others. These metamorphosed igneous rocks are confused with some highly altered limestones and quartzites. 116 GEOLOGY OF NEVADA SOUTH OF 40TH PAEALLEL. [bull.308. On the west side of the cream-colored mountain which lies north- west of the north end of Walker Lake, on the road across the range, the granular rocks, already described, pass under and into gray and red volcanics, which dip 30° to 45° SW. away from the mountain. About the point where the granular rock gives place to the evident volcanics, specimens were collected, which proved to be alaskite- IDorphjay and tordrillite, the latter with a finely cryptocrystalline groundmass. Overlying these siliceous rocks was found augite-biotite- aleutite. West of this point, near the summit of the range, the prev- alent rock is biotite-andesite, containing many angular fragments of a darker lava. The whole western side of the mountains is volcanic. IGNEOUS ROCKS SHOWING TRANSITIONS OF TEXTURE. In a small butte (Mason Butte) which emerges from the Pleisto- cene valley deposits to the west of the northern part of the Walker River Range, a few miles south of Wabuska, an intersecting series of igneous rocks was studied. The butte presents the appearance of a typical volcanic rock, being distinctl}^ and thinly bedded and of red and gray colors. Upon examination the rocks are found to be in part granular and in part fine grained and j)orphyritic, the different textures alternating in conformable beds. Examined microscopicallj', the coarse-grained rocks are hornblende-biotite-quartz-diorites, while the fine-grained ones are hornblende-biotite-quartz-andesites. The chemical composi- tion of the two rocks is also nearly the same. Sometimes the coarse- grained and the fine-grained types api^ear in the same bed, one apparently being formed at the same time as the other; generally, however, the beds are separate. The hyj)othesis adopted by the writer is that these rocks are the roots of old volcanic flows which have been exposed by the removal of the overlying portions of the lava through the erosion of Walker River, in whose valley the butte lies. The whole appears to have been an igneous mass in process of slow flowage, some streaks of which crystallized rapidly, with the texture of true lavas, while between them portions of the same magma crystallized more slowly, as granular rocks.'* Facts suggesting similar transitions of texture were noted within the main Walker River Range, but are not described on account of insufficient evidence. SEDIMENTARY ROCKS. PLEISTOCENE. Professor Russell lias described the history ^ and the sediments of the Pleistocene Lake Lahontan, an arm of which occupied the valley a For a fuller statement of this problem see J. E. Spiirr, Variations of texture of certain Terti- ary igneous rocks in the Great Basin: Jour. GeoL, Vol. IX, p. 586. 6 Men. U. S. Geol. Survey Vol. XI, SPURR] WALKER RIVER AND SMITH VALLEY RANGES. 117 of the present Walker Lake. The writer also observed these sedi- ments as well as older stratified deposits, which reach higher up in the mountains. The line between the Pleistocene and the Tertiary has not been closely di-awn in this region, and probablj^ a portion of those dej)Osits older than the Lahontan sediments are still Pleisto- cene, but at present the writer will include under that head only the deposits of the lake described b}^ Russell. In the valley of Walker Lake the dej)tli of the Pleistocene Lake Lahontan at its highest stage was 225 feet. At the upper end of the present Walker Lake the elevation is 4,120 feet above sea level, which would make the surface of Lake Lahontan at this iDoint 4,845 feet. At about this altitude, as measured by the barometer, the writer found a heavy terrace, and about 200 feet above this a still heavier one, the top of the main terrace being about 4,600 feet high. These terraces are constructional and show a rude horizontal stratification. They are composed largely of gravels and huge bowlders from the adjacent mountains. At another point, farther north, the altitude of this same chief terrace was determined as 4,675 feet. On tlie opposite side of the valley, on the slopes of the Painted Mesa (which forms part of the Desert Mountains), corresponding dej)osits may also be seen, taking the form of inclined slopes or ancient beaches rather than of sharpl}^ cut terraces. PRE-LAHONTAN SEDIMENTS. About 100 feet above the heaviest terrace just mentioned is a lesser constructional terrace, and about 400 feet higher there is on the mountains a rock-cut bench which is probably also a water line. This rock-cut bench is at an altitude of about 5,100 feet, or about 700 feet above the surface of the ancient Lake Lahontan, while the con- structional terrace below it is about 300 feet above the old surface. Crossing the southern end of the range, coarse, horizontally stratified material, consisting of little assorted volcanic rock, is found to the summit, where it forms hills 400 or 500 feet high, reaching up to an altitude of about 5,730 feet, or 1,385 feet above the surface of Lake Lahontan. On the western side of the range, at the point where the road crosses due southwest from Hawthorne, stratified gravels are found u]3 to a height of 7,100 feet. These deposits seem to be water-laid. They are evidently pre-Lahontan, and if formed in a lake occupied a body of Avater which was the ancestor of the Pleistocene lake, but of vastlj greater dimensions and probabl}^ of longer life. From reasons entailed in the correlation of these gravels with others throughout the region these deposits are provisionally classified as Pliocene. SMITH VALLEY RANGE. The name Smith Valley Range may be applied to a low and narrow moF ntain ridge, which on the north merges Avith the Pine Nut Range, 118 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. and on the south spreads out broadly into a series of volcanic mesas, which connect farther south with a spur of the Sierras north of Lake Mono. The range as thus defined separates Mason Valley, on the east, from Smith Valley, on the west. IGNEOUS ROCKS. Smith Valley Range is essentially volcanic. At the northern end, where it merges into the Pine Nut Range, specimens of the lava, form- ing comparatively^ well-dissected mountains, are found to consist of hypersthene and biotite-andesite, with some biotite-dacite. South- ward from here the range is evidently volcanic, but it was not examined closely except in the region of Dalzell Canyon, which separates the southern part of the range tro^n the Sweetwater Mountains, fai'ther west. In Dalzell Canyon the oldest formation consists of granite and rhyolite, and is altered and jointed. Overlying this is iJja^oxene- hornblende-andesite, and still higher are comparatively slightly eroded mesas of more siliceous andesitic rock, or hornblende-biotite-latite. On the road which cuts across the low southern end of the range east of Sweetwater, following the upper part of the East Walker 'River Valley, the siliceous andesite and latite flows are succeeded on the east by more basic thin-bedded andesitic or basaltic lava, largely glassy. This overlies sands, clays, and conglomerates, which will presently be described as probably Pliocene. It has flowed into and dammed up the valley eroded in the earlier lavas. It is therefore the latest of all and is i^robably Pleistocene. Farther east this same glassy lava occupies a considerable area in the bottom of the broad Walker River Valley, and forms broad mesas on the flanks of the Smith Valley Range on f he west and the Walker River Range on the east, and, reaching around to the south, forms a large part of the hills between the Walker River Vallej^ and Mono Valley. At the southern end of Walker River Valley, a few miles north of Auroi-a, is a little- defaced volcanic cone of red lava, which probajbly belongs to the same epoch. This has been called the Aurora Crater on the topographic map accompanying Professor Russell's paper on Lake Mono.^' These lavas everywhere overlie the stratified gravels which occur in the southern part of the Walker Lake Valley, in the same manner as already mentioned. South of here, in the basin of Lake Mono, Professor Russell* has described various lavas, including hypersthene- andesite verging upon basalt, and rhy9lite, which are evidently Pleistocene. These lavas belong to the same class as those just described, and seem to corre- spond with the thin flows capping the Pliocene gravels near Welling- ton on the Sweetwater Range, and also to the thin flow of basalt which a Eighth Ann. Rept. U. S. Geol. Survey, Pt. I, PI. XVII. 6 Ibid., pp. 374, 375, 377, 380. SPURR] SMITH VALLEY RANGE. 119 constitutes the latest volcanic rock in Eldorado Canj^on in the Pine Nut Range;** hut in the district under immediate consideration we have a vastly greater amount of Pleistocene volcanic action than was ohserved anywhere else in the region. SEDIMENTARY ROCKS. Just south of Dalzell Canyon were found well-stratified arkoses and little- worn conglomerates, containing chiefly angulai- fragments. These seem to cover the whole of a broad upland valley, to its abrupt end at the base of the Sweetwater Mountains, at an elevation of some- thing over 7,000 feet. As one goes southeastward from here, i^assing Sweetwater post- office and proceeding down the valley of Walker River where this cuts across the range, one finds, at an elevation of 6,500 feet at least, and below, well-stratified, washed, and assorted, hori- zontally or slightly cross-bedded sandstones, arkoses, and gravels. These rocks are often firmly consolidated, though friable, and resem- ble the sandstones near Carson, as exposed at the State prison.* The pebbles in the gravels are evidently derived from tlie andesite which is the main rock of the Smith Vallej^^ Range. Farther west, on the slopes of the hills facing the main Walker River Vallej*, a section of these deposits 100 feet thick was examined. Near the bottom were found sandy clays, which may be in part water-laid volcanic ash. Farther up come hard gravels, the well-rolled pebbles comi)rising various varieties of hornblende- and mica-andesite. Above this comes a compact gray sandstone, also made ux3 of volcanic debris and contain- ing fragments of white decomposed pumice. Capping the sedimen- tary rocks and overlying them, with a considerable angle of divergence, comes a thin sheet of andesitic or basaltic lava with glassy base. The top of this section has an altitude of about 0,150 feet. A short dis- tance away from this section the highest sandstone reaches an altitude of about 6,350 feet and is exposed as a simple bench in the mountains, the overlying lava having been eroded back from it. Along the north- ern slopes of the mountains which form the southern end of the Walker River Valley, northwest from Aurora, are continuous benches, the best marked of which can be little less than 7,000 feet in height. Below this are other sharp smooth benches of horizontal sandstone. The comparatively recent volcanic cone above referred to, lying north- east from Aurora, is benched up to 6,700 or 6,800 feet, but not higher. These terraces appear to grow somewhat higher to the south. The whole valley here is covered with the sandstones above described, which have been considerably eroded. At least 700 or 800 feet of this sedimentarj^ series is exposed. On the road which crosses the southern end of the East Walker River Valley and goes over the Walker River Range to Hawthorne, a See pp. 121 and 126. b See p. 124. 120 GEOLOGY OF TSTEVADA SOUTH OF 40TH PARALLEL, [bull.208. horizontally stratified gravels, apparently belonging to the same series as the sandstones above mentioned, occnr, frequently overlain b}'' glassy and slaggy andesitie or basaltic lavas, up to a height of 7,100 feet, where they give way to a fresh lava, above which all is decom- posed granite. All these comparatively recent horizontal sediments are provision- ally^ classed as Pliocene. PINE NUT RANGE. TOPOGRAPHY. The Pine Nut Range lies immediately east of the Sierra Nevada, and has much of the bold irregular topograph}^ of that range. As contrasted with the mountains of the more arid regions farther east, it* is distinguished by deeper dissection, affording more profound canyons and more abrupt cliffs. The eastern face of the range is steep, the western side in general less abrupt. Wherever this range was visited, numerous springs were observed, and the dissection seemed to be largely the result of water derived from these sources. The springs seem to be arranged, in part at least, along north-south lines, which are probably lines of fracture. These lines are deeper than the regions between, Avhich stand up as ridges; but whether these ridges are directly due to displacement, or have been left as such by the erosion of depressions along the lines of spring water, is uncertain. On the western side, between Daj^ton and Carson, the peculiarlj' wild and rugged topograi:)hy is caused bj^ the Carson River and its mountain tributaries which, in late Tertiarj^ or Pleistocene time, have dissected the mountain and the adjacent plateau-valle3^ IGNEOUS ROCKS. Nearly the whole mass of the range is igneous. The rocks Avere studied principally along two sections, one across the range southeast from Dayton and the other on the road between Wellington and Genoa. In the eastern part of the first-mentioned section, in the loAver mountains which here lie to the east of the main range and are con- nected with the northern end of the Smith Vallej^ Range, chiefly andesitie rocks were found. The andesite contains different ferro- magnesian minerals, including hornblende, augite, hypersthene, bronzite, and biotite. Occasionally biotite-dacite or quartz-andesite is found. Where erosion has cut deeply into the lava, coarser, denser, more massive, and more porjjhyritic forms are exposed. At the bot- tom of one of these canyons the lava is a fine-grained diorite-porphyry, while farther up it is hypersthene-bronzite-andesite with some dacite. Farther west, on the eastern scarp of the main range, occur gran- SPURR] PINE NUT EANGE. 121 iilar I'ocks. These, when examined microscopically, tnrned ont. to be hornblende-biotite-granite, sometimes porphyritic, and alaskite. The same granular siliceous rocks are exposed nearly to the summit, and they occur also on the western side of the divide. Here they are overlain by hornblende-, augite-, and hypersthene-andesites. About halfway down the mountains, in Eldorado Canyon, where the road leading to Dayton runs, there are hills of gently folded grav- els and coarse clays, the gravels being derived almost entirely from the andesites. They are exposed best in the arroyos, where they are overlain unconformablj^ hy 8 or 10 feet" of stratified bowlders and soil, which represent the recent stream accumulations. Farther doAvn the canyon is a volcanic breccia with rounded andesite bowlders, prob- ablj^ water-laid. This breccia is followed by thin flows of slaggy white lava, which contains numerous included angular fragments of andes- ite; these flows are interbedded with ash. The present canyon has been worn down through this breccia, ash, and porous white lava deposit. In several places a thin sheet of basalt has been poured ont after the development of the present topography (fig. 8). This sheet Fig. 8.— Section of Eldorado Canyon, Pine Nut Range. 1. Stratified rhyolite ash. 2. Basalt. also occupies the tops of some of the neighboring hillocks, which have been separated from one another by erosion subsequent to the last volcanic outbursts. In the canyon of the Carson River, a few miles southwest of Dayton, the stream has cut down 400 to 800 feet, exposing lavas like those in Eldorado Canj^on. The uppermost of these flows is a Avliite, little- compacted rhj^olite, while beneath it are large masses of a rock recog- nized in the field as lava, which on microscopic examination appears to be monzonite-porphjay. This is perhaps a coarser variation of andesite. Between Dayton and Wellington the Pine Nut Range is mainly igneous. The central ridge has a massive aspect in general, and is probably made up of the granitic rocks. Where the road between Genoa and Wellington crosses the range, hornblende-biotite-andesites occur on the western slopes. As in Eldorado Canyon, the whole system of gulches has been cut in this lava. 122 GEOLOGY OF NEVADA SOUTH OP 40TH PAEALLEL. [bull.208. Near the summit of the low pass on this road were found cliffs of a dense, massive, volcanic breccia with horizontal bedding and con- taining pebbles of rhyolite only. Some distance farther up, appar- ently belonging to the same series as the breccia, was found an ancient, apparently water-laid tuff, which microscopic examination shows to be rhyolitic, with above it a bed of coarse volcanic grit, and still higher a bed of volcanic conglomerate with large well-rounded pebbles of biotite-rhyolite and a matrix derived from the same rock. A short distance farther the rocks from which these detritals are derived were found in place in a hill to the north of the valley and to the east of the pass. This rock shows many and great variations, passing from a fine-grained aphanitic rhyolite to coarse granite and alaskite, and these variations are .arranged in thin bands. These are essentially quartz-feldspar rocks, generall}" containing biotite. They comprise biotite-rhyolite, fine-grained granite-porphyry, medium-grained biotite-granite, coarse-grained alaskite and granite- aplite, and one sjpecimen was a fine-grained quartz-monzonite-porphyry. These different varieties present, textn rally and structurally, almost perfect transitions from one to another, ranging from coarse granites through the granite-aplites and porphyries to the rhyolite, and the development of the different structures from the fine-grained rhj^olite is very clear and instructive. Only one band was found which did not belong to the general granitic series. This was a band of dark- green slaty rock, which, when examined, proved to be probably horn- blende-andesite; j^et this rock does not appear to be intrusive, but to form a band or streak probably contemporaneous with the more siliceous rocks. West of this old granite-rhyoiite area, andesite comes in above it again, of the same kind as before. Where it has been deeplj^ eroded a coarser- textural type is exposed; for example, the hornblende- andesite with cryptocrystalline groundmass, which represents the rocks near the surface, gives way in some deeper cuts to hornblende- andesite with granular groundmass, which is transitional to horn- blende-diorite-porphyry, SEDIMENTARY ROCKS. TRIASSIC LIMESTONE. Southeast of Dayton, limestone, in extremely scanty outcrops, just visible beneath the overlying volcanics, was found on both sides of the range. On the eastern side the limestone is massive, dark-blue and sometimes siliceous. Its laminae are vertical, although they may result more from shearing than from stratification. It is cut by andesite dikes. On the western side of the mountain, in Eldorado Canyon, the limestone is also blue and siliceous, changing to shaly and carbonaceous. It is crushed and seamed, but ajDpears nearly SPURR.l PINE KUT RANGE. 123 horizontal. The shal}^ limestone contains nearly obliterated fossils, npon which Mr. T. W. Stanton comments as follows: The collection * * * yielded only fragments and impressions of a Pecten and a specimen that appears to be part of an Ammonite. These are Mesozoic and probably Triassic. This locality is probably the same as that mentioned by Whitney'* as having- yielded the Triassic fossil Goniatites Icevidorsatus Ilauer. This Triassic limestone is probablj^ to be correlated with King's Triassic Star Peak limestone.* In the Pine Nut Range the limestone is probably older than the granitic rock which forms the main range, between its two outcrops. Scale 10 feet Fig. 9.— Sketch section of wall of arroyo in bottom of Eldorado Canyon, Pine Nut Range. 1. Gravels (pebbles mostly andesite) with coarse clays (Plio- cene— Shoshone lake sediments?) . Tilting probably local. 2. stratified bowlders and earth (Pleistocene). for it contains no granitic detritus. The granite must have burst up through the limestone in a great belt. PLIOCENE DEPOSITS. On the west flanks of the mountains above Dayton, as already described, there are found some hardened, well-stratified gravels and clays, derived from the andesites, and overlain, often unconform- ably, by stream gravels (fig. 9). They have the appearance of having been deposited in moving water, but this aspect may well have resulted from current action in a stable water-bod5^ On the face of the range just east of Daj- ton there is a rough inclined plane running uj^ to a height of 6,000 feet and terminating in obscure benches. Above this termination the mountain rises sharply and steeply, as vnsij be seen on the Carson topographic sheet j)ublished by the U. S. Geological aGeol. Sm-v. California; Vol. I, p. 459. bU. S. Geol. Expl. Fortieth Par., Vol. I, p. 270. 124 GEOLOGY OF NEVADA. SOUTH OF 40TH PAEALLEL. [bull. 208. Survey. The approximately horizontal upper limit of the plane sug- gests lake action, and the older gravels and clays in Eldorado Canyon strengthen the idea. At Dayton Professor Russell'' has placed the limit of one of the bays of Lake Lahontan at an elevation of 4,375 feet. The above-mentioned bench is, therefore, 1,625 feet above the uppermost limit of the Pleistocene lake. Southward from Dayton the leveled plane was not observed, and it is probable that some of the lavas which here form the mountain flanks were laid down in the lake period and so covered the ]3lane or prevented its erosion. In the plateau valley between Dayton and Carson there occur stratified clays and coarse gravels, at heights of several hundred feet above the Pleistocene Lake Lahontan. Near Carson there occurs a hardened sandstone or granitic arkose, which is well exposed at the State prison. The rock here contains plant remains and occasional fresh-water shells. One of these shells submitted to Dr. W. H. Dall was determined as Anodonfa, belonging to a recent species found living in California. Dr. Dall adds that the species may be older than the Pleistocene, since the genus goes back as far as the Eocene; but that since the genus is so easily affected by environment, the same species is rarely found in more than two horizons. Excavations in this rock at the State prison have brought to light layers covered with footprints of the extinct elephant and other mammals and birds. On the hill south from the prison there is benching up to a height of 4,850 feet. The same sandstone as shown at the State j)rison, but some- what looser and more friable, occurs west of Carson at the foot of the Sierras.^ South of this point, along the face of the range, there is a belt of low hills often covered \\\) bj^ the Pleistocene detritus, but consisting, when exposed, of stratified sands and gravels. On the western face of the Pine Nut Range, southward from Carson, there is generallj'^ visible a distinct line in the topograi)hy at about 6,000 feet, below which the slopes are gentler and above which the mountains are steeper and more rugged. Along the road which crosses the range from Genoa to Wellington stratified sands and gravels, carrying well- rounded pebbles, occur in hills covering the gentlj^ inclined plain at aMon. U. S. Geol. Survey, Vol. XI, PL XLVI. ft After writing the above description the writer found that the locality had been already better described by Professor Le Conte and others. He lets his own description stand only to show how independent observations have led to similar conclusions. Professor Le Conte (On certain remarkable tracks, found in therocksof Carson quarry: Proc. Cal. Acad. Sci., Aug. 27, 1882) describes a few fresh- water fossil shells of species still living in the vicinity. Among the vertebrate remains are fragments of tusks and molars of an elephant, and molars and fragments of jaws containing molars of two species of horse. Concerning the age of the beds he conclvides that if not Quaternary, they can not be earlier than Upper Pliocene passing into Quaternary. He also suggests that they are possibly deposits of King's Lake Shoshone, and not Lake Lahontan. Professor Le Conte observed that the level at this locality is 240 feet higher than the upper- most shore line of the Pleistocene Lake Lahontan, which, moreover, did not extend so far west as Carson. SPURR.J PINE NUT AND SWEETWATER RANGES. 125 the base of the steeper mountains. These hills are considerably eroded. Near the mountains the jjebbles are larger, and in crossing the range the stratified deposit stops at 6,000 feet precisely, above which the rocks are bare. Below the uj)permost gravels are benches in the detritus and in the lava on which the detritus lies. These benches, as well as the canyon of the Carson River at this point, seem to have been cut during the recession of the lake to which the gravels owe their origin, and whose uppermost shore line was at the G, 000-foot cut. On the western side of the range there is also a pronounced scarp above the 6,000-foot contour, and beneath this stratified gravels constitute the foundation of the valley between the Pine Nut Range and the northern end of the Sweetwater Range. The uniform and general distribution of these water-deposited gravels and sands, up to about 6,000 feet, and the horizontal groin which occurs on the mountains about the same height, suggest that the deposits were laid down in a lake, which had its surface at its time of maximum extension at the altitude above mentioned. That the lake was older than the Pleistocene is shown b}^ the fact that the Pleisto- cene Lake Lahontan reached an altitude of only 4,375 feet. The indu- ration of the sediments of this higher lake, as seen in the sandstone of Carson, also i)oints to a greater age; and the great amount of sub- sequent erosion, illustrated in the carving of the canyon of Carson River, indicates that the maximum extent of the lake was at a period which was removed from the period of maximum extension of Lake Lahontan by a time interval much longer than from the latter x^eriod to the present day. On the whole the deposits of this older lake will be considered late Pliocene. SWEET\A^ATER RANGE. The Sweetwater Range may be considered as the southern prolonga- tion of the Pine Nut Range, from Avhich it is separated by the valley of the West Walker River, at Wellington. It is also a spur of the Sierras, into which it passes at its southern end, TOPOGRAPHY. The Sweetwater Mountains are high and rugged for the most part, with bold peaks and cliffs. The eastern face of the northern part of the range, from Wellington southward to Desert Creek, is steep and straight. Southwest of Wellington the West Walker River has cut a deep canyon along the face of the range, below the level of the broad desert valley separating it from the Pine Nut Range. On the road from Wellington to Sweetwater, the Sweetwater Range is separated from the Smith Valley Range on the east by the deeply cut Dalzell Canyon. 126 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. IGNEOUS ROCKS. POST-PLIOCENE BASALTIC LAVA. The gravels and sands which occur in the valley separating the northern end of the Sweetwater Range from the Pine Nut Range belong to the ancient sediments which have already been provisionally classified as Pliocene. Along the canyon of the West Walker River, a short distance southwest of Wellington, there occur in places sheets of columnar basaltic lava, overlying the gravels. This is probably nearl}^ contemporaneous with the basalt in Eldorado Canyon, of the Pine Nut Range. LATE RHYOLITIC LAVA. The highest i)ortion of the Sweetwater Range, just west of the post- office at SweetAvater, is distinguished by the brilliant light-gray, yellow, and red which its rocks assume on Aveathering. These rocks all seem to be gray, essentially fine-grained, thin-bedded surface volcanics. They Avere not examined in place, but a typical specimen selected from the blocks derived from this mountain proves on chemical analysis to be A^ery siliceous rhyolite'^' or tordrillite.* LATE ANDESITE AND LATITE. In the same canyon as above mentioned (near Wellington), there occurs, beneath the rolled gravels, stratified ash, dipping nortliAA^est aAvay from the mountains. Below this ash occurs lava, through which also the river has cut. There are two distinct flows, the lower of Avhich has a perfect columnar jointing, Avhile the upper one is often brecciated and rests uj)on the apparently eroded surface of the lower. The rock of the loAA^er flow, microscopically examined, proves to be bronzite-andesite, that of the upper one hornblende-biotite-latite. The uppermost of these floAvs has been deepl}^ weathered, and has been displaced by a fault, which is subsequent to the weathering. The andesite is of the same composition as the ancient andesite AA'hich forms the greater part of the range, but its association Avith breccias and graA^els stamp it as being younger than the main mass and intermediate belAveen it and the latite. In Dalzell Canyon are coarse volcanic breccias, Avith thin inter- banded flows, all dipping at moderate angles irregularl3^ A specimen from a hard bowlder in the breccia is hornblende-bronzite-andesite. These breccias and thin flows are probably younger than the massive andesite of the main range. They are very likely of about the same a Dr. H. W. Fairbanks (Am. Geol., Vol. XVII, p. 152) mentions a rock in Ferris Canyon, in the Sweetwater Range, which is probably the same as that above described. f> TordriUite is proposed as the flne-grained equivalent of alaskite, and differs from rhyolite in being in general more siliceous and containing no essential feiTomagnesian minerals. See J. E. Spurr, Classification of igneous rocks according to composition: Am. Geol., Vol. XXV, 1900, p. 210. SPURR] SWEET WATEE EANGE. 127 age as the breccias in Eldorado Canyon, in the Pine Nut Range, which they resemble exactly. Jnst south of the post-office at Sweetwater similar hornblende- bronzite-audesite comes in, overlying the ancient rhyolite series. This is of the same general age as the breccias in Dalzell Canyon. EARLIER ANDESITES. Most of the Sweetwater Range to the north of the high gray.rhyo- litic peaks above described is of red, deejjly eroded lava. Near Well- ington, and at the northern end of Desert Creek, specimens of this lava proved on examination to be hornblende-bronzite-andesite. The main mass of hornblende-pja'oxene-andesite forming the bulk of the Sweetwater Range is older than the thin flows and breccias previously described. The later andesites are closely associated with gravels which were chiefly derived from the erosion of the earlier andesite. EARLIER RHYOLITE. Just below Sweetwater there outcrops a gray lava which has some- what the aspect of a pj^roclastic breccia. A specimen proves to be rhyolite, with a microcrystalline granular groundmass, and contain- ing small fragments of a gray basic lava free from quartz. This rock is of exactly the same type as one examined from the banded granite- rhyolite series in the Pine Nut Range, on the road between Genoa and Wellington. At Sweetwater, also, this lava has an ancient appearance. It has a pronounced jointing, or sheeting, in two direc- tions, at right angles to one another, one striking N. 70° E. and dip- ping 70° SE., and the other dipping 70° NE. This rhyolite is over- lain by hornblende-bronzite-andesite. GRANITIC ROCKS. Along the eastern side of the northern portion af the Sweetwater Range, south of Wellington, there is, back of the main scarp, a second scarp composed of gray and massive rocks. In the bottom of the vallej' east of here are rolled pebbles and bowlders of granular and porphyritic granitic rocks. As one goes southward from here he may trace the scarp of gray rocks into Desert Creek Canyon, which seems to be cut in similar rocks, and the uppermost portion of Desert Creek Peak is seen to be of the same material. Just east of Desert Creek Peak, at Wileys, granite actually outcrops, beneath hornblende- bronzite-andesite. The granite is in part coarse and porphyritic, containing large feldspars, which have inclusions of dark minerals, and is of the same variety as noted at Belmont, Ellsworth, and on the eastern face of the Pine Nut Range, southeast from Dayton. There is also some nonporphyritic granite, and some containing few dark minerals, and so verging oh alaskite. 128 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. The granitic rocks have been decomposed to a depth of many feet, so that no specimens could be collected. This decomposition occurred before the eruption of the andesite, for this lava is fresh where it overlies the rotten granite. The period sufficient for this decomposi- tion is considerable, and it must have been preceded by a long period of erosion, which exposed the granite. In the valley drift above noted there was found, besides granite, specimens of porphyritic siliceous rock, transitional between granite and rhyolite. It is possible that the granite and the rhyolite at Sweetwater may be of nearly the same age and may be correlated with the ancient granite-rhyolite series of the Pine Nut Range. SEDIMENTARY ROCKS. PLIOCENE DEPOSITS. The valley which separates the northern end of the Sweetwater Range from the adjacent Pine Nut Range is covered with bedded gravels, through which West Walker River has cut a Pleistocene canyon. Besides the rolled gravels, which are largely derived from the andesite of the mountains, there are some beds of stratified ash. Across the range from here, the foot of the main scarp north of Desert Creek ends in a sloping lAahi at an elevation of 6,000 feet; and in the valley below this the deposits consist of rolled gravels similar to those exposed in Walker River Canyon. South of Dalzell Canyon and east of the highest peaks of the Sweet- water Range is a broad, gently sloping valley, several miles across, . reaching back to the Sweetwater Mountains, which rise sharply from i it at an altitude of about 7,000 feet. The surface of this valley is; smooth, and slight cuts in it show a stratified deposit of arkose and I angiilar fragments of lava.*^^ All these deposits are provisionally referred to the Pliocene. RESUME. Probably the oldest rocks of the range are a series of granites andi ancient rhyolites, which were perhaps contemporaneous. They have been jointed by dynamic action, and are deeply decomposed. The succeeding geologic formation was a hornblende-pyroxene- andesite, which was poured out in great masses over the underlying siliceous mountain core. Subsequent to this, the andesite was deeply eroded, and probably a lake was formed. The material-derived from the erosion of the andesite and of the underlying siliceous rock was spread out in the valleys as gravels. During this erosion period thin sheets of andesite similar to the main mass were poured out. a See description of Smith Valley Range, p. 119, SPURR.] SWEKTWATEK AND VIRGINIA RANGES. 129 Later than this, but also i^robably while the lak'^ still existed, a more siliceous lava, which has been classified as hornblende-latite, was poured out in comparatively thin sheets. The rhyolites or tor- drillites of the highest portion of the range were probably j)Oured out at approximately the same period, so far as we can judge from the amount of erosion. The shrinking of the lake exposed to erosion those lavas which had been poured out in it, and the present stream canyons were cut in the lake sediments and the lavas. At the same time thin sheets of basaltic lava were locally erupted. At the southern end of the Sweetwater Range there appears to have occurred, subsequent to the retreat of the lake, a local ui3lift, which has elevated the lake sediments and shore lines 1,000 feet above the same sediments in the regions north of here. VIRGINIA RANGE. The Virginia Range lies next east of the Sierras and north of Car- son. It is ceparated on the south from the Pine Nut Range by a narrow plateau valle}', in which Carson River has cut a Pleistocene canyon. The range rises abruptly from the plains at its base, and is high and rugged. The northern portion was examined by the geologists of the Fortieth Parallel Survey, and the geology of this part is represented on map 5 of the atlas accompanying that rei3ort. In the southern part of the range is the famous Comstock lode, and in this vicinity the geology has been studied in detail by King, Becker, and others. IGNEOUS ROCKS. With one or two nn important exceptions, the Virginia Range is made up entirely of igneous rocks. These were thoroughly studied by Dr. Becker," and later were made the subjectiof a critical study by Messrs. Hague and Iddings.^ The igneous rocks consist partly of rocks with porphyritic structure and fine-grained or glassy groundmass, partlj^ of those porphj^-itic rocks whose groundmass is comparativel}^ coarse, and x)artly of typical granular rocks. At first these rocks of different structures but simi- lar composition were described as distinct from one another and of different ages, but Hague and Iddings considered that the structures above enumerated occur in the same eruptive bodies, the finer-grained structures having occurred at or near the surface, while the coarsely granular ones are typical of the core of the mountain, now made accessible by the deep uiine workings. These conclusions Avere after- wards contested by Dr. Becker. a Geology of the Comstock lode and the Washoe district: Mon. U. S. Geol. Survey Vol. III. Also California Acad. Sci., Bull. 0, 1886. bOn the development of crystallization in the igneous rocks of Washoe, Nevada: Bull. U. S Geol. Survey No. 17. Bull. 208—03 9 130 GEOLOGY OF NEVADA rfOUTH OF 40TH PARALLEL, [bull. 208. According to Dr. Becker, the succession of igneous rocks in this district is, beginning with the oldest: Granite, metamoi^phics, granular diorites, porphyritic diorites, quartz-porphyry, porphyritic diabase, later diabase (black dike), earlier hornblende-andesite, augite-andesite, later hornblende-ande- site, basalt. The succession, according to Hague and Iddings, is as follows: 1. Pyroxene-hornblende-andesite (in its coarser inner portions becoming pyroxene-hornblende-diorite-porphyry and pyroxene-hornblende-dio- rite). Period of volcanic rest and denudation. 2. Hornblende-mica-andesite. 3. Dacite. 4. Rhyolite. 5. Pyroxene-andesite. 6. Basalt. All these igneous rocks are considered by Hague and Iddings as Tertiarj^, but they have been divided into Tertiary and pre-Tertiary by Becker and others. SEDIMENTARY ROCKS. ANCIENT LIMESTONES. Mr. Becker « described near Virginia a small area of distinctl}^ stratified rocks, consisting of limestones and greatly metamorphosed micaceous schists. No fossils Avere found. They are perhaps similar to the Triassic limestones found a few miles south of here, in the Pine Nut Range near Daj^oii. (See p. 207.) aMon. U. S. Geol. Survey Vol. Ill, p. 190. CHAPTER III. RANGES OF S0UTHER:N^ NEVABA. VIRGIN RANGE. The Virgin Range is just ^vithiu the eastern limit of the folded strata of the Basin ranges and west of the nearlj^ horizontal rocks of the Colorado Plateau.** According to Button,* the exact boundary between these two provinces is the Grand Wash, the vallej^ which lies immediately east of the Virgin Range. In this valley is a heavy fault with downthrow to the west. Dutton sa^^s : This fault is the boiindary of the G-rand Canyon district and of the Plateau country itself. The region beyond is a Sierra coimtry, with the same character- Lstics as the Great Basin of Nevada and western Utah. SEDIMENTARY ROCKS. PRE-TERTIARY. According to Marvine ^ the rocks exposed in the main body of the Virgin Range present the same general sequence as is shown in that portion of the range cut by the Colorado River. The fundamental rocks are Archean gneisses, schists, granites, etc., overlain by Cam- brian rocks, which in turn are capped by a great thickness of Carbon- ferous rocks of the Red Wall and Aubrey groups. At the extreme northern end of the range, east of Beaver Dam Wash, an area of red andstones, supposed to be Triassic, although no fossils were found, tias been maj)ped bj^ the geologists of the Wheeler Survey,^ but is not included in the map accompanying the present reiDort. PLIOCENE. Besides the Archean and Paleozoic rocks, Marvine * describes in the Jrand Wash, which lies just east of the Virgin Range, a series of ompact conglomerates, which constitute a very large amount of the t^alley filling and which have often been eroded into a rolling or hilly lUrface with deep valleys. This conglomerate contains some beds of ava, is horizontally bedded, and abuts unconformably against the 'olded Carboniferous rocks of the mountains. Southward from the aE. E. Howell, U. S. Geog. Surv. W. One Hundredtli Mer., Vol. Ill, p. 232. & C. E. Dutton, Second Ann. Rept. U. S. Geol. Survey, p. 126. cU. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 194. didem. Atlas, geologic sheet No. 66. e Idem, Vol. in, pp. 197, 198. 131 132 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. Colorado, in another valley, the same gravels or conglomerates are met with, overlain by calcareous tufas several hundred feet in thickness. On traveling along the west side of the Mormon Range toward the pass between it and the Muddy Range, the writer noted that the greater portion of the valley of the Virgin River lying east of the Virgin Range was covered with slightly eroded Tertiary strata, probably identical with the horizontal red, gray, and brown sand- stones and conglomerates observed in the lower portion of the Meadow Valley Wash/' The conglomerates in the Grand Wash, on the other side of the Virgin Range, described by Marvine, probably belong to the same series. As observed by the writer in the Meadow Valley Wash, they have the appearance of having been deposited in a lake, although it is possible that they represent the valley accumulation of the Colorado River, at a period when the streams of this system occu- pied wide valleys, in which they worked laterall}^ and deposited the material which they derived from the erosion of the mountains, the carrying power of the streams at that time not being equal to the amount of load received. These sediments occupy the older val- leys which were eroded in the Paleozoic limestones and in the earlier Tertiary sediments and lavas, but they were laid down before the down cutting of the latest sharp gorges, for they stand as the walls of these. They lie against the Carboniferous limestones, and, as described by Marvine, against the Archean granites along the Grand Wash. According to Dutton ^ the greater part of the general denudation of the Colorado drainage region was probably accomplished in Miocene time, whereas the cutting of the Grand Canyon probably began in the early part of the Pliocene. The conglomerates and sandstones under consideration were evidently deposited just before the period of rapid canyon cutting, and this, in conjunction with the evidence afforded by the underlying unconformable Tertiary rocks in Meadow Valley Canyon, may be sufficient grounds for specifying their age provision- ally as Pliocene. IGNEOUS ROCKS. Marvine^ describes large masses of black basaltic lavas resting upon the eastern base of the Virgin Range. Where the Colorado River cuts the range, at Virgin Canyon, Mr. Gilbert '^ describes lavas overlying the gneissic Archean rocks. STRUCTURE. As seen from the west, the limestones of the central portion of the Virgin Range present dips of 15° to 30°, and strikes indicating some- a See p. 143. '' Second Ann. Rept. U. S. Geol. Survey, p. 67. t-U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 196. dibid., p. 35. SPiTRR] VIEGIN EANGE AND COLORADO CANYON. 133 what irregular folding. Marvine " records that the main fold of the range is anticlinal and that a fault exists along the east face. This is j)robably the fanlt mentioned by Dntton,* which has a downthrow to the west of between 6,000 and 7,000 feet. Toward the south the folding appears to die ont so as to be nearly horizontal in the Colorado Canyon. COLORADO CANYON. That part of the canyon of the Colorado which is represented in the sontheastern corner of the map accompanying this report lies near the boundary between the Colorado Plateau on the east and the region of the Desert or Basin ranges on the west. The Colorado Plateau is characterized by nearly horizontal rocks forming mesas or benched platforms, while the region to the west has many different ranges of higii rugged mountains composed of folded strata. The rocks exposed in this portion of the canyon are Carboniferous and lower. At the mouth of the Grand Canyon Mr. Gilbert made a section showing^ over 5,600 feet of rocks, being all horizontal strata except the extreme base, where the granites and gneisses of the Archean appear. Above the Archean rocks are 755 feet of shales, sandstones, and some limestone belonging to the Upper Cambrian of the Tonto group. Above the Cambrian comes in, in aptparent con- formitj^, heavy limestones with some sandstones, having a thickness of 2,675 feet. This is the Red Wall limestone of the Carboniferous. Above the Red Wall comes in the Aubrey group of the Upper Car- boniferous, consisting of 1,300 feet of shales, sandstones, and cherty limestones. Later, Mr. Walcotf^^ found in the Grand Canyon a slight thick- ness of Devonian, rarely over 100 feet, between the Red Wall lime- stone and the Tonto rocks. Often the Devonian in this region is entirely absent, either through erosion or nondeposition. The rocks of this period are thin, purplish, fine-grained sandstones, becom- ing calcareous and containing unmistakable fossils. Mr. Walcott observed an erosion break at the top of the Tonto strata, and another between the Carboniferous and the Devonian. No Silurian rocks are present. At the base of the Tonto there is a great unconformity, beneath which occur sandstones, shales, limestones, and ancient lavas of the Chuar and Unkar divisions of the Grand Canyon group resting upon thin-bedded quartzites, which stand vertical and are broken through bj^ intrusive masses of granite. Mr. Walcott considers that the strata «U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, pp 194, 196. b Second Ann. Rept.U. S.Geol. Survey, p. 126; also Mon. U. S. Geol. Survey Vol. II, atlas PL II. <^U S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, fig. 82, p. 196. dAm. Jom-. Sci., 3d series, Vol. XXVI, pp. 437, 484. 134 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. between the Tonto and the thin -bedded qnartzites belong to the Algon- kian. The qnartzites are Algonkian or Archean." As one proceeds down the Colorado River from the Grand Canyon, he finds the upper strata successively disappearing, until, in Boulder Canyon and below, the Archean granites, gneisses, and schists come to the top of the canyon, except where covered up by Tertiary lavas. MORMON RANGE. The Mormon Range lies immediately east of Meadow YalleJ^ It has an extent of about 40 miles, and a north-northeast trend. At its south end it is divided from the Muddy Range by the valley of Muddy Creek, while at its northern end it merges into irregular volcanic mountains which cover a large area southeast of Pioche. In topography the Mormon Range is not extraordinarj^, its peaks being fairly rugged and of moderate height. Running along the central part of the range, and parallel with its axis, is a continuous notch or incipient valley, about 2,000 or 3,000 feet deep, which never- theless has not yet been deeply enough eroded to form part of the true valley system. SEDIMENTARY ROCKS. CARBONIFEROUS. The great bulk of the Mormon Range is almost free from igneous rocks and is made up of a dark-blue, sometimes crystalline limestone, with some reddish shaly beds. In Meadow Valley Canyon, on the northeast flanks of the range, a spur of this limestone contained the following fossils which were determined by Dr. Girty, of the United States Geological Survey, to be Upper Carboniferous: Crinoid steins. Productns punctatus?. Fenestellid. Spirifer cameratus. Fistulipora sp. . Spiriferina gonionotus. Productns nebraskensis. Seminula mira. Prodnctns splendens?. This is probably the Red Wall limestone group of Gilbert's Grand Canyon section.^ The same limestone series is exposed in Hackberry Canyon, a few miles south of here, and it probablj' constitutes the bulk of the range. In drift from the southern part of the range, found in the southern part of Meadow Vallej^ were pebbles containing the following Upper Cai'bouiferous fossils: Syringopora multattennata. Chsetetes milleporaceus? Fnsnlina cylindrica. Prodnctns semireticulatns. Archseocidaris sp. Below Hackberry Canj^on, in Meadow Valley Canyon, there is « Fourteenth Ann. Rept. U. S. Geol. Survey, pp. 505, 506, and 507. b U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, pp. 178, 196. SPURB.] MORMON RANGE. 135 found, overlying the more massive dark-blue limestone, a series of pink sandstones, clierty limestones, and shales of considerable thick- ness. At Kane Spring, thin-bedded, siliceous, cherty limestones, with yellow, limy shales, belonging to this upper series, contain poorly preserved fossils, referre o I the clips on both sides appearing to be about 15°. Farther south, however, these dips gradually increase, and in one conspicuous peak in the south- central part of the range the strata are sharply compressed, forming a type of structure quite unusual in the desert ranges, but still present, especially in certain ranges Ij'ing closelj^ east of the Sierra Nevada.'' It has already been noted that the limestone which forms the Mormon Range seems to be conf ormabl}^ over- lain, on the flanks of the range, by a Tertiarj^ rhyolite and rhyolite tuff series.* That there was an erosion interval between the Carboniferous and the rhyolite period is shown by the irregularity of the contact, as, for ex- ample, at the mouth of Hackberry Canyon, where the rhyolite is found on one side of the canyon and not on the other. Nevertheless, most of the folding which brought about the forma- tion of the range certainlj^ did not begin until after the rhyolite period. The limestones must also have taken j)art in later movements, evidenced by fold- ing in the postrhj^olitic Tertiary rocks to be described in considering Meadow Valley Canyon, which are separated from the rhyolites by an unconformity. Thus the total amount of folding in the range is the combined result of all the Tertiary movements, which, from phe- nomena observed in Meadow Valley Can- yon, seem to be still in progress. MUDDY RANGE. The Muddy Range is a soutliAvard con- tinuation of the Mormon Range, being separated from it only by the gap of Muddy Creek. It extends south to the Colorado River, where it is separated from the Colorado Range hy Boulder Canyon. "C. D. Walcott: Am. Jour. Sci., .M series, Vol. XLIX, 189.5, p. 169. (fSee description of Meadow Valley Canyon, p. 140. SPUKR.] MUDDY RANGE. 137 SEDIMENTARY ROCKS. The Carboniferous strata of tlie Mormon Rani>e appear in tlie field to be continuous into the northern end of the Muddy Range. The soutliern portion of the range, however, is represented on the Wlieeler survey geologic map as composed of Triassic rocks." At the extreme southern end of the range, in Boulder Canj^on, only the Archean igneous rocks and gneisses are exposed, as described by Mr. Gilbert.* These are overlain by Tertiary- lavas. The following observations were made b}^ Mr. R. B. Rowe'^: CARBONIFEROUS. About 4 miles west of Logan, on Muddj" Creek, there occurs prob- ably Carboniferous limestone, overlying Mesozoic sandstones and conglomerates. Between Logan and Weiser's ranch, above the Nar- rows, Paleozoic limestone is again shown, being brought against the Mesozoic by a heavy fault. The Mesozoic also seems to lie conform- ably upon the limestone on one side of the fault plane. Fossils collected 3 miles west of Logan post-office by Mr. Rowe were determined by Dr. Girty a"s rather doubtfull}^ Permian. MESOZOIC. At the first locality above-mentioned, 4 miles west of Logan j)Ost- office, there are bright-red hills of massive cross-bedded sandstone showing no bedding iDlanes. West of these hills are softer red-clay beds, bluish shale beds, gray conglomerates, and thin limestone beds. Some of the limestone beds contain fossils, regarded by Mr. Rowe as Jurassic. Mr. Rowe's collection was examined by Mr. T. W. Stan- ton, who referred it possiblj^ to the same horizon as fossils from simi- lar beds in the south part of the Spring Mountain Range. He believes the horizon is not younger than the Triassic and may be as old as the Permian, but as the forms are all new no definite statement can be made. One of the conglomeratic strata contains considerable petrified wood. From some of the darker shales of the Mesozoic some narrow seams of coal, from one-half to one inch in thickness, have been reported. At the second localitj^ mentioned above, between Logan and Weiser's ranch, the Mesozoic again appears, lying conformably upon the limestone.^ TERTIARY. On the north side of Muddy Creek, above the old California cross- ing, are the red, j^ellow, and bluish deposits of the Tertiary. On the nU, S. Geog. Surv. W. One Hundredth Mer., Atlas Sheet No. 66. h Idem, Vol. Ill, p. a5. (■Taken from his notebooks after Mr. Rowe's death, by the writer. f' This Mesozoic is mapped as Triassic to conform with the Wheeler survey mapping in the southern part of the I'ange. It will be ob.3erved, however, that these beds may be, in part at least, the same as those mapped in the Spring Mountain range as Jurassic. 138 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. south side, and iindoubtedl}^ connected with these, are clay deposits of considerable thickness and extent. Between Logan and Weiser's ranch red and yellow clays and ancient talus deposits, now hardening into conglomerates, lie un conformably upon the Mesozoic. IGNEOUS ROCKS. In the northern part of the range the writer* observed volcanic rocks overlying the folded strata. On the Wheeler maps patches of basalt are shown in a similar relation in the southern part of the range, and these extend, as described by Mr. Gilbert, to Boulder Canyon. STRUCTURE. At the northern end of the range the stratified rocks seemed from a distance to dip eastward at high angles, but the actual structure w^as not made out. The folding probablj^ decreases rapidly toward the south. The following observations were made by Mr. R. B. Rowe : About 4 miles west of Logan there is probably a fault between the Paleozoic and the Mesozoic. The Mesozoic dips quite sharply to 13 2 ■* Fig. 11.— Cross section of Muddy Range, after R. B. Rowe. 1. Carboniferous limestone. 3. Mesozoic conglomerates, shales, and limestones. 2. Massive i-ed Mesozoic sandstone. 4. Tertiary clays and consolidated talus deposits. the west. Between Logan and Weiser's ranch the fault is beautifullj^ shown, bringing the Mesozoic against the Paleozoic limestones. On the west side of the range the Mesozoic seems to line conformably upon the limestone. The dip of the limestone is almost perpendicu- lar, while the Mesozoic lies against it, with a much lower dip, on the east side. (See fig. 11.) COLORADO RANGE. The Colorado Range is a southward continuation of the Muddj^ Range, and is separated from it by the Colorado River at Boulder Canyon. Its geology is represented on the Wheeler geologic atlas aJ. E. S. SPURR.] RANGES OF SOUTHERN NEVADA. 139 (slieet No. 66) as consisting essentiallj^ of an Arcliean core overlain by lavas and flanked }:>y Pleistocene detritns. ELDORADO RANGE. The Eldorado Range lies west of the Colorado Range, being separated from it by the Colorado River. As represented on the Wheeler atlas, its geology is abont the same as that of the Colorado Range. MEADOW VALLEY CANYON. TOPOGRAPHY. Meadow Valley Canyon is cut in the bottom of a broad north-south plateau vallej", which separates the Meadow Valley Range on the west from the Mormon Range and other mountains on the east. Although the canyon is dry for long stretches, yet such water as may flow in it is carried to the Colorado, of whose drainage the canyon forms a part. That portion of the valley which is here described is about 90 miles in length, extending from the vicinity of Pioche soutliward to West Point or Moapa. The canyon begins a short distance south of Pioche, and grows continually deeper toward the south. The continuation of Meadow Valley northward from Pioche is called Duck Vallej^, which is a tj-pical broad desert valley with no canyon. Opposite Pioche the appearance is already unlike that of the tj^pical desert vallej" of the region. There comes in a central narrow strip of level wash, marking the channel of drainage, while on both sides there rises to the mountains a detrital slope, which, unlike that of most Nevada valleys, is cut up into low hills. To the south the central drainage channel becomes deeper, the slopes sharper, and the hills more cut up. To the north the reverse is the case, until the valley appears almost flat, like the typical Nevada valley. From the vicinity of Pioche the incision of the drainage into the valley bottom becomes progressively more pronounced southward, until some few miles south of Panaea a box canyon begins, which soon attains a depth of 500 feet, and, within a few miles, 1,000 or 1,500 feet (PL VI, A). Some miles south of here, at Kernan's ranch, the canyon walls are estimated to be fully 2, 000 feet high. Still farther south, and just northeast of the Mormon Range, the valley widens out into a broad basin inclosed by mountains, for a few miles below which another shorter and somewhat lower canj^on is entered. Below this is a broad, gently sloping plateau- valley, in which the drainage chan- nel, though generally sharp, is shallow. This plateau gi'ows wider toward the south, as also the vallej^ which is cut in it. At the junction of the Muddj^ Creek and Meadow Creek drainage, near West Point or Moapa, the valley is 2 miles wide. Meadow Vallej^ Canj'on ofl"ers exceptional advantages for study. Most of the Nevada deserts are nearly level, and appear to be filled with Pleistocene accumulations, mostly subaerial. Observations in 140 GEOLOGY OF NEVAIVA SOUTH OF 40TH PARALLEL, [bull.208 some of these flat valleys, however, show that Tertiary rocks crop out in patches and that the Pleistocene cover is onlj^ a veneer. But, tliere being no drainage, in these valleys, there is very rarely an opportunity to find sections cut by running waters, so as to study the real valley filling. In Meadow Creek Canyon we have such an opportunity. The slight incision in the valley opposite Pioche grows to a continuous canyon 1,000 or 2,000 feet deep, whose walls afford excellent sections of the Tertiary sediments and lavas which constitute the real valley filling between the ranges of Paleozoic strata on either side. PALEOZOIC ROCKS. On the west of the valley, the Highland and Meadow Valley ranges, and on the east the Mormon Range, are composed of Paleozoic strata, the Highland Range being chiefly Cambrian, the rest largely Carbon- iferous. Between these mountain ranges the valley probably existed before the deposition of any of the Tertiarj^ rocks. RHYOLITE. The oldest of the post-Paleozoic rocks noted in Meadow Valley Can- yon was j-hj^olite. This Avas flrst encountered at the ui)per end of the canyon, near Yokum's ranch, where it occurs in rugged outcrops. A specimen proved to be a siliceous biotite-rhyolite. This has been eroded, and against it has been laid down a horizontally stratified white rhyolite sandstone derived from it. The sandstone is hardened and forms cliffs and buttes. The rhyolite is thoroughly decomposed. South of here, the basal rhyolite may be traced for some short dis- tance in the canyon walls till it sinks below the bottom of the canyon and gives place to an enormous series of the overlying rhyolite sandstones, which contain interbeclded thin sheets of rhj^olite. There are in many places evidences that the basal rhyolite was eroded before the deposition of the overlying detrital series, for the latter often rests in the irregularities of the surface offered bj^ the former. The rhj^o- lites and the overljang derived sediments are folded throughout (dip- ping exceptionally as much as 30°, though usually deviating only slightly from the horizontal), and are often faulted, small faults being numerous, and those of KX) feet or more being not infrequent. The basal massive rhj^olite was again observed at Hackberry Can- yon. In the section afforded here the lowest member is a white bio- tite-rhyolite, thoroughly decomposed. At the mouth of the canyon this rhyolite overlies the Carboniferous limestones conformably', the whole being folded together and unconformable to the overlying for- mations. RHYOLITE-SANDSTONE SERIES. At the upper end of Meadow Valley Canyon, at Yokum's, the con- solidated rhyolite sandstone and conglomerate whicli overlies the massive rhyolite has alreadj^ been described, and also its occurrence in the canyon immediately^ to the south, where it succeeds the basal U. S. GEOLOGICAL SURVE ULLETIN NO. 20S PL. VI A. RHYOLITE WALLS OF MEADOW VALLEY CANYON AT CARSON'S RANCH. B. PLIOCENE CONGLOWIERATE IN MEADOW VALLEY CANYON AT CANE SPRING. SPURK.] MEADOW VALLEY CANYON. 141 lava above an apparent erosion gap and is folded with it. The rhj'olite-saudstone or tnff series is overlain unconformably by ande- site, and is also cut by thin intrusive sheets of it. There appears also to have been considerable disturbance even during the deposition of the rhyolite-sandstone or tuff series, which is expressed by slight erosion gaps and irregularities between adjoin- ing beds. During the deposition of this series, therefore, periodic effusion of thin sheets of lava and erosion seem to have gone on simultaneousl3^ Some of the thin rhyolite sheets rest one upon another with diverging angles of banding, indicating to the observer Fig. 12.— Sketch section of east wall of Meadow Valley Canyon just south of Carson's ranch, showing unconformity between rhyolite sands and overlying dacitic lavas. at first sight an unconformity, since they have the appearance of being white stratified rock. This series was estimated to be 4,000 feet thick, and is exposed soutliAS'ard to a point about 45 miles south of Pioche, where it gives place, on account of the general southerl}^ di]3 of the folded beds, to later overlying sediments and lavas. ANDESITE-LATITE SERIES. There is found, overlying the rhyolite-sandstone or tuff series, at Yokum's ranch and in the canj^on to the south, several hundred feet of basic lava, specimens which proved to be in gen- eral bronzite-biotite-ande- site. A specimen coUecte;! just above Yokum's, prob- ably from the same gen- eral series, is biotite-horn- blende-C[uartz-latite. This andesite-latite se- ries rests unconformably upon the basal rhyolite or on the overlying rhyolite tuff (fig. 12) and also intrudes them in thin intercalated sills (fig. 13). From the northern end of the canyon the andesites were not observed for many miles southward, but in Hackberry Canyon they were again found exposed in exceptionally good section. Here they overlie the basal rhyolite unconformably, and are themselves tilted so as to be unconformable below the overlying sands and gravels. At Fig. 13. — Sketch section of west wall of Meadow Val- ley Canyon at same locality as flg. 12, showing intrusion of overlying sheet of dacitic lava into underlying rhyolite sands. 142 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. this point, as also at the northern end of Meadow Valley Canyon, the andesite contains considerable masses of volcanic breccia. It is con- sidex'ably decomposed, though not so much as the underlying rhyolite, and specimens proved to be pyroxene-andesite. REDDISH DACITES AND RHYOLITES AND ASSOCIATED SEDIMENTS. In the southern half of the northern portion of Meadow Valley Canyon, above the open basin to the northeast of the Mormon Range, the andesites were not observed; but the rhyolite sandstone or tuff formation was found to be overlain by beds of brown and yellow tuff, containing a variable amount of red lava, in the form of sheets. The great variability in thickness of the lava sheets, and, therefore, of the interbedded sandstones, makes a study of the series very difficult, no two sides of the canyon ever matching; but, so far as examined, the Scale Fig. 14. — Sketch of east side of Meadow Valley Canyon near locality of figs. 12 and 13, showing contact of imderlying rhyolite and overlying dacite, with no rhyolite sands between. volcanic rocks found in this upper reddish series are in part biotite- hornblende-dacite and in part pink rhyolite. It is not plain in the field whether this series of dacites and reddish rhyolites is older or younger than the andesites, for the two are not found together; but from the fact that the andesite is often found resting directly upon the basal rhyolite, it is inferred that it is probably older than the reddish dacite-rhyolite series. Between the series of red lavas and yellow-brown tuffs and the underlying series of white rhj^olites and white tuffs there is a marked unconformity and erosion gap (fig. 14). The dacites and reddish rhyolites not only form interbedded sheets contemporaneous with the yellow-brown tuffs, and furnish many of the pebbles in the associated gravels, but they have cut the same gravels and tuffs as intrusive sills, which are often of considerable thickness. Thus there are exposed sections in the canyon walls with the reddish volcanics at the base and the j^ellow-brown tuffs above, giving a false appearance, as if the sediments were younger than the lava. SPTTRE] MEADOW VALLEY CANYOJSI. 143 At one locality, near Kernan's ranch, the brown tuffs and red lavas were seen to be overlain bj^ a flow of pyroxene-olivine-basalt, whose lower boundary is irregular. This whole series of red lavas and brown tuffs is broadly folded, although not so much as the rhyolitic series below. It has in general a southerly dip, and where the canj^on gives way below Kernan's ranch to the broad, level basin which lies northeast of the Mormon Range it is overlain unconformably by horizontal brown sandstone or tuff belonging to a later epoch. PLIOCENE BEDS. In the valley near Panaca the stream bottom has on both sides scarps 60 to 100 feet high, consisting of horizon tallj^ stratified silt and sand. These sediments are sometimes green and yellow and pass into rhyolitic arkose. The scarps are cut down in a level valley plateau which has an elevation of about 5,000 feet; and from here on both sides a succession of benches, more or less dissected, rise to the moun- tains. The highest well-marked bench was estimated at 6,000 feet. In the northern portion of Meadow Valley Canyon, between Carson's and Kernan's ranches, tlie different series of interbedded lavas and tuffs above described, which are all more or less folded, give way for a few miles on the west side of the valley to a deposit of about 2,000 feet of clean, brown volcanic sandstone and tuff, beautifully stratified horizontally, and extending to the top of the hills. The deposits are unfolded and unbroken, dipping south about 2°, and having a maxi- mum elevation of about 5,500 feet. In the upper part of this sand- stone series there seems to be a few sheets of rhyolite and basalt, the basalt being the younger. South of Kernan's ranch a series of brown, horizontally stratified, volcanic sandstones or tuffs comes in uncomformably above the slightly folded red lava and brown tuff series, and fills the broad basin which lies northeast of the Mormon Range. Of these horizontal sand- stones there is shown in the bottom of the valley a thickness of about 800 or 900 feet, although neither the bottom nor the top was seen. Below the sandstones are barely exi)osed horizontal conglomerates, well indurated, and containing pebbles of various sizes up to 2 feet in diameter. This sandstone series continues south, and lies up against the slopes of the Mormon Range to a height of about 2,000 feet above the valley or about 5,500 feet above sea level. The lower portions of the sandstone are indurated, while the upper parts are softer. They are often honeycombed i;i consequence of unequal consolidation and erosion. In one locality they are overlain by a sheet of very recent tordrillite. These horizontal rocks acquire a slight wavy structure on approaching the spur of Paleozoic limestones which constitutes the southern barrier of the basin. There are developed gentle folds with axes parallel to the spur, and dijjs averaging not more than 10°. 144 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. Close up to the limestone buttress the folding is somewhat closer, and the strata have a wrinkled appearance. At Hackberry Canyon the same series of horizontally stratified con- glomerates and soft sandstones overlies the pyroxene-andesite, from Fig. 15. — Sketch section of south wall of Hackberry Canyon near junction with Meadow Valley Canyon, showing Pleistocene faiilts and simple fault scarps. 1. Carboniferous limestone. 2. Rhyolite and derived sediments (probably early Tertiary). 3. Consolidated honeycombed conglomerate and sandstone (probably Pliocene). 4. Pleistocene faults. which it is separated by an unconformity and an erosion gap. At the mouth of Hackberry Canyon the same series is found, honeycombed and overlying unconforiiiably the upturned basal rhyolites. Both the horizontal conglomerates and sandstones and the underlying rocks 2 4 1 Fig. 16.— Sketch section of north wall of Meadow Valley Canyon, 3 miles southwest of mouth oJ Hackberry Canyon, showing a pre-Pliocene fault. 1. Interbedded pink and yellow sandstones, sandstone shales, and bluish-green siliceous limestones. 2. Homogeneous thin-bedded siliceous limestones (Carboniferous). 3. Pliocene (?) conglomerate. 4. Pre-Pliocene fault. have been displaced by recent faults, which are directly expressed ii the topography (fig. 15). Farther south, a short distance down th( main Meadow Valley Canyon (or, as it is called at this point, Mormor Canyon), the liorizontal conglomerate overlies unconformably th( SPUKR.] MEADOW VALLEY CA^YON. 145 Paleozoic limestones and sand- stones. At this point a fault lias displaced the Paleozoic rocks, but not the overlying conglomerates, showing that it occurred before the deposition of the latter (fig. 16). A short distance south of here the horizontal sandstone is brought to the bottom of the canyon by the dipping down of the contact be- tween it and the lower formations, and from liere to the neighborhood of Moapa or West Point it is the principal formation exi^osed in the valley, the older Tertiary deposits not being observed and the Pale- ozoic rocks only in patches. Froui Kane Spring southward to Grapevine Spring, a distance of about 3 miles, there is a ver}^ inter- esting section (fig. 17). Above the upturned and eroded Paleozoic limestones occur the consolidated brownish sandstones, grits, and conglomerates of the horizontal se- ries. The conglomerates contain pebbles of limestone, chert, and quartz from the Paleozoic series, white rhyolite from the basal rhyo- lite series, and characteristic red lava from the dacite-rhyolite series (PI. VI, B). There has been a slight local folding of the brown sand- stones and conglomerates, Avhich seems to have been partly caused by the advent of a considerable sheet of rhyolite. This rhyolite overlies the sandstones and has also cut into them as sills. Prob ably, however, part of the fold, iug took place before the intru- sion. At Grapevine Spring there has been a late faulting which has disj^laced the lava as well as the sandstones, and here also the up- turning of the strata has been ^ w a £ -g. O o 2 o cc Jg 'ftj'Vot'-"*' '?^5'M V tir I lU Bull. 208—03- -10 1-^6 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. greatest, resulting in a local dip of as much as 45°. Lying upon the uj)turned edges of the brown sandstones here, and also upon the later rhj^olite, is a series of consolidated grits and conglomerates, distinguished bj^ a gray color as opposed to the reddish and brown colors of the beds below (fig. 18). Southward from GraiDevine Spring to Moapa, the horizontal gray sandstone and conglomerate is contin- ually observed overlying the red and yellow series, which is again horizontal and mostly conformaljle to it. The very slight folding of all the beds which have been described under the last head separates them from all the underlying uncon- formable Tertiary series. Their position, structure, and distribution show that they are probably lake beds, and, indeed, they lie, partly Scale 4ofeet Fig. 18. — Sketch section of west wall of Meadow Valley Canyon at Grapevine Spring, Enlarged: from fig. 17. Showing fault gullies in Pliocene rocks. at least, in inclosed rock basins. These beds are provisionally referred to the Pliocene. « PLIOCENE RHYOLITES. In the section between Kane Spring and Grapevine Spring the ^ moderately tliick sheet of rhyolite above noted is of an age intermedi- ate between the lower brown Pliocene sandstone series and the upj)er gray Pliocene series, since it overlies the one and underlies the other. It is a glassy rock, and veiy little can be told of its composition. PLEISTOCENE RHYOLITE AND BASALT. At several points very recent lavas are seen, which form the latest phase of volcanic activity in this region. In the canyon near the northern end of the broad basin which lies northeast of the Mormon Range the topmost rock at one i^oint was found to be a sheet of "See description of Virgin and Mormon ranges, pp. 131 and lo.'). SPURR.] MEADOW VALLEY CANYON. 147 pyroxene-olivine-basalt, overlying with an irregular contact strati- tied volcanic sand aiaparently belonging to tlie dacite-red rhyolite period. Near the southern end of the same basin a thin sheet of glassy tor- drillite comes down into the valley, covering the hills in such a way as to show that the present topograj)liy was developed before the lava effusion. At Hackberr^^ Canj'on thin sheets of glassy lava overlie the hori- zontal Pliocene sandstones and conglomerates. Specimens of these sheets, taken at different but neighboring points, proved to lie tor- drillite and pyroxene-olivine-basalt. The two seem to be practically contemporaneous, and both must be regarded, from their position and Fig. 19.— Sketch section of wall of Hackberry Canyon at Hackberry Spring. 1. White decomposed rhyolite. 2. Pyroxene-andesite. 3. Conglomerate and soft sandstone (Pliocene ?). 4. Thin-bedded, slaggy olivine-basalt (Pleistocene). 5. Thin-bedded slaggy tordrillite (siliceous rhyolite ) (Pleistocene.) their relation to the underlyius tocene (fig. 19). rocks and to the tojiograph}^, as Pleis- PLEISTOCENE GRAVELS. Through all the rocks previousl}^ described, except part of the Pleistocene rhj^olites and basalts, the drainage has cut a canyon in places as much as 2,000 feet deep. The detritus removed b}^ this cutting has chiefly been carried down the valley and out to the Colo- rado River, but a certain portion still floors the vallej^ bottom. SEQUENCE OF EVENTS. Out of the complicated conditions observed at so many points in the valley of Meadow Creek, the following rough sequence of events may be provisionallj^ laid down : 1. Deposition of the Paleozoic series of quartzites and limestones. 2. Elevation of this series to a land mass and the erosion of the rocks to produce a system of mountains and valleys. This was attended hy little or no folding. 3. Pouring out of great masses of white biotite-rhyolite (early Tertiary.) 4. The formation of a series of water-laid rhvolitic sandstones and 148 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. tuffs, interbeclded Avith thin sheets oL" rhyolite and rhyolite bveccias. This wliole series is ronglily estimated at 4,000 feet thick and at the top contains relatively more tuffs, while at the bottom there are rela- tively more lavas. Several slight unconformities and manj^ slight erosion gaps occur in the series. 5. Folding to a considerable degree of the whole crust. 6. Explosive eruptions of pyroxene-andesites and latites of mod- erate extent. 7. The formation of a series of water-laid brown volcanic tuffs or sandstones and breccias, with interbedded quartz-bearing volcanics, chiefly dacites and reddish rhyolites. The sandstones were relatively thick at the bottom of the ^series, the volcanics at the top. The entire thickness of the series is estimated at 3,500 feet. There are some petty erosion intervals. 8. General folding, comparatively gentle. 9. Deposition of at least 2,000 feet of brown or red conglomerates and soft sandstones, which are accompanied by very few volcanic flows and so are distinct from the preceding formations. They have remained nearly horizontal and are probably, in large part at least, lake beds. They have been referred to the Pliocene. 10. Drainage of the Pliocene lake, erosion and slight local folding in the Pleistocene. 11. Outpouring of thin sheets of rhyolite, tordrillite, and pyroxene- olivine-basalt. 12. The formation of a small amount of high stream gravels. 13. Cutting down of the canyon bed to its present position. The thickness of the basal rhyolite is not known. A^ver}^ roughly estimated section of the overlying formations is as follows: Section in Meadoio Valley Canyon. Feet. Rhyolite tiTff series 4,000 Andesite : 600 Red lava and 'sandstone .__._. 3, 500 Pliocene sandstones and conglomerates ... . . 2, 500 Total 10,600 The succession of lavas, so far as can be made out in this confused section, is as follows: Biotite-rhj^olite, p^a-oxene-andesite, biotite- hornblende-quartz-latite, biotite-hornblende-dacite, quartz-latite or red rhyolite and tordrillite, pyroxene-olivine-basalt, glassj^ rhyolite or tordrillite. MEADOW VALLEY RANGE. The Meadow Yalloy Range lies oi)posite the Mormon Range, on the west side of Meadow Valley. It is comparatively low and irregular. At the north end it i)asses into tlie Highland Range and at the south SHL'RR] MEADOW VALLEY RANGE. 149 into Las "S^eg'as Range, with which it forms a V. Near this point it lioeonies broader and divides into several parallel petty ridges. SEDIMENTARY ROCKS. The Meadow Valley Range is composed chiefly of stratified rocks. CAMBRIAN. I'he mining camp of Delamar is situated on the western slope of the Meadow Vallej' Range. According to Mr. Emmons^' the range here consists of limestones underlain by heavy quartzites, these for- mations corresponding to the Cambrian quartzites and the limestones. There is a belt of shale, as at Pioche. These rocks are continuous northward into the Highland Range, but on the east are overlain by later volcanics. CARBONIFEROUS. Along the road which crosses the range from Moapa toward Pah- ranagat Valley an excellent section is obtained. Tlie rocks are Paleozoic limestones and form two synclinal ridges, with an interior anticlinal valley between. The eastern part of the section con- sists of rather thin-bedded limestone, full of chert nodules. These apparently overlie the strata of the westernmost ridge, which are dark-blue, semicrystalline limestones, also full of chert nodules, and containing some quartz veins. This is often fetid, and is more mass- ive and of older appearance than the other limestones of the section. Where the road cuts through the low eastern ridge the follow- ing Upper Carboniferous fossils were found, as determined by Dr. Girty: Fusiilina cylindrica. Archaeocidaris sp. Productus pratteniamis. Prodtictiis semiretictilatus. From the apparently lower rocks of the western ridge the following fossils were collected (also Upper Carboniferous): Zaphrentis sp. Productus? sp. Spirifer sp. Seminula sp. Macrocheilina? sp. Between the western ridge and the eastern face of the New Moun- tains to the west, which are an important branch of Las Vegas Range, a low ridge runs along the middle of the valley, joining the more massive mountains on the south at the angle of the V. This ridge a Oral oommunication. 150 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. is composed of fetid tliin-bedded limestones, like those just described. The following- fossils were found by Dr. Girty to be Upper Carbon- iferous : Fusulina cylindrica. Syringopora niultattentiata. Productus semireticulatus. Productus prattenianus. Pleiirotomaria sp. PLIOCENE. The Pliocene of the southern portion of Meadow Valley'^ extends westward and forms the flanks of the Meadow Valley Range, abut- ting nnconformably against the upturned Paleozoic limestones. The rocks consist of horizontal red and white sandstones and occasional conglomerates, varied a short distance east of Moapa by a white con- solidated volcanic ash. The Pliocene strata occupy a broad belt running north and south. They are locall}^ slightly folded, dipping as much as 10°, but in general are horizontal. On the western side of the range, in the bay between it and the New Mountains and Las Vegas Range, the same Pliocene sandstones occur. Some distance north from Moapa and just northwest from Hack- berry Spring, as seen from Meadow Valley, the Pliocene deposits seem to rise along the flanks of the Paleozoic Range until they occupy broad areas covering the limestones on the summits of the range, they themselves being capped by volcanics. IGNEOUS ROCKS. In the northern half of the range a great part of the rocks exposed at the surface seem to be volcanics, undoubtedly belonging to the Tertiar}^ and Pleistocene flows already described in Meadow Valley Canj^on. Thej^ probabl}^ are associated with Tertiary sediments derived from them, like the beds in the locality mentioned. STRUCTURE. The northern end of the range seems to be chiefly volcanic, from which the underlying Paleozoics emerge in places. South of here appear volcanics and associated Tertiary sediments, and the main ridge in the whole southern part of the range consists of folded Paleo- zoic limestones. The structure in the Paleozoic limestones consists of open j)arallel anticlines and synclines, generally of no great width or depth. North of the valley of the Mudd}^ the central ridge is syn- clinal, with an anticline closely adjacent to it on the eastern flanks of the ridge. Irregularities in the erosion sometimes bring this anti- aSee descriptions of Meadow Valley Canyon, Mormon Range, and Virgin Range, pp. 131, 136, 143. SPCRR.] MEADOW VALLEY AND FAHROC RANGES, 15X eline to the crest of the ridge, as shown in a section observed northwest of Kane Spring. Just west of Grapevine Spring, however, the syncline forms the summit. South of Mudd}' Yalle}^ on the road wliich runs westward from Moapa, the bioadening and dividing range shows two principal synclinal ridges with an interven- ing nonpersistent anticlinal valley. The SA'ucline of the westernmost of these ridges appears to be continuous with the main sj^n- clinal ridge farther north. Besides these main folds several petty ones were ob- served to the east of the easternmost large syncline, consisting of slight alternating- anticlines and sj^nclines. In the whole section no less than six adjacent open folds were observed, the sjniclines gener- ally forming ridges, the anticlines depres- sions. West of the westernmost syncline, a low Carboniferous ridge in the valley has a westerly clip, and in the depres- sion between it and the synclinal ridge is an anticline, as is shown in the moun- tains which terminate the depression be- tween the two ridges a few miles farther south (fig. 20). PAHROC RANGE. The Pahroc is a comparatively short range of no great height, lying immedi- ately west of the Highland Range and having a due north-south trend. Its length is not over 25 miles and its width not more than 5 or 6 miles. Only the north- ern part of the range was seen by the writer, and that from a distance of several miles. IGNEOUS ROCKS. Mr. Gilbert^' rej)orts that the Pahroc Range, on the road from Hiko to Pioche, is of lava, which extends a number of miles north and south. Z I 't3 3 lA/icddy CreeTc jMoapa. '^ « U. S. Geog. Sui-v. W. One Hundredth Mer., Vol. Ill, p. 123. 152 GEOLOGY OF NEVADA SOUTH OB^ dOTH PARALLEL, [bull.208. SEDIMENTAPa" ROCKS. I As seen fi-oin the north, the northern end of the range is made up of stratified roeli;s of moderate-l}^ tliick bedding, evident!}" lime- stones. These rocks extend for some distance fartlier south. Judg- ing from the rocks found just north of liere, in the low hills Avhich have been described as forming the connection between the Pahroc Range and the southern end of the Egan Range a short distance northwest of Pioche," the rocks of the Pahroc Range thus exposed are perhaps, in part at least, Devonian. The Silurian may possibly be represented. STRUCTURE. The limestones which constitute the northern end of the range seem, when viewed from a distance, to be bent into a single, regular, anti- clinal fold, which strikes parallel to the north-south trend of the range. The summit of the range appears to com^jrise the axis of the fold, and from this the rocks dip on l)oth sides at a gentle angle, averaging about 15°. HIKO RANGE. The Hiko Range lies next southwest of the Pahroc Range, with which it is joined at several points by low connecting hills. It has a north-south extent of about 30 miles, and, like the Pahroc Range, its general trend hardly diverges from a due north-south line. On the west the Hiko Range is connected by a series of hills with the Pahran- agat Range, and this series of hills continued farther Avest connects these ranges Avith the Timpahute Range and the Worthington Moun- tains. Like the Pahroc Range, .the Hiko Range is comparatively^ Ioaa'. SEDIMENTARY ROCKS. Most of the Hiko Range is composed of limestone of Silurian and DcA'onian ages. Mr. Gilbert* first described Silurian fossils from Fossil Butte, just Avest of the main range. Subsequentlj^ Mr. Wal- cott ^ made an investigation of the paleontology here, and described many species of fossils. According to Mr. Walcott there is exposed in Fossil Butte the Pogonip limestone of the Eureka series, overlain by the Eureka quartzite. Near Hiko he found shaly limestone, OA^er- lain by arenaceous limestone carrying a DcA^onian fauna. IGNEOUS ROCKS. Accoi'ding to Mr. Gilbert,'^ there are a fcAV small bodies of laA^a in the range. a See description of Egan Range, p. 49. &U. S. Geog. Surv. W. One Hundredth Mer., A^ol. Ill, p. 181. o Mon. U. S. Geol. Survey Vol. XX, p. 195. d Op. cit., p. 123. SPUKR] HIKO AND PAHRANAGAT RANGES, 153 STRUCTURE. Mr. Gilbert « found in the Hiko Range north of Fossil Butte a westerly clip, but south of this point an easteii}^ dip. There has been no folding, and therefore* there is a scissors fault''' transverse to the range at about this point. This same peculiar structural feature, according to Mr. Gilbert, is characteristic of all the ridges west of here as far as the Tinipahute Range. PAHRANAGAT RANGE. The Pahranagat Range lies next southwest of the Hiko Range, with which it is connected at its northern end by Fossil Butte. From here it extends southward in a general south-southeasterly direction for about 40 miles, where it is separated from the Arrow Canj^on Mountains by a comparatively short transverse stretch of desert valley. The highest mountain in the range is Quartz Peak, at its northern end. SEDIMENTARY ROCKS. Mr. Gilbert^ found Silurian fossils in the northern end of the range. Mr. Walcot t '^' found on the eastern side of the Pahranagat Range limestones which he regarded as possibly belonging to the Lone Mountain series of the Silurian. In Quartz Peak, just west of here, he found a fine exposure of Silurian strata comprising the fol- lowing divisions: Section at Quartz Peak. Feet. Lone Mountain Niagara 535 Lone Mountain Trenton 515 Eureka 400 Pogonip . 750 Total '. 2, 200 South of Quartz Peak he found a great thickness of limestone, nearl}^ 8,000 feet in all, broken onlj'^ by thin beds of yellow sandstone, the heaviest not over 100 feet in thickness. In this g'reat thickness of limestone he found no lithologic variation sufficient to base divisions upon. From the fossils contained he found that the lime- stone ranged from Carboniferou-^ through the Devonian into the Silurian. It was impossible to draw any line of demarcation « U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 39. bThe writer has employed this term thinking that it was already in use. Mr. Gilbert, how- ever, who has examined the manuscript, believes that the term is original here, and it is there- fore defined as a fault whose movement is like that of a pair of scissors when opened, there being on the fault plane an axis where the differential movement is nothing, while on one side of this axis the movement is the reverse of what it is on the other. Therefore the rocks on the two sides of the fault plane will acquire tilts in opposite directions. <-Op.cit.,pp.l68,181. dMon. U. S.Geol. Survey Vol. XX, p. 196. 154 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. between the Silurian and Devonian, but dividing the rocks as well as might be the following thicknesses were fonnd: Feet. Carboniferous _ . 2, 160 Devonian * ._ _ . 5, 400 Silurian _._. 1,000 IGNEOUS ROCKS. Mr. Walcott noted occasional outbursts of acidic lavas in the Pah- ranagat Range, and Mr. Gilbert describes two large eruptions of rhyolite, one at the north end of the range and the other at Logan Pass at a cross fault. STRUCTURE. According to Mr. Gilbert the cross fault above-mentioned is a scis- scors'* fault, having such differential movement that all the strata to the north acquired a westerly dip, while those to tlie south are tilted toward the east. That portion of the range which lies north of the cross fault is divided into separate north-south ridges by north-south faults whose downthrow has been uniformly to the east. South of the pass the strata have a single, monoclinal, easterly dip. ARROW CANYON RANGE. The Arrow Canyon Range has not been visited and was onlj^ seen from some little distance. It is a continuation northward of that branch of Las Vegas Range which has been called the New Mountains. It has a general northwesterly trend, j)arallel with the main west arm of Las Vegas Range, and has a length of more than 20 miles. On the north it is separated from the Pahranagat Range by a nari-ow, transverse valley. As seen from several points, the Arrow Canyon Mountains are made up of stratified rocks, well banded, but eroded so as to form massive cliffs. This is the apijearance offered by the heavy Carboniferous limestone of this region, as shown just south of here in the New Mountains. It is possible, therefore, that the bulk of the range is Carboniferous. To the north also, in the Pahranagat Range, Carbon- iferous rocks are present in considerable quantity. The strike of the strata is parallel with the trend of the range. Along nearly the whole of its western side the rocks are seen to dip into the range eastward at angles of from 15° to 20°. Farther north an area of apparently horizontal strata can be distinguished; so that the general structure of the range maj'^ be synclinal, corresponding to that of the New Mountains to the south, or it may be a general monocline dippiug eastwardly, like the Pahranagat Range. a See p. 153 for definition. SPURR] AKKOW CANYON AND LAS VEGAS RANGES. 155 LAS VEGAS RANGE. Las Vegas Range forms an irregular group in the central portion of southern Nevada, lying just east of another irregular group, the Spring Mountain Range. Las Vegas Range has hardly any defijiite form, but a prolongation on the northwest gives it rather the aspect of having a northwesterly trend. This pixjlongation forms one arm of a rough V, of which the southern portion of the Meadow Valle}' Range forms the other, the two uniting in a rugged cluster of mountains in the neighborhood of Gass Peak. Bisecting the angle of the V is a high, rocky ridge, which was not delineated on the Wheeler survey maps, and which the writer will call, for the purpose of description, the New Mountains. It is peculiar that so prominent a ridge should have escaped map- ping, for it comprises some of the highest mountains in the southern part of the State. On the eastern face of the New Mountains is a sharp scarp of about 4,000 feet, rising from the foothills. This scarp is often perpendicular for great heights, and is apparently inacces- sible. The rocks are composed of massive limestone, beautifully banded. To the north the New Mountains become lower and are separated from the Arrow Canj^on Mountains, which are reallj^ a portion of the same general range, by a transverse valley. The south-^iBst face of Las Vegas Range, facing Las Vegas Vallej^ also possesses a steep slope, reaching 45° at some points. No igneous rock whatever was found in Las Vegas Range. SEDIMENTARY ROCKS. CAMBRIAN. From a point about 6 or 7 miles north of Mormon Wells, which is on the wagon trail crossing the southern portion of the range in a north- easterljT^ direction, southward probably to the end of the range, the rocks consist chiefly of bristly weathering siliceous, crystalline, cherty limestone, often having a peculiar mottled structure, which is proba- bly due to the rock having been originally made up of coral, now recrj'stallized and unidentifiable. This rock is lithologically identical with Cambrian limestones in the Highland Range west of Pioche. On the divide south of Mormon Wells there are found thin, brown and red, sandy, and limj^ slates, changing to thin-bedded limestones. These contain fossil remains, which are determined by Mr. Walcott as belonging above the OleneUus zone and probably to the Middle Cambrian. Fragments of white quartzite were found in the drift here, which also suggest the existence of Lower Cambrian quarzites in the mountains. The same ancient-appearing limestones are continuously exposed along the road above mentioned, southwest nearly to Las Vegas Val- ley. At this point they give way to the underlying Silurian. 156 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. Mr. R. B. Rowe noted that the first ridge west of Sheep or Gass Mountain (which ridge is here considered the northernmost part of Las Vegas Range) consists of beds of dark-blue and gv&y lime- stone, with white and reddish sandstone. Fossils collected in this locality were found b}' Dr. Girtj^ to be chiefly Devonian, but to con- tain one Cambrian specimen. Therefore, probably both the Cambrian and the Devonian are here represented. SILURIAN. In the vallej^ just northeast of Gass Peak, at the locality above mentioned, occur cherty, blue-graj^ and siliceous, sometimes green and shaly, limestones similar to those of the Cambrian. The few,^ fossils obtained from these rocks are regarded by Mr. Walcott as rep- resenting H horizon about the base of the Pogonip (Ordovician). Mr. Walcott determined Ortliis perveta (?) and the tail of a trilobite belonging to the genus Batliyurus. From this point to the northwestern end of the range the rocks ■ appear to be all limestones, of the same ancient character as tlioise already described, as specimcKS obtained here and there show. Ai similar limestone extends still farther northwest into the southern end of the Desert Range, and was followed continually along Las Vegas- Valley to Indian Spring in the Spring Mountain Range. At Indian Spring iDrdovician fossils were found. About miles northeast of Corn Creek, near the mouth of the first important canyon, Mr. R. B. Rowe found about 200 feet of dark blue limestone, containing immense numbers of gasteropods of enor- mous size, together with a few corals. The fossils collected hy Mr. Rowe were determined bj' Dr. Girty as Ordovician. DEVONIAN. The existence of Devonian limestones in the ridge west of Sheep or Gass Mountain, at the north end of the range, has already beeni mentioned. CARBONIFEROUS. The Cambrian rocks in the neighborhood of Mormon Wells are apparently separated by a heavy east- west fault from the unmetamor- phosed massive blue limestones which make up the greater portion of the New Mountain ridge and the auxiliary ridges to the east. In one of these auxiliary ridges a collection of fossils was obtained, which were found by Dr. Girty to be Upper Carboniferous. No north-south faults were determined, and the gentle folding, resulting in slight, alternating synclines and anticlines, suggests that rocks of the same horizon make uji the New Mountains to the west. According to the notes of Mr. R. B. Rowe, the mountains east of Las Vegas contain the Lower Carboniferous, the Carboniferous red puRR.l LAS VEGAS KAISTGE. 157 3eds, and the Upper Carboniferous limestone, so far as can be seen Tom Las Vegas ranch. From Sheep or Gass Mountain, in Las Vegas Range, specimens of (xoniatites were brouglit and given to Mr. Rowe. The fossils seem to 3ome from a soft shale.'* About 2 miles west of Sheep or Gass Mountain, in a spur of that *ange, about 5 or G miles north of the road leading from Corn Creek j:o Indian Creek, fossils were collected which were determined by Dr. irty as Upper Carboniferous or Pennsylvanian, and in the same General region other fossils were collected which were determined. by Dr. Girt}' as Lower Carboniferous or Mississippian. The ridge con- "lists mainly of low hills, wliich are cut extensively by canyons. Terfianj. — -Mr. R. B. Rowe's notes on the Tertiary areas follow. lAt Las Vegas and in the immediate vicinity there are white beds of probabl}" volcanic ash. From the vallej^ some distance west of Las V^egas mastodon teeth were collected. About midwa}^ between Corn Creek and Tule Springs some mastodon teeth and bones have been found. They were situated in a clay bank some 10 or 15 feet high. East of the range, at the summit of the pa^ss between Las Vegas Valley and Muddj^ Creek, about 12 miles east of Las Vegas, are fed and yellow Tertiary beds which dip toward the Colorado River at an angle ranging from 4° to 5°.* The valley between Las Vegas, Tule Springs, and Corn Creek seems to be filled with lake deposits. About Tule Springs, and from there up the valley, are probably the remnants of an old, dry lake bed or playa. The deposits do not have the appearance of the Tertiary lake deposits, but resemble exactly the clay deposits in the present dry lakes. Underlying these is a gravel or talus deposit. The eroded drv lake beds extend froni Corn Creek to Indian Creek. PLEISTOCENE. In Las Vegas Vallej^ the Tertiary deposits so abundantly exposed in the region of Meadow Valley are hidden beneath Pleistocene accumulations. This valley is of the usual type of the desert valleys of Nevada, with gulch dumps fringing the mountains, and in the center a nearly level area of hard mud flats, or a playa. There has been no dissection of these deposits to reveal what lies beneath. STRUCTURE. The general folding in Las Vegas and New mountains has apparently resulted in a rough, shallow, disturbed northeast-southwest striking syncline. The nearly horizontal area in the central portion of the range « These maybe the same as some specimens of Goniatiies rec3ived by Dr. Girty from. Mr. Rowe's collection after the death of Mr. Rowe. They were considered by Dr. Girty as Lower (?) Carboniferous. ''These are the same as described by the writer under the head of 'Meadow Valley Range." 158 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. belongs in the trough of thes^^ncline, while at the northwestern end the dip of the northwest limb of the fold becomes 30° or 45° southeasterly, or even more. The sjaicliue is succeeded by a much sharper anti- cline along the narrow valle}^ separating the Desert and Las Vegas ranges. In the broad central portion of the syncline there has been irregular minor folding, chiefly along east-west lines, the dips gener- ally being under 15°. At the southern end of the range the general strike appears to become east and west, and the dip about 20° north. The main fold of Las Vegas Range, being at right angles to the general trend of the mountains, runs across Las Vegas Valley and is probably to be found in the Spring Mountain Range on the other side, where, indeed, it Avas thought to have been identified by the writer. Similarly, the various ijarallel ridges of limestone which run trans- verse to the general trend of the range are broken by the valley and find their continuation in the Spring Mountain Range opposite. Las Vegas Valley, therefore, differs from the most ordinary type in the Great Basin in that it is transverse to the general strike of the rocks. In the region north of Mormon Wells there is a marked change from massive, unaltered, blue limestones, probably belonging to the Carboniferous, to altered, ancient-appearing, crystalline limestones, associated with shales can-ying Cambrian fossils. The areas occupied by these different rocks may be easily sketched, since the erosion of each has resulted in peculiar forms. The Cambrian rocks have rounded topography, without scarps or evident structure, and weather brown, while to the north the blue-gray Carboniferous rocks have sharp scarped outlines with perfectly visible stratification. Inasmuch as the strike of the folds is here north and south, which carries the Carboniferous limestone directly into the Cambrian, there must be a fault between tlie two horizons, and this fault must have, as sketclied, a direction somewhat north of west. The vertical disj)lacement of the fault maj^ be several thousand feet and has resulted in a downthrow to the north. There is no distinct brealv in the topography along the fault line. The bold east face of the New Mountains suggests a more recent heavy fault, to whose displacement the scarp maj^ perhaps be directly due. The following notes on the structure were made by Mr. R. B. Rowe: A sketch of the mountains of Las Vegas Range east of Las Vegas shows a constant dip of about 40° to the east. A hypothetical fault is also shown, which has the effect of bringing up the lower strata on the east side. In ear Corn Creek the rocks strike east and west and dip uniformly 30 ° to the north. As has been noted, there is a^jparently a series of old, dry lake deposits in Las Vegas Valley, which are now being cut into by the arroyos. These, taken together witli the fact that the surface rises about 400 to 600 feet between Tule Sjarings and Com Creek SPURR.] TIMPAHUTE RANGE. 159 and that the same beds rise still higher bej^on«l Corn Creek, indicate a comparatively recent elevation of the upper end of Las Vegas Valley. On the east side of Las Vegas Range, the fact that the Tertiary beds dip slightly toward the Colorado at an angle of 4° or 5° suggests that the Las Vegas Range has been slightly raised since the general elevation of the region. TIMPAHUTE RANGE. The following summary of the Timpahute Range is taken from Mr. Gilbert's description." The Timpahute Range lies next west from the Pahranagat Range and immediately south of the Worthington Mountains. Its general trend is a little east of north and its length about 30 miles. The highest portion is Timpahute Peak, near the southern end. SEDIMENTARY ROCKS. At the south end of the range Mr. Gilbert * measured a thickness of 2,325 feet of strata showing the following section: Section at south end of Timpahute Range. Feet. 1. Heavy-bedded gray limestone, light and dark 400 2. Yellow argillaceoiis shale: a. Yellow shale, 350 feet .._ -. b. Yellow sandstone, 75 feet | c. Yellow and green shale, with fillets of , fossiliferons limestone | (Conoconjphe) , 500 feet J 3. Piarple, ripple-marked, vitreoiTS sandstone, with bands of siliceous shale. 1, 000 Total -. 2,325 The fossils found in the shales above the basal quartzite fix the formation as Cambrian, and the basal quartzite is the same as the basal quartzite of the Highland Range Cambrian section and also the Prospect Mountain quartzite at Eureka." The northern portion of the range does not appear to have been described. Both to the east and to the west of it, in the Worthing- ton Mountains and in the Pahranagat Range, are Silurian rocks, in part Lower Silurian. It is probable, therefore, that this north end of the Timpahute Range is in part Silurian and in part also Cambrian. IGNI]OUS ROCKS. According to Mr. Gilbert,'^ Timpahute Peak is the center of a massive eruj)tion of rhyolite, which connects with a similar eruption northeast of here in the Pahranagat Range by a line of volcanic hills which runs across the intervening valley. aJJ. S. Geog. Surv. W. One Hundredth Mer., Vol. III. 6Ibid., p. 169. cTbid., p. 181; C. D. Walcott, Bull. U. S. Geol. Survey No. 30, p. 30, Bull. 81, p. 156: Arnold Hague, Men. U. S. Geol. Survey Vol. XX, pp. 45, 189. ''Op. cit., p 123. 925 160 GEOLOGY OF NEVADA SOUTH OF 40TH PAEALLEL. [bull.208. STRUCTURE. The volcanic outburst at Tiinpaliute Peak, according to Mr. Gil- bert/' is on the line of a scissors fault, whicli has so displaced the strata that to the north of this fault they dip uniformly west while to the south thej^ dip nniformly east. This fault is on the same line as a similar fault northeast of here in the Pahranagat Range, and another still farther northeast in the Hiko Range, and in each of these ranges the peculiar tilting of the strata above noted is found. In the Timpahute Range the sedimentary rocks south of the line of faulting are separated by north-south vertical faults which have a uniform downthrow to the west. Mr. Gilbert gives a section of the range showing this structure. ORE DEPOSITS. In the Cambrian shales at the southern end of the range, according to Mr. Gilbert,^ are metalliferous veins. DESERT RANGE. The Desert Range is somewhat irregular and of moderate height. It is divided into two branches by an interior valley which reaches northward from the north end of the Spring Mountain Range. At its north end the Desert Range passes into the valley which sepa- rates the Timj)ahute from the Pahranagat Range. SEDIMENTARY ROCKS. The south end of the Desert Range was visited by the writer. It consists of altered, crystalline, light-gray limestone, brown weathei-- ing, often full of rounded, detrital quartz grains. There are also beds of black, dense limestone. Similar limestone contains Ordovi- cian (Pogonip) fossils in the western part of Las Vegas Range. This limestone series can be distinguished extending northward fully half- way to the end of the range, at least 20 miles. It is possible that it may contain some of the Cambrian limestones which are hardly separable lithologically from the overlying Silurian. Mr. F. B. Weeks'' followed along the west side of the range and crossed the north end, at Mud Spring, in 1900. He found the bulk of the range to consist of stratified rocks, which he was inclined to consider as Silurian and Devonian, while on the north end these strata are replaced by volcanic rocks. The following notes were made b}^ Mr. R. B. RoAve:'^ SILURIAN. About 8 or 9 miles northeast of Indian Creek, in the first range on the west side of the dry lake which lies east of Indian Creek, and about «U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, pp. ! Mbid.,p. 181. c Personal communication to the writer. f' Taken from his notebooks after his death by the writer. spiTRR.] DESEET AND REVEILLE RANGES. 161 •4 miles north of the road from Indian Creek to Corn Creek, tlie section consists chiefly of dark-bine limestone, with light-bine arenaceons limestones and shaly limestones with chert layers. There are also a few layers of white sandstone, resembling- qnartzite. Fossils collected were regarded by Mr. RoAve as Ordovician, and his impression was corroborated by Dr. Girty's examination. The rocks 4 miles east of Indian Creek are light-gray, arenaceons, and dark-bine limestones, with laj^ers of chert and white sandstone, which is nearly a qnartzite, as it is farther east. These rocks were regarded b}'^ Mr. Rowe as probably Lower Silnrian. DEVONIAN. Abont o miles northeast of Indian Creek, in low hills sonth of the road leading to the lower end of Pahranagat Valle}^ and north of the road to Corn Creek, fossils were found in loose blocks of dark-blue limestone. These were regarded by Mr. Rowe as Middle Devonian, and were determined by Dr. Girty as probably Lower Devonian. STRUCTURE. At its southern end the range is separated on the southwest from Las Vegas Range by a narrow anticlinal valley, the rocks of the Desert Range dipping northwest on the northwest limb of the fold. The general strike here is northeast, and a series of parallel ridges has been eroded parallel to the strike. The dip continues in the same direction as far as the interior valley dividing the two chief branches, but becomes flatter, and the strike swings around more toward the north. On the western branch of the range, as seen from the south, the rocks are j)artly horizontal and partly strike a little east of north and dip uniformly west at angles not exceeding 15°. The valley lying between the ridge lying west of Sheep Mountain and the range next west, or between Las Vegas Range and the Desert Range, was regarded by Mr. Rowe as anticlinal in structure." The mountains on the two sides dip in opposite directions. On the west- ern side Ordovician fossils were found ; on the eastern side Carbonif- erous and Cambrian. There are probably large and numerous faults concealed by the talus. There is a great deal of plainly observable faulting at right angles to the strike. These faults are generally not large, but are abundant.* REVEILLE RANGE. The Reveille Range is separated on the north from the Pancake Range by a narrow transverse gap at Twin Sijrings. It extends southeastward from here a distance of about 60 miles, running obliquely across to the Timpahute Range. "This is the same anticlinal valley that was previously observed by the writer (see above) (J.E.&.). bThis whole paragraph is from Mr. Rowe's notes. Bulk 208—03 11 162 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. TOPOGRAPHY. The range is somewhat irregular in its course and extent, which arises from its being made up largely of volcanic outbursts. This also accounts for the prevalent tj^pe of topography, which is similar to that of the Pancake Range to the north, showing low peaks and broad, gently sloping mesas, which are sharply cut into by the valleys eroded since the period of lava effusion. At one or two points, how- ever, such as that near the old mining camp of Reveille, xjatches of older Paleozoic strata, and of older volcanics than those which form tlie mesa-like forms, emerging from the younger lavas, offer a series- of sharp, irregular peaks and better developed valleys. SEDIMENTARY ROCKS. According to Mr. Gilbert," the Paleozoic strata which form the core of the Reveille Range are exposed at but two points, one at Reveille and the other 60 miles farther south. In both these cases the rocks dip to the west, the dip being steeper at the more southern exposure. At Reveille the strata are of limestone and quartzite. Fig. 31.— Generalized sketch cross section of Reveille Range near Reveille. 1. Paleozoic (Cambrian) quartzite (la) and limestone (lb). 4. Rhyolite sandstone. 2. Rhyolite. 5. Olivine-basalt. 3. Porphyry dikes. . 6. Valley wash (Pleistocene). The more northerly locality was Adsited by the writer, and so far as a hasty examination could determine, the lowest formation seems to be a hard white quartzite, surmounted by a dark-blue massive lime- stone, much altered and cariying only indeterminable fossils. As seen from Reveille, the mountain to the east seems to have at its base about 1,500 feet of quartzite, capped by 2,000 feet of limestone. The strike is north and south, the dip W. 15° or 20°. If the section is actually as supijosed, the rocks can hardly be other than the Cam- brian quartzite and limestone of the Eureka section.^ The strata are traversed by many i^orphjay dikes, probabl}^ con- nected with the rhyolitic outbursts. The rhyolite wraps around these limestone mountains in such a way as to show that they were already sharp peaks previous to the pouring out of the lava (fig. 21). nU. S. Geog. Surv. W. One hundredth Mer., Vol. Ill, p. 37. 6 Ibid., p. 1V9, Mr. Gilbert cites Prof. J. J. Stevenson as having recognized Carboniferous rocks at Reveille. In view, however, of the confusion of Carboniferoiis and older rocks at this period (several other Cambrian areas having been referred to the Carboniferous) and in view of the fact that the lithology of the region is that typical of the Cambrian here, but probably not chai'floteristic of the Carboniferous, the writer has decided to retain in the mapping the Cambrian color. SPURR.] EEVEILLE AND BELTED RANGES. 163 TERTIARY. In the transverse cut across the northern end of the mountain range at Twin Springs the section consists of volcanic rocks and water-laid tuffs and gravels derived from them. At the base of the section is altered biotite-rhyolite, and above comes about (300 feet of white rhyolitic sandstone. This is (japped by 100 feet of rhyolitic tuffs and gravels, surmounted by about 100 feet of angite-olivine-basalt. IGNEOUS ROCKS. As already stated, most of the range is made up of igneous rocks. Those Avliich outcrop most upon the surface appear to belong to the later, more basic lavas, of which the augite-olivine-basalt at Twin Springs is a member. This same basalt is found on the east of the higher mountains between Twin Sjirings and Reveille. Beneath this basic lava, however, the older biotite-rhyolite frequently comes to the surface and is distinguishable by its more rugged topograj)hy. RELATIVE AGE OF IGNEOUS ROCKS. In the section at Twin Springs it is shown that the rhj^olite is older than the basalt. Between Twin Springs and Reveille the intervening series of tuffs disappears with increasing elevation, and the basalt mantles around the base of craggy rhyolite eminences in sucli a way as to show that they were already mountaius before the basalt appeared. The disappearance of the intervening tuffs also suggests that the higher rhyolite ijeaks Avere mountains in the lakes in which the rhyolitic tuffs were laid down. ORE DEPOSITS. In the vicinity of Reveille are mines which formerl}^ were very profitable, but which are now almost entirely deserted. The mines are situated in a patch of limestone and quartzite surrounded by volcanic rocks, and the ores probably have genetic connection with the dikes which traverse the sedimentaries. I ^' BELTED RANGE. The Belted Range runs southward from the Reveille Range and forms, in its southern part, the eastern boundary of the Aniargosa Desert. It is somewhat irregular, but has a general north-south trend. At its northern end it is separated from the Reveille Range by a slight interval of low, lava-covered country, while at its south end it is separated from the low mountains Ijing north of Pahrump Valley by a considerable intervening area of Pleistocene subaerial deposits. Its name has probably been given to it on account of the horizontal banding visible for a long distance on its steep sides. \ 164 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. SEDIMENTARY ROCKS. CAMBRIAN. The Belted Range was crossed by Mr. Gilbert during his recon- naissance for the AVheeler survey. He notes that at White BlufE Spring and for several miles southward the range shows an axis of quartzite.*^ This he regards as the same formation as a similar quartzite recognized in the Timpahute Range, which is of Cambrian age. The whole southern portion of the range, as seen from the south, is : of stratified rocks, apparently chiefly limestones. It is probable that this portion of the range forms a part of the general Cambrian- Silurian area, which includes part of the northern end of the Spring Mountain Range, a large portion of Las Vegas Range, and at least the southern end of the Desert Range. IGNEOUS ROCKS. VOLCANIC ROCKS. Mr. Gilbert^ found that near White Bluff Spring the principal mass of the range was of lavas, which nearl}^ hid the Paleozoic axis. These lavas stretch northeastward and connect with those of the Reveille Range, and also extend westward, forming low mountains, which divide the Ralston Desert from the Amargosa Desert. In these mountains Fortymile Canyon is cut. They extend westward at least as far as Oasis Vallej^, which is the head of the Amargosa River ; and they stretch northward over the whole of the Ralston Desert. <^ STRUCTURE. The probable structure of the Paleozoic southern portion of the range could only be uncertainly made out from a distant view. In general, however, the rocks appear nearly horizontal, but they some- times dip as much as 15° at least. The general strike is i^arallel with the trend of the range. SPRING MOUNTAIN RANGE. The Spring Mountain Rauge is an exceedingly irregular-shaped group of mountains, lying southwest of Las Vegas Range, and sepa- rated from the Kingston Range, farther south, by the Pahrump Valley. The general trend of the range is northwest and southeast, and its length in this direction is about 60 miles, and at its northern end, in the neighborhood of Charleston Peak, the total width is as much as 30 miles. This peak constitutes the highest portion of the range, being 10,874 feet above the sea, and is a conspicuous landmark. This range is divided into numerous ridges, which run in many dif- a U. S. Geog. Surv. W. One Hundredth Mer,, Vol. Ill, p. 123. » Ibid. c See p. 182. SPURR] SPRING MOUNTAIN RANGE. 165 ferent directions without much visible system. At at least two points at the northern base of the range there occur warm springs, namely, Indian Spring and the spring at White's ranch in Pahrnmp Valley This is interesting, since the range contains few igneous rocks. SEDIMENTARY ROCKS. CAMBRIAN. The north end of the range was traversed from Indian Spring southwest, b}^ way of Hornet Spring, to White's ranch. At Indian Spring are limestones carrying Lower Carboniferous fossils, as deter- mined by Dr. Girty. Following up the canyon which leads southward to Hornet Spring a great thickness of limestones was passed through, all striking a little north of east, parallel in general with the north end of the range, and dipping northward at angles varying from 20° to 65°. The limestone is all thin bedded. North of the summit of the pass comes in a thin bed of vitreous quartzite. At the summit is a thick white vitreous quartzite, often coarse and nearly conglom- erate, beneath the limestone. Just south of the summit there is an east- west fault which cuts off the quartzite and again brings down the limestone into the section. In this limestone, at a point half a mile south of Hornet Spring, were found abundant fossils, which have been determined by Mr. Walcott to be Cambrian, probably Middle Cambrian. These fossils are in blue-gray semicrystalline limestone like that found above the quartzite north of the fault. It is probable, therefore, that some of the limestones exposed in ascend- ing the canyon north of the summit belong to the Cambrian, and that these pass upward into the Lower Carboniferous limestones at Indian Spring without any marked stratigraphic or lithologic break. The white quartzite at the summit is also probably Cambrian, since it underlies the limestones. The thickness of the section shown north of the fault has been estimated at about 17,000 feet, of which an estimated thickness of 2,000 feet ma}' be taken for the quartzite, leaving 15,000 feet for the limestones. The Cambrian limestones near Hornet Spring are continuous only a short distance south, when they give place abruptly to Carbonif- erous limestones, the two being apparentlj^ separated by an east- west fault, parallel with and only some 3 miles south of the one already mentioned. From this j)oint to the southern end of the range it is probable that no Cambrian rocks are exposed, since Carboniferous fossils are found at many points. Mr. R. B. Rowe's notes'* on the Cambrian may be summarized as follows : About 7 miles south of Indian Spring, in a high range of hills, were found greenish-yellow shales, with thin, dark sandstone bands a Made in 1900-1901. Taken from his notebooks, after his death, by the writer. 166 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 308. containing trilobite and linguloid shells. These were nnderlaiu by brownish massive limestone, containing great numbers of trilobite remains. These Cambrian rocks appear to be directly overlain by dark-bine and gray, iDrobably Carboniferous, limestones. The dip of \ the Cambrian rocks is due north, while that of the Carboniferous is to \ the south, suggesting an unconformity,, although the two formations are divided b}^ a covered wash 2^ miles Avide. The Cambrian may be I separated from the Carboniferous here hy a fault or bj^ an uncon- formit3^ In the whole Spring Mountain Range nothing was found between the Cambrian and the Carboniferous suggesting a hiatus between the two periods. On the southwest side of a traversed line from Indian Creek to Tule Springs (on the east side of Las Vegas Range), from a distance about 5 miles east of Indian Creek to about 5 miles west of Corni Creek, the low hills near the valley are Cambrian, and probablj^ some on the north side of the valley also. About 6 or 7 miles southwest of Corn Creek, on the south side of the valley, there is apparently a fault, bringing the Cambrian against what is i:)robabl3' the Carbon-i iferous (fig. 22). The Cambrian comprises a number of parallel ridges, with steep south-facing escarpments and with strata dii^ping; north. Between the ridges is a covering of talus. CARBONIFEROUS. At Indian Spring Lower Carboniferous fossils were found in a black, fetid, semicrystalline limestone with brown sandy beds. They were determined bj'^ Dr. Girty as follows: Ptilodictya sp. Chonetes sp. ProchictiTS cf. mesialis. Orthothetes 11. 8p. Dr. Girt}^ remarks that this fauna can not with certainty be placed* in the Lower Carboniferous, though it is probably of that age. These rocks probably constitute a relativel}'^ narrow strij^ at the northern end of the range, and are succeeded on the south by older strata, as above described. A few hundred yards south of the ranch at Indian Spring the fol- lowing Carboniferous fossils were collected by Mr. F. B. Weeks, in 1900," and were determined by Dr. Girty: Zaphrentis sp. Productns cf. P. Isevicosta. Rliipidomella oweni. Spmfer keokiik. Orthothetes insequalis. Spirifer near neglectiis. Prodnctella concentrica ? Seminnla liumilis. Prodiictns btirlingtonensis. Camarotoechia sp. Productus semireticiilatus. a Personal communication to the writer. SPURK.] SPRING MOUNTAIN RANGE. 167 At the same locality Mr. R. B. Rowe'* noted and collected Lower C'arboniferons fossils. The rock is massive and chert}' blue and gray limestone, with reddish and yellowish shalj^ and arenaceous laj^ers. The section is as follows from the top downward: Section near Indian Sjrrings. 1. Massive clierty blue limestone, poor in fossils. Thickness unknown. Unconformity. 2. Red shales with thin bands of blue limestone and yellowish calcareous sand- stone, about 300 feet. Lower Carboniferous fossils. 3. Massive blue limestone filled with crinoids and corals. Thickness unknown. Fossils collected from the red shales underlying the upper blue limestone unconformabh^ were determined by Dr. Girty to be Upper Carboniferous or Pennsylvanian, rather than Lower Carboniferous. Therefore the line between LTpper and Lower Carboniferous lies between 2 and 3. About half a mile south of Indian Creek, fossils collected by Mr. Rowe from the rocks that apparently underlie Ihe red beds from which the LTpper Carboniferous fossils were taken, were found by Dr. Girty to be Lower Carboniferons or Mississippian. About 7 miles south of Indian Creek, the fol'owing Carboniferous section was found by Mr. Rowe, overlying the Cambrian. The sec- tion is given from the toj:* down. Section 7 miles south of Indian Creek. 1. Massive dark-blue limestone, weathering rough, and containing white calcite spots. 2. Light-gray, massive, unfossiliferous limestone. 3. Massive dark-blue limestone, like No. 1. About 3 or 4 miles south of Hornet Spring fossils are found in yellow- weathering, blue, slialy, argillaceous, cherty limestone, which lies to the south of the thin-bedded Cambrian limestone, and is not readily separable from it in the field. In this yellowish, shaly limestone Fusidina cylindrica was found, and the liorizon was therefore deter- mined by Di". Girty as Upper Ca-boniferous. Southward from here, as far as the jDoint where the road enters the foothills, tlie ]"ocks are all similar thin-bedded limestones. To the east, Charleston Peak and the high ridge south of it are formed of massive limestone, which has all the appearance of belong- ing to the great Carboniferous series. Mr. Turner has informed the writer that Carboniferous fossils have actually been found on Charles- ton Peak by surveyors. On the east side of Charleston Canyon Mr. Rowe* noted that the range seemed to be made ux3 of Carboniferous limestone. Well down in these strata some fossils were found, chiefly Fusulina. The rocks are light-gray arenaceous limestones, containing considerabk^ chert. a Taken from Mr. Rowe's notebooks of 1900 and 1901, after his death, by the writer. b Notebooks. See above. 1G8 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. Fossils collected by Mr. Rowe were identified hy Dr. Girty as Peuu- sylvauian oi- Upper Carboniferous. la the foothills of the range, just east of White's ranch, in Pahrump Valley, a collection of Lower Carboniferous fossils was obtained, as determined by Dr. Girty: Zaphrentis sp. Spiriferina sp. Aulopora sp. Atliyris lamellosa. Fenestella sp. Seminula sp. Leptsena I'homboidalis. Rhynclionella sp. Chonetes planumbontis ? Beyricliia sp. Productus cf. mesialis. Phillipsia sp. Spirifer cf . grimesi. About 7 miles north of the above locality the rocks are also Carbon- iferous, according- to a note supplied b}^ Mr. Turner. Fossils were collected bj^ Mr. F. C. Boyce from near Fremont Wash, 7^ miles north-northeast of Manse post-office (White's ranch). On these Mr. Schuchert, of the United States National Museum, reported: The fossils * * * are of Carboniferous age. There are two species of Za- phrentis, a Syringopora near multaticnuata and a Spirifer fragment too small for determination. South of Manse the range was not visited by the writer, but he observed that the same series of rocks extended east and soutli for a number of miles. Mr. Gilbert, however, observed Carboniferous rocks east and south of here, at Cottonwood Spring^ and at Olcott Peak.^ At the first-named locality Mr. Gilbert made the following section: Section at Cottomcood Spring. Feet. 1. Massive red and yellow sandstone: a. Yellow, 250 feet 1 h. Red, 150 feet ". | „ c. Yellow, 200 feet ' ' II d. Red and shaly, 400 feet 2. Bedded, fine-grained to saccharoid limestone, gray and cream-colored: beds separated by shaly layers so as to weather in steps. [Phillipsia (?) , Macrocheihts (non des.), Naticopsis, Aviculopecten, Avicida, Meek- ella, Myalina, Productus semiretieulatiis, Spirifer lineatus, Athyris suhtilita, Synocladia] 500 S. Massive gypsum, white and red, in lenticular masses to 70 4. Gray, massive, cherty limestone: a. Jjivaestone [Meekella, Productus, CticeteteSjSyiHngojyora], 250 feet A b. Unseen; red (shale ?) , 25 feet. . _ : \ 475 c. Limestone, 200 feet . J 5. Friable sandstone, in places shaly or marly; variegated with brilliant iron colors 350 Total _. ^ 2,395 The fossils here show that the rocks of the section are Upper Car- boniferous. At Olcott Peak the fossils, according to Mr. Gilbert, are Lower Carboniferous. aU. S. Geog. Surv. W One Hundredth Mer., Vol. Ill, p. 166. 61bid., p. 32. SPURR.] SPRING MOUNTAIN RANGE. 169 At Mountain Spring, a point about G miles west of Cottonwood Spring, Mr. Gilbert" notes that Mr. C. A. Ogden obtained a set of fossils of facies older than the Coal Measures. Among the forms are PMUi2:)sia, 82:)irifer (two species of Devonian aspect), RhynchoneUa, Hemipronites, Afhyn's (distinct from A. suhtilita), Choneies, Tere- hratula (.^), Productus (like P. subacideatus), and FenesteUa. The horizon is referred to the Lower Carboniferous. The following valuable observations on the Carboniferous of the southern portion of the Spring Mountain Range were made bj^ Mr. R. B. Rowe in 1900-1901:* Lower Carboniferous. — About 6 miles south of Good Spring, Lower Carboniferous limestones are found, probably separated by an over- thrust fault from Mesozoic strata. The Carboniferous is much altered, but in some of the layers good corals are found. The Mesozoic beds consist of rich shales and sandstones. At Mountain Spring fossil-bearing Lower Carboniferous beds not more than 3,000 feet thick occur. Above these are Carboniferous red beds, at least 2,000 feet thick, which are overlain by Upper Carbon- iferous limestone, from 500 to 600 feet thick. Beneath the Lower Car- boniferous is a light-graj^ arenaceous limestone. The line between this limestone and the overljang Carboniferous limestone is sharply drawn. *" Carboniferous red beds {Upper Carboniferous). — About one-half mile west of Mountain Spring, on the road to Mule Spring, is a dark fossiliferous limestone lying upon a light-colored, much-altered lime- stone. These limestones are ijrobably Lower Carboniferous. In the vallej^ west of Mountain Spring they are overlain \)y a considerable thickness (2,000 feet?) of red Carboniferous shales and sandstones, which form a greater portion of the Mule Spring Mountains and are capped by the Upper Carboniferous fossil-bearing cherty limestones. On the east side of Mule Spring Mountain the red shales and sand- stones are found at the base, capped b}^ the Upper Carboniferous limestones. For 8 or 10 miles north and northwest of Mule Spring the Upper Carboniferous is overlain hy the fossiliferous Jurassic. '^^ There are no red beds or conglomerates between the two formations, although some of the topmost layers of the Carboniferous are conglomeratic. The thickness of the Upper Carboniferous limestone is about 500 feet. The thickness of the Upper Carboniferous red shales and sandstones exposed in this region must be two or three times as much. Between Mule Spring and Mountain Spring red sandstone occurs, with a northerly strike and a dip 20° west. At Mountain Spring the Carboniferous red beds lying above the all. S. Geog. Surv. W. One Hundredth Mer., Vol. HI., p. 180. 6 Taken from his notebooks, after his death, by the writer. c See citation from Mr. Gilbert on region of Mountain Spring, above. d Mr. Rowe's field determination. 170 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL. Lbull.308. Lower Carboniferous are at least 2,000 feet thick, and are overlain i by 500 to 600 feet of Upper Carboniferous limestone. On a divide along the road between Good Spring and Cottonwood Spring, Carboniferous red beds immediately underlie the fossilifer- ous Jurassic,'^ as is the case also at Good Spring; but about G miles east of Cottonwood Spring the Jurassic'^ lies directly upon the Upper j Carboniferous limestone. South of Indian Spring, at the northern end of the range, are red shales and sandstones underlying massive blue limestones uncon- formably. The shaly layers and the thin limestone bands in these red beds are fossiliferons. They were determined by Dr. Girty as Upper Carboniferous. The formation here has a thickness of about 300 feet. It overlies blue massive Lower Carboniferous lime- stone. U'pyer Carboniferous limestone.— For 8 or 10 miles north and noi'th- west of Mule Spring the folded Upper Carboniferous is overlain by fossiliferons Jurassic. " The Upper Carboniferous limestone is about 500 feet tliick ; the Upper Carboniferous red shales and sandstones about 2,000 feet thick. The Upper Carboniferous limestone maj^ be divided about equally into (1) upper clierty massive limestone, con- taining abundant fossils; (2) lower light-gray, massive limestone, containing a few fossils. The two portions are divided in some i^laces by layers of red shales and sandstones, as, for example, at Cotton- wood Spring. One-half mile west of Mule Spring Mr. Rowe col- lected fossils determined by Dr. Girtj^ as Pennsylvanian or LTpper Carboniferous. On the escarpment of the west side of the Mule Sj)ring Mountain there is exposed the Upper Carboniferous limestone, underlain by the red shale formation. At Mountain Spring, Cai'boniferous red beds are at least 2,000 feet thick. They overlie about 3,000 feet of Lower Carboniferous strata, and underlie Upper Carboniferous limestone from 500 to 600 feet thick. Beneath the Lower Carboniferous is a light-graj^ arenaceous limestone, containing no discovered fossils. At Cottonwood Spring fossils were collected from the Upper Car- boniferous by Mr. Rowe, and were subsequently identified as such by Dr. Girty.* Upper JCarboniferous beds were followed [some distance south of Cottonwood Spring ; also east of Cottonwood Spring. In the hills north and northwest of Cottonwood Spring the Upper Carboniferous is overlain by conglomerate and strongly cross-bedded coarse sandstone, in beds 10 or 20 feet thick. Above these conglom- erates are shales and gypsum beds, above which again are the fossil- iferous arenaceous Jurassic" limestones. a Mr. Rowe's field determination. ''See citation from Mr. Gilbert on Upper Carboniferous at Cottonwood Spring, above. ^ Mr. Rowe's field determination. SPURR] SPRING MOUNTAIN RANGE. 171 About 3 miles southeast of tlie summit, between Good Spring and A\"ilson's ranch, the Lower Carboniferous of the Bird Spiring Range lies against the Upper Carboniferous and Jurassic,'^ being separated l)y a fault. About 6 miles east of Cottonwood Spring, directly overlooking Las ^'egas Valley, is an escarpment consisting of Upper Carboniferous beds. These are underlain bj^ lieavj^ shales and brownish micaceous sandstone, much cross-bedded. At this point the red beds seen are not over 50 feet thick. Between Good Spring and Cottonwood Spring the Upper Carbon- iferous repeatedlj^ occurs. North of Good Spring a low knoll of the Upper Carboniferous occurs west of the road, up to the Mesozoic cliff at the foot of Oleott Peak (Potosi Mountain). Near the summit both Carboniferous and Mesozoic rocks occur along the road. East and north of Cottonwood Spring are apparentl}^ Carboniferous rocks, while south and west are Mesozoic. About 12 miles north of Good Spring, near the divide between Good Spring and Cottonwood Spring, is a small area of Upper Carbonifer- ous, occupying a fault zone which s^^arates the probably Mesozoic red sandstones and shales from the Lower Carboniferous limestones which make up Oleott Peak.* On the east side of Oleott Peak, about 10 miles north of Good Spring, fossils were collected by Mr. Rowe that were identified b}' Dr. Girty as Upper Carboniferous or Pennsylvanian . About 3 miles northeast of Good Spring, in the Bird Spring Moun- tains, there was noted about 425 feet of gray, brownish, and pinkish arenaceous limestone. Fossils collected at three different horizons in the series bj^ Mr. Rowe were determined by Dr. Girty to be Upper Carboniferous or Pennsylvanian. At Good Sj)ring the following section was obtained, from the top down : Section at Good Spring. Consolidated ancient tains 6-10 Arenaceous light-brown limestone, rather thin bedded 610 In part yellowish and reddish shales and sandstones, which make the same red terrane as shown at the eastern base of Oleott Peak 760 Heavy conglomerate, siibangular pebbles 50 Gray limestone with some red and pinkish arenaceous layers and cherty layers: the tipper 50 feet is conglomeratic and contains large qiiartzite bowlders: fossils abundant in the conglomerate, less so in the rest 300 Mr. Rowe regards the 50 feet of conglomerate underlying the red beds as a basal conglomerate, and the conglomerate at the top of the limestone beneath as an apical conglomerate. Fossils of the lower conglomerate collected by Mr. Rowe are regarded hx Dr. GiYij as probably Permian, or uppermost Carboniferous. Fossils collected « Mr. Rowe's field determination. &See citation from Mr. Gilbert on Lower Carboniferous at Oleott Peak, above. 172 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. from the arenaceous limestone overlying the red beds are regarded by Dr. T. W. Stanton as not younger than Trias, and perhaps as old as the Permian. Fossils collected from the Upper Carboniferous at Cottonwood Spring by Mr. Rowe are regarded as possibly Permian by Dr. Girt3^ East and southeast of Good Spring, along the road to Manvel, occurs the contact of the Mesozoic and Carboniferous. On the east and north are Upper Carboniferous beds with fossils identical with those found at Good Spring. The red shales, sandstones, and con- glomerates which He between the Upper Carboniferous and Jurassic at Good Spring and at Olcott Peak are wanting about 5 miles south- east of Good Spring, and the calcareous sandstones of the Jurassic lie directly upon the Carboniferous. The Upper Carboniferous also has lost at this point the conglomerate which lies at its top at Good Spring. The mountains near Good Spring are chiefly limestones, with con- siderable sandstone underlying. Fossils collected by Mr. Rowe from the lowest rocks exposed in the Bird Spring Range" were identified by Dr. Girty as Pennsylvanian. or Upper Carboniferous. Correlation ivith Grcmd Canyon section. — In the Grand Canj^on and Colorado Plateau region the Carboniferous was studied in the course of the Wheeler survey by Messrs. Gilbert and Marvine. It was divided into the Aubrey limestone, the Aubrey sandstones, and the Red Wall limestone. The Aubrey limestone has a maximum thickness of 820 feet, and contains fossils suggesting the Permo-Carboniferous of the Mississippi Vallej^, and indicating the close of the Carboniferous age. The limestone is characterized by a great abundance of chert, which toward the top sometimes constitutes half the mass. Near the middle it is in some places interrupted by a bed of shale with gypsum. The Aubrey sandstone has a thickness along the Grand Canyon of about 1,000 feet. A portion is massive and cross-bedded, another portion soft and gypsiferous. The sandstones contain no fossils, but an intercalated limestone bears Coal Measures shells. The Red Wall limestone has a gray color on fresh fracture. It is heavy-bedded and massive. Near the top sandstone alternates with the limestone for from 200 to 500 feet. Tiirough its lower half the limestone is interrupted by occasional shaly bands. The average total thickness is 2,500 feet. Fossils are abundant near the top, but in the lower portions are difficult to find. The lowest fossils were found a little below the middle of the series, and were doubtfully referred to the Lower Carboniferous. The fauna of the upper portion is rich, and, while different from that of the Aubrey limestone, is referable to the Coal Measures. Mr. Gilbert ^ was not able to exactly correlate the Colorado Plateau « The southern prolongation of the Spring Mountain Range, lying east of Good Spring. b U. S. Geog. Surv. W. One Hundredth Mer , Vol. Ill, pp. 177, 178, 179. SPURR.] SPRING MOUNTAIN RANGE. 173 and Grand Canyon Carboniferous witli the Carboniferous series in the Spring Mountain Range. Nevertlieless, the Carboniferous de- scribed by Mr. Rowe seems to bear a general resemblance to the Colorado Plateau and Grand Canj^on section. This correlation may be suggested : Correlation of Spring Mountai)i coid Grand Canyon sections. Gilbert and Marvine, Grand Canyon section. RoXve, Spring Mountain section. Aubrey limestone, maximum 830 feet, Upper Upper Carboniferous limestone, 500-600 feet. Carb'oniferoiis. Aubi'ey sandstone, l.(XXl feet, probably Upper Carboniferous red sandstone, shale, and con- Carboniferous, glomerate, 1,000-2,000 feet, probably Upper I Carboniferous. Red "Wall limestone, Upper and Lower Carbon- ' Lower Carboniferous limestones, 3,000 feet, iferous, 3,500 feet. [ MESOZOIC. Eight or 10 miles north and northwest of Mule Spring the Upper Carboniferous is overlain by fossiliferous Jurassic.^ Among the fos- sils seen in the Jurassic Pentacrinus astericus"' is very abundant. About 4 miles west of Cottonwood Spring is a great escarpment, at least 2,000 feet high. It consists of two terranes, the lower being red shales and sandstones, making up about one-third of the height. Above this is a heavj^ yellow sandstone, containing occasional red lenses. These rocks are probably Mesozoic. To the east and northeast of Cottonw^ood Spring the hills appear to be Mesozoic also. In the hills north and northwest of Cottonwood Spring the Upper Carboniferous is overlain by beds of conglomerate and coarse, strongly cross-bedded sandstone. These beds are from 10 to 20 feet thick. Overlying these conglomerates are 100 feet or more of intercalated white gj-psum beds and red shales, and above these lies the fossil- iferous arenaceous limestone of the Jurassic.'* Near the bottom of the fossiliferous beds is a stratum containing a multitude of Gryphoea/'' About 10 miles north of Wilson's ranch, the Carboniferous lime- stone has been brought above massive red Mesozoic sandstone by a great overthrust fault. Between Wilson's i-anch and Red Spring the Mesozoic is also found. About 8 or 10 miles north of Wilson's ranch the same overthrust fault as mentioned above was found. The mas- sive Mesozoic sandstone here is colored pink, bright vermilion red, and white. It is strongly cross bedded everywhere. Between Wilson's ranch and Cottonwood Si)ring the low hills show strata which contain Jurassic fossils. About three-quarters of a mile south of the summit, between Good Spring and Wilson's ranch, the Jurassic lies at the foot of a ridge made up of Upper Carboniferous rocks, the Carboniferous being sepa- rated from the Mesozoic by a fault. a Mr. Rowe's field determination. 174 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [btjll.308. At the foot of Olcott Peak there is a cliff composed of Mesozoic rocks. From here the Mesozoic turns east aud crosses the road before the summit between Good Spring and Cottonwood Spring is reached. Near the summit Carboniferous and Mesozoic alternate along the road. From the summit to Cottonwood Spring, Mesozoic rocks occur on both sides of the road. The rocks in the hills south and west of Cottonwood Spring are Mesozoic. On the great fault line which separates the Mesozoic from the Carboniferous between Good Spring and Cottonwood Spring, the fossiliferous Jurassic apparently lies beneath the red and white sand- stones which form the cliffs west of Wilson's ranch. At Good Spring the Mesozoic was found overlying the Carbonifer- ous. The following is the section : Section of Mesozoic at Good Spring. Feet. 1. Arenaceous limestone 610 2. At base yellowish and reddish sandstone about 50 feet thick. Above this are layers of red and yellowish shale. This may be the same red terrane which shows at the eastern base of Olcott Peak 760 3. Heavy conglomerate 50 4. Gray limestone, with some layers of red or pinkish arenaceoiis limestone, and abimdant layers of chert. The upper 50 feet contains numerous large quartzite bowlders . 300 Fossils collected from No. 1 were described, after a preliminary examination by Mr. T. W. Stanton, as belonging to a horizon not younger than the Triassic, and possibly as old as the Permian. The fossils collected from No. 4 were judged to be questionably Permian by Dr. Girty. East and southeast of Good Spring, along the road between Good Spring and Manvel, the road runs along the contact of the Mesozoic and the Carboniferous. The red shales, sandstones, and conglomer- ates which lie between the Upper Carboniferous and the Jurassic at Good Spring and Olcott Peak are wanting about 4 or 5 miles south- east of Good Spring, and the calcareous sandstones of the Jurassic lie directly upon the Carboniferous. About 6 miles south of Good Spring the Lower Carboniferous seems to be overthrust upon the Jurassic. IGNEOUS ROCKS. At Good Spring, near the southern end of the range, Mr. Gilbert '^ noted a flow of basalt. Other than this no igneous rock is known in the whole range. Mr. Rowe's notes record the following: At the Keystone mine, at the southern end of the range, there is an acid porphyry dike running N. 17° E. Along both sides of this, in a talcose material, gold is found. The dike dips from 35° to 40° W. aU. S. Geog. Siirv. W. One Hundredth Mer., Vol. III. SPURR.] SPRING MOUNTAIN RANGE. l75 East of Bird Spring Range, in the direction of the Colorado River, there appear to be extensive lava fields. STRUCTURE. The general observed strikes and dips of the strata in the Spring Mountain Range have been plotted by the writer from different points. The results show more complex folding than in any of the mountain ranges to the north and east, and to this folding the irregular shape of the range is probably due. In an east- west section the general structui-e of the range seems to be a broad syncline, with a number of minor folds, of little importance, and all part of the great fold. The axis of this syncline runs northeast and southwest, transverse to the general trend of the mountains and parallel to the axes of the folds in Las A^egas Range, already described, and well over to the western side of the mountains. Mr. Gilbert" gives a section of the Carbon- iferous rocks at Cottonwood Spring, Avhich shows the southeasterly side of this general syncline. At a point on the eastern face of the range, due southwest from Corn Creek in' Las Vegas Valle}^ a sharp, slight anticline, constitut- ing a wrinkle in the general syncline and with a parallel axis, may be observed. On the other side of the range a similar anticline runs along the foothills northward from White's ranch for some distance. It afterwards appears to pass into and occupj^the narrow north-south valley l^etween the northern end of the Spring Mountain Range and the low clusters of mountains immediately west. In a north-south section, however, the structure of the Spring Val- ley Range appears to be anticlinal, the strike at both the north and south end being in general east and west, and the dip varying up to 65° N. at the north end and up to about 20° S. at the south end. Taken altogether, therefore, the range exhibits a peculiar fold, anti- clinal in a north-south section, and showing a slightly complicated or wrinkled synclinorium in an east-west section. The portions of the center of the syncline that should lie flat dip north and south at each limb of the anticline. Except at the northern end the rocks of the range are chiefly Car- boniferous. At the northern end the Cambrian rocks are brought up, probably, by at least two heavy east-west faults. The northernmost of these faults observed lies north of Hornet Spring, and has appar- ently brought the Cambrian quartzite into juxtaposition with the Cambrian limestone, which stratigraphicall}^ overlies it. The throw of the fault must be at least 1,000 feet, and its course can be traced across the country by the break in the quartzite. The second fault lies 3 or 4 miles south of here, just south of Hornet Spring. It is probably parallel to the first, although it can not be traced so easily, L a\J. S. Geog. Surv. W. One Hundredth Mer., Vol. III. 176 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. « CS ^ ^ o 3 I ^ ^ 'S CD >^ CS •=3 ^ 'd -^ ';^ « CE "ce N SI o =« fi Oj ft S • .y CD O 1 cq .2 i:! & 6 N 0) >-{ +s pi f^ CO 4^ S aj o* ® fl fl.§ o C3 r-i a> l| P Pi as CS since it separates one limestone body from another. Bnt the lime- stone to the north is probably Mid- dle Cambrian, while to the south it is Upper Carboniferous. A ver- tical displacement of several thou- sand feet is here evidenced, the downthrow being to the south, as ■ is also the case with the first fault '■ mentioned. These two heavy faults have the same general direction as the heavy fault described in Las Ve- gas Range, and like it they have no primary effect on the topogra- phy, being marked by no scarps- (fig. 22). A third fault is suspected at the northern end of the range, sepa- rating the Carboniferous limestone from the supposedly Silurian lime- stone of the immediately adjacent! Desert Range. If this fault ex- ists, its downthrow is, like the others, to the south (fig. 22). The following important ol^ser- vations on structure have been; taken directly from Mr. Rowe's; notebooks, after the writing of the; above : About 10 miles west and north- west of Mule Spring, the Upper i Carboniferous is thrown into a se- ries of minor faults running in a nearly northwest direction, l^itch is very heavy toward south. These are probably southern ends of the folds uplifts which have brought up Charleston Peak. Together with the folding there was a great deal of minor faulting. A fault with a throw of a few hundred feet is seen about one-half mile west of Mule Spring. On the east side of Mule Spring is a steep escarpment The the the and 5PURK.] SPRING MOUNTAIN RANGE. 177 3omj)Osed of Uppei" Carbouiferous limestoues overlying red shales. [u this escarpiiieiit is shown a minor fault or a slight broken fold R^hich appears to be I'ecent and has directly displaced the surface. On the west side of Mule Spring, at Mule Spring Mountain, the same formations are shown in a similar escarpment. Here the beds are bhrown into minor folds and faults. A great fault runs in a northerly to northwesterly direction directly bhrough the center of the main Spring Mountain Range and through the minor ranges which are coutinous with it on the south (see map, PL I). This is shown 10 miles north of Wilson's ranch, where it funs nearly due north. It was also observed east of Mountain Spring (fig. 34), and at the east base of Olcott Peak (fig. 23), and was traced past Good Spring to the southeast. At Good Spring its course is north and south. Olcott Peai Fig. 23.— Section showing the great fault at Olcott Peak; after R. B. Rowe. 1. Lower Carboniferous limestones. 5. Mesozoic red beds. 3. Upper Carboniferous limestones. 6. Mesozoic heavy white sandstone. I Mountain Spring occupies the center of the important anticline which forms Olcott Peak or Potosi Mountain. East of Mountain Spring there is exposed the great fault. East of the fault is an ero- sion scarp (fig. 24). Between Wilson's ranch and Red Spring, and about 10 miles north of Wilson's ranch, there is an overthrust fault, by which the Carbonif- erous limestone is thrust over the massive red Mesozoic sandstone. Three important faults are shown here — two running parallel and nearly north or west, the other (the great fault) running at right angles, or nearly north and south. A,t Cottonwood Spring the apparent section is : Jurassic. Upper Carboniferous. Red Beds. Jurassic. Upper Carboniferous. This can only be explained by a fault. It is to be inferred that the fault is an overthrust. No direct evidence was seen. Bull. 208—03 12 178 GEOLOGY OF NEVADA SOUTH OF 40TH PAEALLEL. [bull.208. About 1 mile south of Cottonwood Spring the Carboniferous rocks strike S. 63° W., and dip 30° NW. About 6 miles east of Cotton- wood Spring a great escarpment consists of Upper Carboniferous beds underlain by reddish shales and sandstones. Mr. Rowe's sec- tion indicates that the escarpment has been formed by the erosion of these softer beds. In the valley east of the Cotton- wood Spring escarpment there is probably a fault within the shale belt. This must be an overthrust fault along bedding planes, because everything r.ppears to be conform- able. Red beds of the Carbonifer- ous overthrust on the red beds of the Mesozoic make the fault diffi- cult to see. Two or three days' search failed to reveal any direct indication (fig. 24). There is some minor faulting 'shown in the Upper Carboniferous strata about Cottonwood Spring, and some minor folding in the Ju- rassic east of the springs. On the divide between Good SiDring and Cottonwood Spring there appears to be some very sharp folding or faulting at right angles to the general trend of the great faults, and at right angles to the great fault running on the east side of the Charleston Range. The great fault lying on the east side of the Spring Mountain Range may be followed easily northward from Good Spring to the divide be- tween Good Spring and Cottonwood Spring, 12 miles. On the east side of the fault is heavy-bedded red sandstone and red shales. On the west is Middle or Lower Carbon- iferous and Upper Carboniferous pj ^ ►^ ft ^Cl mm m vMountain spring W- g CD tD Wilson rancli fc £? ^ , CottorrwoocL spring f/'roi?3b/y o^-ertfirust f3u/t or? bedd/rrg p/3f7ej Las Vegas "Valley SPURR.] SPRING MOUNTAIN EANGE. 179 wedged in the fault by tlie drag- (fig. 23). The section given bj^ Mi\ Rowe shows an anticline over- thrown to the east and faulted. The fold is cut deeply by canyons. Along its axis the rocks are much crushed and broken, and much minor faulting is visible in places. This great fault line was followed north toward AYilson's ranch. It changes its course from about 15° west of north, south of the summit, to 45° west of north, north of the summit. About o miles north of Good Spring the Carboniferous is folded into a sharp anticline and sj'ncline. The general structure of the Bird Spring Mountains seems to be anti- clinal, with a channel of erosion along the apex of the anticline. There is a fault along the east side of the range which brings the Lower Carboniferous against the red shales and sandstones of the Mesozoic. This fault runs uortliAvest and southeast (see fig. 25). About 14- miles north of Bird Sxjrings there is another fault, which crosses the first one at an angle and brings the Lower and Upper Carboniferous together. About 6 miles south of Good Spring the Lower Carboniferous is overthrust upon the Jurassic. The rocks are very much disturbed along the fault line. About three-quarters of a mile south of the summit, between Good Spring and Wilson's ranch, there is a fault which brings the Upper Carboniferous above the Jurassic. The fault has a nearly due north- west course. About 3 miles south- east of the summit there is another fault, also running due west, which B ^ 1\ m e g ^ 180 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. brings the Upper Carboniferous and Jurassic against the Lower Car- boniferous. These faults are nearly normal to the direction of the main northwest-running faults. Minor folds shown at the summit seem to be at right angles, or nearly so, to tlie main folds running northwest. About (3 or 7 miles west of Corn Creek, on the south side of the valley between Las Vegas Range and Spring Mountain Range, tliere is apparently a fault bringing the Cambrian against what is probably the Carboniferous.'' The Cambrian comprises a number of parallel ridges running east and west. The strata dip north. Each of the ridges has a steep escarpment facing south. Possibly there is a series of faults running parallel to the strike. Just south of Indian Spring, at the northern end of the range, the Upper Carboniferous limestones show considerable minor faulting and folding. Except where locally folded, the dip of these rocks is generally southwest. About one-half mile south of the spring, yel- lowish arenaceous limestone is brought by a fault against dark-blue cherty limestone. The rocks are much broken, also, bj^ minor faults, which are hard to observe. An unconformity is shown in several places between the red shaly Carboniferous beds and the overljang Carboniferous limestone. ORE DEPOSITS. In the extreme southern part of the range is the old Potosi or Yel- low Pine mining district. Here there are veins of argentiferous galena in the limestone.^ AREA SOUTH OF SPRING MOUNTAIN. From Mr. Rowe's notebooks the following information is taken : The range on. the east side of State Line Pass, about 12 miles soutli of Good Spring, shows fossiliferous Carboniferous limestone on the west side. The limestone on the east side is probably also Carbonif- erous, but no fossils were found. Tlie section made by Mr. Rowe seems to show faulting separating the two limestones. The beds dip throughout the whole section to the west. Mr. H. ^y. Turner has kindly supplied the following note: Locality on the boundary line between San Bernardino County, Nev., and Lincoln County, ISTev., at State Line Pass, at about G,000 feet elevation. Mr. Schuchert states that the collection wliicli was made by F. C. Boj^ce contains two sj)ecies — a CJucdetes, which is usually identified as C. milleporaceus Edwards and Ilaime, and a Productus of the P. cora type. The horizon from wliicli these fossils are derived is Carboniferous, and probably Upper Carboniferous. «This is very likely the same fault as described above by the writer (J. E. S.). &Geol. Surv. California, Vol. I, p. 471. SPURR.J KAWICH RANGE AND RALSTON DESERT. 181 The north end of the jNIeCnlloli Mountains is Carboniferous and seemed to be lithologieally like the Carboniferous of the Bird Spring- Mountains, consisting large!}' of light-gray arenaceous limestones. KAWICH RANGE. The Kawich Range forms the southern continuation of the Hot Creek Range, from which it is separated at its northern end onh' by a narrow transverse pass. From this point it extends due south about 60 miles, where its southern end runs out into the desert valley. TOPOGRAPHY. The range is high and is deeply eroded into bold, craggy mountains. On both sides the slope of the mountains is steep, es]3ecially on the west, where there are almost impassable cliffs. On the flanks of the range on both sides of the rugged backbone are smoother, mesa-like forms. SEDIMENTARY ROCKS. TERTIARY. The only stratified rocks known in the Kawich Range are the rhj'o- litic tuffs and sandstones which occur in the pass between the Kawich and the Hot Creek mountains and which also mantle around the north- ern base of the Kawich Range. These strata are evidently the same as those described at Twin Springs, between the Pancake and the Reveille ranges. They are closely associated with Tertiarj^ rhyolites. IGNEOUS ROCKS. The igneous rocks constitute the whole of the main range, so far as noted. The rough, deepl}' eroded central mass of the mountains is composed of biotite-rhyolite similar to the basal rhyolite of the Reveille Range. In these rhyolites, as in those of the Reveille Range, there is a pronounced north-south jointing or sheeting which is not found in the younger lavas. The dissected mesas found in a narrow belt at the base of the mountains are composed chiefly of more basic lavas, with some acid lavas. From the western side of the range, near its north- ern end, specimens of tordrillite and biotite-andesite were collected. In tlie pass between the Kawich and the Hot Creek niountains decom- posed andesite was found. At the northern end of the Kawich Range the rhj^olite abuts against the Paleozoic strata of the Hot Creek Range in such a way as to show that the mountains of the Hot Creek Range were already eroded out of the limestones before the rhyolites were extruded. RALSTON DESERT. East of the Sierra Nevada there is a belt of mountain ranges which have a Paleozoic or old granitic core, which have considerable heights, and whose general trend is northwest and southeast, parallel with the face of the Sierras. In this belt the rocks show frequently compressed or even overthrown folds, yet have experienced vastly less compres- 182 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. sion than the intensely folded and sheared strata of the Sierra. East of these auxiliary ranges there is a belt which is comparatively free from Paleozoic or old granitic ranges. It has been covered in many places by late Tertiary or Pleistocene lavas, so as partly to conceal the fact that it is a broad depression, but nevertheless this character is still traceable and even well marked on a topographic map. This great belt runs northwest and southeast, parallel with the Sierra, and separates the region of northwest-trending ranges on the west from the north-south trending ranges on the east. The Ralston Desert forms a portion of this. Northwest of the Ral- ston Desert the depression is continued by the lower end of Big Smoky Valley, by Sinkavata and Gabbs valleys, and farther north by the region of Carson and Pyramid lakes. Beyond this it appears to run up into Oregon. On the south the Ralston Desert is separated from the Amargosa Desert bj^ an irregular belt of late Tertiary volcanic mesas, through which Fortymile Canyon is cut. At the south end of the Amargosa Desert the open belt becomes narrow, but farther south passes into the Mohave Desert. The Ralston Desert is bounded on the north and south by late Tertiary volcanic mesas, which, indeed, are found throughout its ex- tent, so that these boundaries are rather arbitrarily taken. On the west the desert ends at the chiefly Paleozoic Silver Peak and Grape- vine ranges, while to the east it is limited chiefly by the rugged Kawicli Range, which apiDcars to be j)rincipall3^ rhyolite. In general the desert consists of an irregular but nearly level sandy plain, broken by bunches of low mesas or slightly eroded volcanic mountains. Stonewall Mountain, which lies about 30 miles east from Lida, is an exception to this topograph}^, being a high, rugged grouj), reaching probably 9,000 feet in altitude, or 4,000 feet above the desert at its base. The northern side of this mountain is a steep cliff: escarp- ment, probably 1,000 or 1,200 feet high, and is perhaps a simple fault- scarp. (See PI. VII, A.) ' IGNEOUS ROCKS. RHYOLITES. Stonewall Mountain is entirely made up of rhyolite, and has been so deeply eroded that it can not be of very recent age. This rock is probably the same as the rugged rhyolite core of the Kawich Range. Northeast of Stonewall the low mountains in which Cactus Corral is situated are composed of rhyolite and tordrillite, also considerably eroded and probably belonging to the same period. Most of the hills in the desert, however, show comparatively^ slight erosion. They represent thin flows, which have been very fluid and so have run comparatively long distances from the vent, at a very slight angle of descent. So the edges ai-e thin-benched mesas, while the thicker, inner i^arts are irregular hills. While these mesas are U. S. GEOLOGICAL SURVEY BULLETIN NO. 208 PL. VU A. NORTH SCARP OF STONEWALL MOUNTAIN. RALSTON DESERT. A fault scarp (?). B. PYRAMID PEAK, GRAPEVINE RANGE, FROM THE HEAD OF FURNACE CREEK. SPURR.] RALSTOjST desert AND LONE MOUNTAIN. 183 evidently younger than the deeply eroded rugged rhyolite of Stone- wall JMonntain, j'et they seem to be, in part at least, older than cer- tain horizontally stratified rhyolitic claj^s which will presently be described as occupying a large portion of the desert between the vol- canic hills and underlying the Pleistocene sands. Within these strati- fied clays, aud sometimes capping them, are also beds of rhyolite, very tine grained and often giassj'. This is evidently the youngest of all the rhyolites, and we may infer that the rhyolitic eruj)tions lasted a long time, beginning with those of Stonewall Mountain and ending with the slaggv flows last mentioned. The latest lava of the desert is a flow of slaggy olivine-basalt, hang at the base of Jackson Mountain, which is just east of Lida. This is not only vounger than the youngest rhyolite, but is apparently younger than the erosion of this and the underlying sediments to form the buttes, of which Jackson Mountain is one. SEDIMENTARY ROCKS. TERTIARY. The main portion of Jackson Mountain consists of several hundred feet of hardened, horizontal sands and clays, containing irregular fragmentri of rhyolite. The base of the mountain is at an elevation of 5,100 feet, so that the uppermost sediments are at least 0,000 feet. In the valley between Stonewall Springs and Cactus Corral there is also found green, hardened, rhyolite ash containing harder fragments. It is evenly and horizontally stratified and is overlain on the edges by the Pleistocene gulch dumps, or wash, which sometimes extend to the middle of the valle}^ The ash is eroded into hummocks. This thick series of volcanic sands and clays was probably depos- ited in a body of standing water and represents a lake contemporary with the later rhyolitic eruption. As seen from the sediment:; of Jack- son Mountain, the lake must have been at least 1,000 feet deep or the desert. PLEISTOCENE. Along the slopes of all the mountains, especially of Stonewall Moun- tain, are great wash slopes and gulch dumps fringing the scarp. This material, flowing down into the valle}^ overlies the Tertiary lake deposits. In the bottoms of the valleys are broad, bare mud flats or playas, evidently quite recent and contein]3oraueous with the gulch dumps. They seem to be simply sinks, where at intervals Avater col- lects and speedily evaporates. They do not represent the residuum of evaporated Pleistocene lakes of which, moreover, there is no other evidence. LONE MOUNTAIN. For the following slight description of Lone Mountain the writer is indebted to Mr. Turner, since he himself saw the mountain only from a distance. The mountain really forms the northern end of the ■ 184 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. Montezuma Ridge of the Silver Peak Range, but on account of its exceptional height and prominence has been given a separate name. IGNEOUS ROCKS. The main part of Lone Mountain consists of craggy, light-colored, massive granitic rock. SEDIMENTARY ROCKS. South of the granitic area the central portion consists of Cambrian limestone^ To the east of this Cambrian belt is a belt of Silui-ian limestones, as determined bj' Mr. Turner. Along tlie west flanks of the mountain the ujtturned beds of the Esmeralda formation (earlier Tertiary) occur. SILVER PEAK RANGE. The Silver Peak Range is short and somewhat irregular' in form. It lies immediately east of the northern end of the White Mountain Range, and like this range has a general northwest-southeast trend. On the north the range is separated by a Ioav pass from the Monte Cristo Mountains, while on the south it runs into the northern end of the Grapevine and Panamint ranges. From near the southern end of the range a spur runs off to the north, forming the eastern boun- dary of Clayton Valley, which lies between it and the main range. _ The Silver Peak Range was studied by Mr. H. W. Turner during || the summer of 1899, and the mapping of the formations over most of the range has been kindly furnished b}* Iiim to the writer. Most of the following notes on the geology, designed to explain the map, are also due to him. Mr. F. B. Weeks, of the Geological Survey, also spent some time during the same season in the Silver Peak region, chiefly for the purpose of collecting fossils, and the present writer passed through it on his wa}^ from Columbus to Lida. The range is mostly made uj) of folded Paleozoic rocks, together with intrusive granite and a large auionnt of volcanic material. SEDIMENTARY ROCKS. CAMBRIAN. Fossils obtained by Mr. J. K. Clayton, as early as 1866, at Silvei Peak, and fijst regarded as Silurian or Devonian, were shown by Mr. Walcott" to be Middle Cambrian. The studies of Mr. Turner have furnished many details concerning these Cambrian rocks, wliich occupy considerable portions of the range. In some of the Cam- brian limestones masses of the same corals occur as in the White Mountains to the west, so that Mr. Walcott regarded the two occur- rences as essentially forming part of a single reef. ^ The chief area of Cambrian is north of Silver Peak, where it is capped by volcanic rooks in many places. The buttes in Clayton a Bull. U. S. Geol. Siirvey No. 30, p. 38. ^ Am. Jour. Sci., 3cl series, Vol. XLIX , p. 144. SPURR.] SILVER PEAK RANGE. 185 Valley are also largely Cambviau. The section consists of comj)ara- 1 ively massive limestones and cxnartzites. Along the road leading from Silver Peak by way of Barrel Springs to the sontherii end of the range at Lida, the rocks are chiefly Cam- brian limestones. At Lida the writer collected fossils referred bv ]Mr. Yfalcott to the Lower Cambrian. Mr. Turner found overlying the Cambrian limestones other lime- stones containing occasional graptolites, which he therefore refers to the Sikirian. An area of these Silurian rocks occurs nortli of Benderes Pass, while a belt of the same rocks occurs encircling a granitic area north of Palmetto. Silurian rocks are also found on the southwest- ern edge of the branch mountain ridge above described, which ma}^ be called the "Montezuma Ridge" from the mining camp which is situated on it. EARLY TERTIARY. On the flanks of this range Mr. Turner has described sediments to which he gives the name of the Esmeralda formation.^' These dej)osits consist of sandstones, shales, volcanic tuffs, breccias, and conglom- erates, and great thicknesses of lacustral marls. Coal beds and plant remains occur; also fossil shells and fish bones. From this fossil evi- dence the age of the beds is broadly determined as late Eocene or early Miocene. The beds are nearly always folded, dipping from 10° to 40°, but the entire thickness may be several thousand feet. PLIOCENE. A butte in Clayton Valley, northeast from Silver Peak, which is capped In' olivine-basalt, is chieflj^ made up of horizontalh" stratified, partially' consolidated, green volcanic ash and tuff, with i^ebbles of dark hiva. The stratified beds are undoubtedly water- laid and are probably unconformable with the folded Tertiary series just described, which occurs in patches all over the valley to the north of here. In general appearance the beds are like the Pliocene sediments which have such a broad distribution north of here, such, for example, as occur on the pass between the Candelaria Mountains and the Pilot Mountains. They are also similar to the latter occurrence in being capped by olivine-basalt and not being folded. Going south from Silver Peak to Barrel Springs, the slopes of the mountains consist of rolled gravels whose pebbles are derived from most of the rocks around, including the lavas. These extend back eastward to the hills of the Montezuma Ridge, which are made up parti}' of volcanic rock. In the canyon below Barrel Springs the stratified gravels and sands, containing rhyolite pebbles, are found to lie against the eroded edge of a deposit of white volcanic ash and pumice apparently water-laid, and this ash lies against the eroded f Am. Geol., Vol. XXV, p. 168. 186 GEOLOGY OF NEVADA SOUTH OP 40TH PARALLEL, [bull.208. edge of the slightly dipiDing Cambrian limestone. These gravels and sands seem to be the same as those in the butte described above. In the outlying hills of the southern part of the range just east of Lida is a series of hardened, stratified, greenish clays and sands con- taining fragments of rhyolite. These clays have sometimes been eroded to form buttes, especially where capped by lava. They are horizontally stratified and undisturbed, and are younger than the flow of olivine-basalt which sometimes mantles around the base of the buttes. The deposits in these different localities may be provisionall}^ cor- related with the other sediments which have already been ascribed to the Pliocene-Pleistocene Shoshone Lake. IGNEOUS ROCKS. In the Silver Peak region the igneous rocks are abundant and varied. GRANITES. Granites occupy considerable areas, and field evidence shows that they are intrusive into the Paleozoic sediments, but not into the Tertiary rocks. VOLCANIC ROCKS. The volcanic history of the region is of considerable complexity and interest. Mr. Turner, who has made a study of this, has kindly supplied the writer with the information that the succession of lavas in this district has been, in general, (1) rhj^olites, (2) andesites, and (3) basalts. ORE DEPOSITS. At Silver Peak there are rich silver and gold mines. The Cam- brian limestones are cut by pegmatitic granitic rock, which changes to pegmatite and quartz veins. The ores appear to be, partly at least, connected with these intrusions. Numerous other localities are known where mineralization has occurred. At Barrel Springs the limestone is decomposed and stained along a vertical zone 10 yards wide with iron and copper. The honey- combed and cavernous appearance of the rocks shows that they have been the channel for ascending springs, to which the mineralization is undoubtedly due. At Lida the writer noticed an auriferous quartz vein 5 or 6 feet wide, occurring along the entire contact of a 20-foot-wide nearly vertical dike of quartz-monzonite-porphyry which cuts the nearlj^ horizontal Lower Cambrian limestones. This dike is evidently a phase of the general granitic intrusion and the quartz vein is an accompaniment. CHAPTER IV. GREAT BASIIvT RAISTGES OF CAIjIFOR^^IA, ?^0RTH OF MOHAVE DESERT. GRAPEVINE AND FUNERAL RANGES. The Grapevine and Funeral ranges are practically parts of a single mountain chain, which is the easternmost of the Important chains belonging to the Sierra Nevada auxiliary belt. This chain faces the Amargosa and the Ralston deserts on the east, and has a northwest- southeast trend. The Grapevine Range is continued on the north by the Silver Peak Range, from which it is separated only by a com- paratively narrow transverse valley. That portion of the range which lies immediately north of Furnace Creek has been sometimes called the Amargosa Range ; but in the present description all of the mountains from Furnace Creek north- ward will be included under the single term Grapevine Range, while those south of Furnace Creek will be described as the Funeral Mountains. To this southern portion of the range the name Amargosa has also been applied, and to certain parts of it the name Black Mountains; but these will here be omitted. The Funeral Mountains have a trend somewhat different from that of the Grapevine Range, being more nearly north and south. This change is accompanied by a similar change in the trend of the Pana- mint Range, which lies next west. The Grapevine Range is not of great width, but is high and narrow, with wild scenery (PI. VII, B). The Funeral Mountains are lower, and have a striking air of desolation, due to the lack of vegetation and the dai-k, gloomy colors of the rocks. Both the Grapevine and Fune- ral ranges are cut by deep canyons which sometimes extend quite through the range, a phenomenon frequent in the Great Basin ranges. At Furnace Creek the Grapevine Range fronts the Funeral Range with a south-facing scarp, so steep as to be almost inaccessible and about 4,000 or 5,000 feet in height. At the base of this scarp the drainage from it has cut a channel parallel with its^ front, which forms that branch of Furnace Creek along which the road runs across the mountains. Both the Grapevine and the Funeral mountains present steep sides to Death Valley, which are bolder than the western side of the valley, 187 188 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL. [bull-SOS. SEDIMENTARY ROCKS. Mr. George G. Davis has kindly sent the writer samples of the chief rocks at Gold Mountain, which ajtpear to be a grayish, rather coarse- grained quart2ate and a dark bliie-gi*ay slatj^ limestone of ancient appearance. These rocks may perhaps be Cambrian or Silurian. At Boundary Canj^on Mr. Gilbert found limestones with imperfect fossils, which, Avitli the stratigraphic data, serve to connect the rocks with the Cambrian beds observed farther east." At the extreme southern end of the range, at Saratoga Springs, Mr. Gilbert* has noted the following section (from toj) to bottom) : Section at Saratoga Springs. Feet. 1. Gray clay slate 600 2. Yellow slate, with beds of shaly limestone 800 3. Bedded and slialy limestone, banded in purple, yellow, and brown 350 4. Crystalline limestone . 40 5. Dark-brown qnartzose and argillaceous conglomerate 140 6. Crystalline limestone 85 7. Green shale 20 8. Massive hornblende rock, black to green 120 . Total 2,155 According to Mr. M. R. Campbell,'' the rocks composing the southern end of the Funeral Range at Saratoga Springs are limestone, shale, and quartzite, presumably of pre-Cambrian age and containing no fossils. They strike north and south, and dip about 50° E. No Ter- tiary rocks were seen in the southern end of the range from Saratoga Springs, while strata resembling those exposed at Saratoga Siorings could be traced nortliAvard for several miles into the high summits. SILURIAN. At Furnace Creek Valley the writer obsei'ved bowlders of pure white, vitreous quartzite extending down from P^a^amid Peak, although the main mass of the mountain is limestone. This quartzite resembles the Silurian Eureka quartzite, so persistent in Nevada, and the rela- tion of these beds to those overljing, which are probabty Devonian and Carboniferous, makes it probable that in Pja^amid Peak and west of it the strata are largely Silurian. The writer has been informed by Mr. F. B. Weeks, of the United States Geological Survey, that at Grapevine Peak limestones cariying Lower Silurian fossils (probabl.y corresponding to the Pogonip formation of Eureka) occur, and he regards these Silurian rocks as probablj^ continuous southward to Pyramid Peak. DEVONIAN. In the mountains east of Pyramid PeaK: a great series of easterly dipping limestones are exjDosed, in Avhich badly preserved fossils «U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, pp. 3S, 169, 181. 6Ibid.,p. 170. c Bull. U. S. Geological Survey No. aOO, 1903, p. 14. SPURR.] GKAPEVINE AND FUNERAL RANGES. 189 resembling those foiiiul in tlie rocks of the ranges just east of liere were observed. In the Kingston Range Devonian fossils were col- lected from similar rocks, and from the great thickness of the section exposed in the Grapevine Range at this point it is likely that both the Devonian and the Carboniferous may be represented here. TERTIARY. In the eastern part of the range, where the road crosses from the Amargosa Valley into Furnace Creek, there is found a great amount of conglomerate, forming high hills. These conglomerates are very coarse and contain rounded pebbles and bowlders of all sizes, made up of reddish and white quartzite and black and gray limestones bearing the badly preserved Paleozoic fossils above mentioned. The conglomerate is as hard and firm as the rocks from which it is derived. It is water-laid and well stratified, and evidently a shore formation. The whole thickness exx^osed is estimated at 4:,00() feet. It is sharply folded, together with the limestones from which it is derived, but it abuts abruptly against these limestones on the west. The irregularity of the contact between conglomerate and limesione denotes a great erosion interval, yet no unconformity of attitude is apparent. This conglomerate seems to fringe tlie north edge of the bold Paleozoic scarp of the Grapevine Mountains across the greater por- tion of the range. It is found at A^arious points. A little west of Pj'ramid Peak conglomerate occurs, interbedded with and running laterally into a hard limestone, which has all the appearance of being calcareous tufa. A specimen examined microscopically bears out this idea and shows that the rock is probabl}^ a chemical i)recipi- tate. It is like a rock found in crossing the Panamint Range from Death Valley to Windy Gaj:), and also like one from the Esmeralda formation, between the Candelaria Mountains and the Pilot Range. Besides these rocks there occur, as parts of the same series, semi- consolidated gi-avels, with clays j)artially hardened to slaty shales, limy clays partially consolidated to argillaceous secondary limestones, and sands partially hardened to cherty and limy sandstones, all interbedded. All these, including the conglomerate and the limestone tufa, have a general light-j^ellow, often greenish color, characteristic of the series. This sedimentary series makes up the greater i:)ortion of the Funeral Range. Along Furnace Creek Valley and on both sides of it the mountains consist chiefly of y^ellow-green strata capped by basalt. The lava seems to occur interbedded with the sedimentaries, as well as overlying them. The series is here consolidated into a hard clay rock, with occasional thin sandstone, and the general yellow-gi-een color is changed in places to reddish, j^ellowish, and i^inkish. The rocks are often gyj)siferous and contain abundant grass remains, 190 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. which are, however, indeterminable. From the yellow-green Tertiary series in the hills just east of the mouth of Furnace Creek there has been taken much borax, which occurs as borate of lime in beds in the strata. Superintendent Roach, of the borax works at Daggett, says that from one hill here — Mount Blanco — 200 tons of borax a day could be easily shii)ped. On the eastern side of -Death Valley, southward from Furnace Creek, the upturned yellow-green Tertiaries, with some few inter- calated sheets of lava, constitute the mountains. Beneath some of these sheets the clays are baked to a red, natural brick. The lavas seem to occur chiefly at the top of the j^ellow-green series, or at a still higher horizon, for the great mass of beds exposed in the lower por- tion of Furnace Creek contains no lava sheets; yet in these beds occur occasionally lava bowlders and pebbles, so that we conclude that the period was one of continual volcanic activity. From fragments of lava picked up at the base of the mountains and from observations at a distance tho lower lavas seem to be not so basic as the upper ones, which are chiefly olivine-basalt. A single specimen of biotite-andesite was all that was collected to represent these more siliceous volcanics. Near the summit of the pass, just east of Furnace Creek, there come in above the yellow-green Tertiary se)-ies softer, dark-brown, honeycombed conglomerates, recalling the similar rocks of Meadow Valley Canyon. Thin sheets of basalt are interbedded with the con- glomerates, but the great sheets lie on top. Patches of this same upper conglomerate series were elsewhere observed, and at one place its contact with the underlying yellow-green series appeared slightly discordant. The conglomerate contains pebbles and bowlders which i are chiefly of lava and must have been derived from the sheets of basalt which were periodically poured out during the deposition of [ the beds. A rough estimate of the thickness of this whole series of slightly consolidated beds and volcanics puts it at not less than 4,000 feet, , and the nature. of the sediments shows that they must have been i deposited in standing water. The presence in some of the beds of gypsum, borax, and calcareous tufa shows that at some jDcriods the waters in which the sediments were deposited were evaporated. They were, therefore, those of an inclosed lake, which was probably of great dimensions. It is likely that a large portion of the beds wei-e deposited in fresh water at a period different from that in which the chemical precipitates were laid down. The borax in these beds is probabl}^ contemporaneous with the borax deposits in similar folded Tertiaries at Daggett and elsewhere in the Mojave Desert. Between these two localities, moreover, the strata, so far as known, appear to be roughly continuous. The strata of Mojave Desert are exposed on a grand scale at Cajon Pass, where they contain beds of black lignite. SPURR.] GRAPEVINE AND FUNERAL RANGES. 191 Northward from Furnace Creek, at. Silver Peak, are found beds of the Esmerakla formation, which are eutirel}^ similar in nearly every respect to those at Furnace Creek. Moreover, the fossils found in the Esmeralda beds indicate a nearly similar age to that indicated by fossils found in the Tertiary strata of the Mojave Desert, just west of Cajon Pass. The upper part of the Furnace Creek beds is identical in appear- ance with certain semi-indurated and slightly folded conglomerates and sandstones found in Meadow Valley Canyon, which have been referred to the Pliocene.'* PLEISTOCENE. At the lower end of Furnace Creek the steeplj^ dipping Upper Tertiary gravels are overlain directly and unconformably by hori- zontal gravels, which are partly consolidated and form bluffs 15 feet high. These are the same gravels as were noted on the eastern flanks of the Panamint Range, on the road crossing to Windy Gap, the beds here having the same appearance and position. Their jjerfect hori- zontality indicates that they are perhaps the deposits of a post- Tertiary lake. This lake was a few hundred feet deep, as measured by tlie highest of these sediments. It therefore api^ears j)robable that the Furnace Creek beds repre- sent nearly the whole of the Tertiary period, from the Eocene through the Pliocene. It is jDossible also that the uppermost lavas belong in the Pleistocene, for they are fresh olivine-basalt, like that which is known to have been extruded throughout the Great Basin region during the Pleistocene.* A considerable portion of the area of greatest depression is occux)ied by a great brown desert. This has the api)earance of a newly jilowed field in color and form, and appears soft. On examination the surface is found to consist entirely of hard salt, rendered brown by a mixture of soil. This deposit is probably the result of the evai)oration of the Pleistocene lake. This lake was fed by the Amargosa River. The writer has been informed by those who are familiar with this region that occasionally^ the Amargosa River has been seen to be 200 feet wide at the southern end of Death Valley, although generally it is dry on the surface as far uj) as Ash Meadows. Along this dry course it flows underground, as is shown by the fact that water may. generally be found by digging a few feet below the surface. In Death Valley, also, water can be found in many places by digging, so the dregs of the lake may be said to still exist. "See description of Meadow Valley Canyon, Meadow Valley Range, Mormon Range, and Virgin Range. ''See J. E. Spurr, Succession and relation (jf lavas in the Great Basin region: Jour. Geol., Vol. VIII, p. 636. 192 GEOLOaY OF NEVADA SOUTH OF 40TH PARALLEL. [bull.x'OS. IC4NEOUS ROCKS. GRANULAR ROCKS. Granitic rocks are said to occur at Gold Mountain, at the northern end of the range, where the gold ores are connected with theni.'^ OLIVINE-BASALT AT FURNACE CREEK. The Funeral Mountains are capjjed by hea^'y flows of pyroxene- olivine-basalt, which seems to have been slightly involved in the latter part of the folding wliich affected the underlying Tertiaries. The rock is black and slaggy and is identical in appearance and composi- tion with the Pleistocene olivine-basalts found frequently in Nevada.* Besides capping the Tertiar}^ sediments, the basalt occurs in sheets which are, in part at least, certainly contemporaneous with the upper portion of the sediments, especially the conglomerate series. One basalt sheet was noted as metaniori^hosing the underlying conglomer- ates, but not the upper ones, and is therefore probably a flow and not an intruded sill. Moreover, the i)ebbles and bowlders in the ui3j)er conglomerate series are largely of the same basalt. ANDESITE AT FUkxj^cE CREEK. Beneath the basalt sheets there is a certain amount of less basic volcanic material in the beds. This was not carefully investigated, but a single specimen showed that biotite-andesite is represented. VOLCANICS NORTH OF FURNACE CREEK. North of Furnace Creek the Avholc northeastern side of the Grape-^ vine Range is overlapped by the sea of lava v\diich occurs over mostoi the Ralston and Amargosa deserts, except where obscured by Terti- arj^ or Pleistocene detrital accumulations. At the north end of the range these volcanics may connect with the volcanic area just north of Gold Mountain, which there extends to the western side of th( range and is probably connected with the lavas at the northern end of the Panamint Range. Mr. Gilbert'" notes that rhyolite occurs a few miles north of Boundary Canyon, flanking the range both on its eastern and its west-i ern side. STRUCTURE. Mr. Gilbert '^ has drawn a section of the Graj^evine Range at Bound- ary Canyon. This section shows essentially a main anticlinal fold, slightly overthroAvn to the west, Avith an auxiliar}^ broad anticline "Wheeler Survey Explorations in Nevada and Arizona, War Department, 1871, p. 47 I'J.E. Spnrr, Jour. Geol., Vol. VIII, p. 636. '•U. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 33. rflbid., p. 33. SPURK.] GRAPEVINE AND FUNERAL RANGES. 193 fonniiiii: the slopes of the vauiie towunl Death Valley, aiid a syncline between the two. These folds are much broken np l)y faults, which, as Mr. Gilbert notes, are not only longitudinal, but transverse." In crossing- the mountains at the junction of the Grajievine and Funeral ranges, on the road leading to Furnace Creek, a good struc- ture section was obtained. The south-facing scarp of the Grapevine Mountains shows a central chief anticline, with a very great thick- ness of uniformly easterly-dipping beds on the east limb. AVest from this central anticline, whose axis is immediately west of Pyramid Peak, there is a second anticline, also with steep dips, in the moun- tains immediately above Death Valley, and between the two anti- clines is a slight syncline. On the south side of the pass, in the lower Funeral Mountains, it seemed to the writer that there is about the same structure, although the dips ajjpear to be decidedly less. No faults were noted in this section, though the}' very likel}^ exist. The folds at Furnace Creek are probably continuous with those shown in Mr. Gilbert's section. As the writer looked along the face of the Grapevine Mountains, noi'thward from Furnace Creek, he thought to be able to trace the western anticline at least as far as Boundary Canyon. The Tertiary beds of the Funeral Mountains have therefore been folded together with the Paleozoics of the Grapevine Range. Yet the Paleozoic limestones appear to have in general steeper dips than the Tertiary strata. Nevertheless, the chief folding has come about since the deposition of the Tertiary. Not only the lower Tertiary beds, but also the upper conglomerates are folded, and even to a cer- tain extent the interbedded and overlying olivine-basalt, which is of fresh appearance and may be in part as young as Pleistocene. Cer- tainly, therefore, the upheaval of the Funeral Mountains and the present Grapevine Range has been very recent indeed. This is illustrated in the Funeral Range, which, as viewed by the writer, seemed to consist near its northern end of two anticlinal ridges with a synclinal valley between. This synclinal vallej^ is occupied by Furnace Creek, which follows the folding in all its bendings. The northwesterly course of the lower portion of Furnace Creek is caused by a corresponding bend in the synclinal trough. This deflection of the Furnace Creek syncline appears not to be continuous into the Paleozoic strata just north of here, and. it is very likely due to the differential folding of the Tertiary strata against the hard Paleozoic buttress. In the summit of the pass above Furnace Creek, this fold- ing against the Paleozoic cliff is well shown b}" a sharp local anticline in the Tertiary beds, the north limb of which dips from 20 degrees to 45 degrees toward the Paleozoic wall, which does not take part in the cMr. F. B. Weeks, of the U. S. Geological Survey, found in 1900 that at Grapevine Peak the main range was decidedly synclinal in structure, the axis of the fold in general transverse to the trend of the range. Bull. 208—03 13 194 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. flexure. This fold, however, is of slight width, the dip reversing and flattening a hundred yards south. (See PL VIII, A.) RESUME. The succession of events in the Grapevine and Funeral ranges and in the region of Death Valley is, then, about as follows: 1. Deposition of a thick, conformable. Paleozoic series. 2. Elevation to a land mass, without marked folding. 3. The formation of sharp, lofty mountains, with deep valleys. 4. The deposition of the thick Tertiary series. This took place, in part at least, in a great lake or inland sea. In this lake were deposited near the shores conglomerates and breccias derived from the Paleozoic rocks; in the other portions were formed silts mixed occasionally with gravels. During the deposition of this series, especially the later portion, there was volcanic activity, and sheets of lava were poured into the lake, thus becoming intercalated with the sedimentary beds. 5. The lake, probably generally fresh, was at certain times reduced and evaporated, so that beds containing salt, borax, silica, and lime were chemically precipitated and mingled with the detrital silts. 6. The volcanics changed to olivine-basalt. These lavas are asso- ciated with well-stratified sediments, such as might have been formed in a lake, but accurate data bearing on this point are lacking. The sediments may possibly be the result of stream action. They consist of brown and red conglomerates, which overlie the yellow-green lake beds, and are separated from them by some slight movement and per- haps an erosion gap. 7. Final flows of olivine-basalt. 8. Probably beginning before the deposition of the Tertiary, but not becoming very important until during and after the close of this period, came a disturbance, leading to rapid folding. The crvist was bent, and j)erhaps broken, forming hills and valleys. Death Valley was created. 9. The mountains were eroded, producing minor irregular forms. The climate being slightly moister than now, a shallow lake a few hundred feet deep was formed in the bottom of Death Valle3^ This soon became charged with salt, borax, etc., derived chiefly from the leaching of the earlier lake beds, now become mountains. At this period the late Pleistocene shore gravels were formed. 10. The climate becoming drier, the lake evaporated, leaving a salt desert. Since that time there has been only a slight incision of the lake shore conglomerate by the drainage from the mountains to the dry valley. AMARGOSA VALLEY. The Amargosa Valley lies between the Kingston and Funeral ranges. The following notes are from Mr. R. B. Howe's notebooks, except where credited to Mr. Campbell. "^ '"i N 1 M 1 m in 1) WM z < 1 ^ i m „ DC J 1 03 m < cr UJ z IS CD uWaXv! =3 tfli L fev® !- (0 in W\ v\v w - InH aOzrwmwp W " "(0 j[m )- if&aUQ 30rzru.jm.ffH _ '-^ ■* HllH. joiioruruff t- 1- nim r " > ^ ™ f-( ^ T3 C nJ N +' c ^ / y- i- " N I. 1 ">id P!'^e-"^d41r -in o 1 u"- - H 1 -4- - - - - 1 uJzV -}- M ^ rti " >0 1 -Hfl U^ ^3duj donyiMin^ "zf - J r--1 Ks||e/, H+^^a 4 ^ CO < '^' ^1 O il 3 :£-2 •^fi^ " E S _5 tr-j spuRR.l AMARGOSA VALLEY AND KINGSTON EANGE. 195 METAMORPHIC ROCKS. Metamorphic rocks are exposed about a mile below the China ranch. SEDIMENTARY ROCKS TERTIARY. Overlying the metamorphic rocks at the point mentioned above are Tertiary deposits. These Tertiary lakes were dry part of the time, or receded to a great extent and then swelled out again, for talus and lake deposits alternate with each other in the lower Amargosa. At China ranch the Amargosa River cuts through the Tertiary beds to a depth of 200 or 300 feet. Mr. M. R,. Campbell ^'' has indicated on a maj) two areas of Tertiary lake beds near Amargosa Valley, one around Resting Springs and the other south of Ash Meadow. STRUCTURE. At China ranch the Tertiaries have been uplifted so that they dip at a high angle. The structure seems to be monoclinal. There is also some faulting in the Tertiary beds. Above China ranch the late talus deposits overlying the Tertiary are tilted uj) to a high angle, together with the Tertiary rocks. For a distance of 3 miles, near China ranch, the Amargosa River has recently cut down about 20 feet into an old river deposit or wash. For a distance of about 1 mile it is beginning to cut down 4 or 5 feet farther. This is shown by waterfalls in the talus. This local down- cutting seems to indicate recent movement. Mr. M. R. Campbell* states that the Tertiary beds in this valley bear evidence of considerable crustal movement since their deposi- tion. The eastern margin that rests against the foot of the Kingston Range is 800 feet higher than the uppermost beds of the same series at the foot of Funeral Mountain. This indicates a depression toward the west, in the direction of Death Valley. It seems possible that the change was due to tlu^ sinking of Death Valley to its present position below sea level. KINGSTON RANGE. The Kingston Range lies between Pahrump Valley and the valley of Amargosa River. The Califoi-nia-Nevada line passes along its eastern base. Tlie range luis a northwest-southeast trend and is 50 or 60 miles in length. At its northern end it is separated by a short valley, called Stuart Valley, from the mountains which lie directly north of Pahrump Valley, and which form an irregular group afford- ing a partial connection between tlie Spring Mountain Rajige and the Kingston Range. This group will be described together with the Kingston Range. a Bulletin U. S. Geol. Survey No. m). f'Ibid., pp. 14, 15, 196 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. The Kingston Range generally has steep fronts, especially along the main eastern side, where it faces Palirnmp Valley. SEDIMENTARY ROCKS CAMBRIAN. Mr. R. B. Rowe, in 1900-1901, discovered and described Cambrian in the Kingston Range. The following information has been taken from his notebooks : The greater part of the Kingston Range is made up of Cambrian strata. On the road from the j)ost-office at Sand}^ to Kingston Peak there are sandstones and limestones, with metamorphosed gray schists cut by dikes. Kingston Mountain consists of a central core of granite, which is topped on tlie north and northeast by a fine-grained white quartzite with reddish bands. The succession at Kingston Peak, near Horse Spring, from the bottom up, is as follows: Section at Kingston Peak. 1. White, gray, or red qiiartzites. 2. Red, gray, and blue slates, and heavy beds i)f quartzite. 3. Dark blue, much altered limestone. 4. Light gray, arenaceous limestone, much altered, with crystallized calcite in its crevices and interspaces. 5. White and brownish quartzite, with conglomerate at the bottom. This sometimes alternates with the red, gray, and bine slates. In. some ijlaces the wliite quartzite at the base seems to run into a gray gneiss. On the road between Manse and Resting Springs, througli the pass going to Tecopa, there is an excellent section of the mountains east of Resting Springs. The Cambrian seems to be repeated at this point, probably by a fault. At Resting Si)rings the thickness of the Cam- brian, j)artly estimated and parti}' actually measured, is about 1,500 feet, and can not be more than 2,000 feet. About 4 or 5 miles north of Resting Si^rings the Cambrian is capped by lava. On the spur of the Kingston Range ending at Resting Springs, at a locality about 2 miles north of the springs, the following section, from the bottom up, was observed : Section £ miles north of Resting Springs. Feet. Heavy sandstone, probably all conglomeratic. Observed pebbles were all well-rounded quartzite 2, 000 Generally gray shales, with bands of sandstone 1 , 000 Dark-blue limestone with shales and siliceous limestones, containing trilo- bites and other Cambrian fossils 100 Quartzitic sandstones and shales 700 About 7 miles east of Resting Springs the rocks in the range, which is jjart of the Kingston Range, are in j)art Lower Cambrian, and are a -PUllIt. KINGSTON RANGE. ]97 repetition of those exposed at Resting Springs. There is shown in these mountains about 4,000 feet of Lower Cambrian or earlier rocks. Tliey consist chiefly of reddish and gray sandstone, some calcareous sandstones, and red and blue shales. Fossils were found within about 1,500 feet of the top, and none below that. Although a diligent search was made, they were found only in one ledge, and seemed to be poorly represented even there. About 800 feet below the top of the shale and sandstone formation, fossils are very abundant in some very thin sandstones. Thej^ consist mainly of trilobites, Hyolifhes, and a brachiopod. In the pass east of Resting Springs, about 800 feet beneath the dark blue limestones, Cambrian fossils were collected. The section consists, from. the bottom up, as follows: Section in 2'xifiii eafntral portion of these moun- tains is occupied hy a belt of granite, cutting obliquely across the range, with limestone on both sides. ORE DEPOSITS. Rich silver oi-es occur in these mountains, both in the limestone and granite. Farther south large deposits of coi^per are reported.^ PANAMINT RANGE. The Panamint Range is one of the most important of the ranges auxiliary to the Sierra Nevada, whicli lie in the belt east of it and run nj, E. S. '' U. S. Geog Snrv W. One Hundredth Mer. Vol. Ill, p. S:l. f Wlieeler Snrv. Expl. m Nevada and Arizona, War Department, 1S71, p. 53 SPURR.] PANAMINT RANGE. 201 northwest and sontheast parallel to its front. The range is abont 130 miles in length. At its northern end it merges into lava flows which unite it with the northern end of the Grapevine Range, while at its southern end it passes into low hills of Tertiaiy strata and associated lavas capped by later basic volcanics. It forms the southwestern barrier of Death Valley, which it fronts with a steep slope. This range has been verj" little explored and not much is known concerning its geology. The detail of its mapping, therefore, and especially the differentiation of the Paleozoic which is known to exist in its central i^ortion into the Cambrian and Silurian (as has been done on the accompanying map, PI. I), is very hypothetical. SEDIMENTARY ROCKS. CAMBRIAN. On the east front of the range, above the road from Furnace Creek in Death Valley to the crossing of the range at Windy Gap or Win- gate, a large portion of the range consists of older stratified rocks, which seem, as viewed from a distance, to lie beneath upturned Ter- tiary sediments and associated volcanics, and are cut through by masses of intrusive granite. No close examination of these older rocks was made, but the drift shows them to be in part finely crystal- line blue limestone, and in x)art quartzite, white, gray, or green, often considerably altered and often coarse grained. The amount of quart- zite in the drift implies a considerable thickness of this rock and suggests that the strata are of Cambrian age, as this is the onlj^ divi- sion of the Paleozoic in this region which contains great amounts of quartzite. From this neighborhood northward the Panamint Range is com- posed chiefly of old Paleozoic stratified rocks till near its northern end, as can be plainly seen from Death Vallej". On the accomi^anj^- ing map Cambrian rocks are represented as running along the crest of the range, the flanks being occupied by Silurian. The Panamint Range has been examined by Mr. II. W. Fairlianks'^ for some distance north of the region crossed b}^ the writer. Mr. Fairbanks found on the western side of the range, north of Windy Gap as far as the Pinto Range (whicli is a spur of the Panamint Range running northwesterly from the Wild Rose mining district), that a large portion of the rocks are mica- schists, quartzites, and marbles, which have been cut by intrusive granite. According to Mr. Fairbanks, the Pinto Range, as viewed from the Argus Range, appears also to be formed of bands of marble of various colors. In the Grapevine Range at Boundary Canyon Mr. Gilbert ^ f oiind limestones containing imperfect Cambrian fossils. lie notes that in that part of the Panamint Range which lies opposite Boundary Canyon the rocks appear from a distant view to be similar. "Notes on the geology of eastern California: Am. Geol., Vol. XVII, 1896, p. 63. 6U. S. Geog. Surv. W. One Hundredth Mer. , Vol. Ill, p. 33, 169, 181. 202 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull.208. The strike of the folds is parallel with the trend of the range, so that unless disturbed by cross faulting the same general formations will be found for many miles. Therefore the Cambrian and Silurian have been represented on the map as extending northward until covered by volcanic flows at the northern end of the range. SILURIAN AND CARBONIFEROUS. Mr. F. B. Weeks, of the U. S. Geological Survey, visited various parts of the range in 1900. Near Panamint he found quartzite and limestones which he referred on stratigraphic grounds to the Cam- brian. South of Shaw Peak (near the northern end of the range) he found a considerable extent of Silurian rocks, with Lower Silurian (Pogonip) fossils, as subsequently determined by Mr."Ulrich. South of here the Silurian Pogonip formation was succeeded by the over- lying Eureka quartzite, and still farther south were the Upper Silurian limestones, making the Silurian belt extend to Cottonwood Canyon. At the mouth of Cottonwood Canyon Mr. Weeks found Carboniferous fossils — Productus, crinoid stems, and a species of Serainula {?) . EARLY TERTIARY. The eastern flanks of the range fronting Death Valley, as seen on the road between Furnace Creek and Windy Gap, are composed of upturned, j^ellow-green strata and associated volcanics lying upon the older rocks with no evident unconformity, and partaking of their folds. This belt of interbedded volcanics and sediments grows wider toward the south, and soon completely covers, the Paleozoic area, which is wedged out between the younger series and the granite. The same series occurs along a great part of the road which crosses the range to Windy Gap. It consists of layers of calcareous tufa, evidently chemical deposits, with brown conglomerates containing lava bowlders, interstratified with and covered by lava, lava conglom- erate, and lava breccia. The lava in these belts proved, in three different samples, to be biotite-hornblende-andesite. This series of conglomerates, breccias, tufiis, chemical precipitates, and lavas is the same as that exposed on the ojDposite side of Death Valley, where it forms practically^ the whole mass of the Funeral Mountains. In the Funeral Mountains these rocks have been pro- visionally correlated with the Esmeralda formation in the Silver Peak Range, which are chiefly Eocene-Miocene. LATE TERTIARY. Mr. H. W. Fairbanks notes" that on the northern slopes of the Panamint Range, overlooking Mesquite Valley, there are large areas of gravels, which are unconsolidated and reach an elevation of 6,000 feet, extending nearly to the summit of the range. These may be aAm.GeoL.Vol. XVIl,1896,p.71. SPURR.] PANAMINT RANGE. 203 comparable to the j^onnger semi-iudurated conglomerate series in the Funeral Range, which is probablj^ late Tertiary/' or may be even Pleistocene. PLEISTOCENE, At the foot of the range, above Death Valley, at its southern end, one finds, overlying unconformably the Tertiary deposits just described, bluffs of well-rolled pebbles and small bowlders with per- fectly horizontal stratification, the strata making a continual angle with the slight dip of the surface to the east. This horizontalitj^ sug- gests that the deposit is a lake deposit, and connects it with similar conglomerates observed in a similar position in the lower part of Furnace Creek, in the Funeral Mountains. These conglomerates are also intimately connected with the gravels which occupy the bottom of Death Yalley and with the salt desert which occurs between the two localities just described. IGNEOUS ROCKS. In the southern portion of the range the core of the mountains for some distance is made up of a body of massive granite, which varies to g•ranite-porph5^r5^ This granite appears to be intrusive into the Paleozoic rocks, but not into the Tertiaries. Along the road which crosses the range east of Windy Gap the granite is hidden beneath these Tertiary rocks, but just south of the road another patch of granite is exposed around Granite Peak. The rock at Granite Peak was shown by microscopic examination to be a biotite-granite, verging toward alaskite, while farther north two samples of granite proved to be biotite-granite-porphyry. Farther north, according to Mr. Fairbanks,^ the granite which cuts the ancient limestones and quartzites in the mining regions on the east side of Panamint Vallej^ is a biotite-hornblende-granite with much quartz. VOLCANIC ROCKS. As already stated, volcanic rocks make up a considerable portion of the Tertiary formations. Three specimens of these rocks examined all proved to be biotite- or hornblende-andesite, but probably other rocks occur in the series. Overljang these folded lavas unconformably is a later flow of more basic rock, which covers a considerable area in the neighborhood of Browns Peak, just south of Windy Gap. Two specimens of this rock taken at different places proved to be in one ease pyroxene-aleutite, and in the other bronzite-olivine-aleutite.^ Analysis shows them to be rather siliceous for the species. aSee p. 191. &Ani. Geol., Vol. XVH, 1896, p. 72. cSee J. E. SpuiT, Am. Geol., Vol. XXV, p. 333. Aleutite is transitional between andesite and basalt. 204 GEOLOGY OF JSTEVADA SOUTH OF 40TH PARALLEL, [bull. 208. Mr. H. W. Fairbanks states'^' that ou the northern slopes of the Panamint Range, overlooking Mesquite Vallej^, there are scattered sheets of andesite and basalt. Yet another sei'ies of volcanics is exposed in this region. It is that forming the greater part of the Slate Range, which lies immediately west of the sonlhern end of the Panamint Range. The same rocks o^cur in the region south of Browns Peak, in the Panamint Range, underljdng the aleutites. These older volcanics are comparatively light colored and weathei' reddish ; they are, moreover, considerably sheared. Thin sections fail to exactly determine their nature, except that the}^ are really lavas with glassy groundmass, and that they are largely feldspathic. From the shearing it is jirobablethat these lavas are older than those in the folded Tertiar3^ series. Mr. Fairbanks^ found forming the highest portion of the Panamint Range for a number of miles east of Panamint a body of ancient rhyolite, which he regards as one of the most ancient lavas observed in the region. According to Mr. F. B. Weeks, of the United States Geological Sur- vey, who has visited the northern end of the Panamint Range, the Paleozoic rocks are here covered by extensive flows of lava, which appear to be nearlj^ continuous with the lava area at the extreme southwestern end of the Silver Peak Range. STRUCTURE. That portion of the Panamint Range between a point opposite Fur- nace Creek and Windy Gap api^eared to the writer, studjang it through field glasses, to be, in general, anticlinal. From Cottonwood Canyon northward to Shaw Peak, according to Mr. F. B. Weeks,^ the Pale- ozoic strata dip in general north of west. The Paleozoic and Tertiary strata on the east side of the range, south of Emigrant Canyon, are apparently conformable and have the same folds. There is here a series of alternating anticlines and syn- clines, having trends due north and south. Each of these folds maj^ be traced continuouslj^ for a number of miles. The axes of the folds, as sketched on the map, form a series of straight lines of moderate length, tiie more southern of which are continually^ offset to the east from the more northern ones. The explanation of this phenomenon may be a series of east-west faults, which fault the folds system- aticall}^ to the east on the south side. Just north of the eastern part of the road which runs from Furnace Creek to Windy Gap, where this road enters the Panamint Range, the strike of the folds changes from north and south to northwest and southeast, and so continues to the extreme termination of the range, in the neighborhood of Owlshead Peak. In all this extreme southern portion there are no Paleozoics, but the Tertiary interbedded sedi- « Letter to the writer. '' Am. Geol., Vol. XVII, 1896, p. 73. ''Oral communication. SPUHR.] LEACH POINT AND BURNT ROCK MOUNTAINS. 205 ments and lavas .show the same system of folding as in the Paleozoics, altlioiigh somewhat less pronouuced. The Pluto Mountains, a spur of the Panamiut Range, lying north- east of the "Wild Rose mining district, are stated by Mr. Fairbanks'* to have an apparent monoclinal structure, exposing an enormous thickness of strata whose truncated edges face Panamiut Yalley. In tlie Panamiut Range much of the deformation must be of com- paratively recent date. AVe know that much of it occurred since the deposition of the Tertiary beds and associated lavas, since these are involved with the Paleozoics in the upturning". ORE DEPOSITS. The following brief note on the ores of the Panamiut Range is gleaned from the reports of Mr. H. W. Fairbanks.* Near Postof&ce Springs gold is found in quartz veins inclosed in limestone, which is folded to a syncline, with slates below and on both sides. The ore is high grade. In the neighborhood of the old town of Panamiut are found silver-bearing sulphides of copper, antimony, and arsenic, sti'omeyerite and tetrahedrite being the most common minerals. The gangue of the veins is quartz, and the veins are found in all the sed- imentary formations of the district. North of here, in the Wild Rose district, a similar class of ores is found. Galena is seldom observed. LEACH POINT AND BURNT ROCK MOUNTAINS. The roughly defined east-west chain of low, irregular mountains which stretches eastward from the southern end of the Sierra Nevada at El Paso Peak to Pilot Knob is continued farther east in other Ioav, irregular mountains, which just east of Pilot Knob have been called the Burnt Rock Mountains, and still farther, in the same direction, the Leach Point Mountains. On the north of these mountaius the narrow Leach Point Yallej^ separates them from the southern end of the Pan- amiut Range. On the south lies the Mojave Desert. SEDIMENTARY ROCKS. LIMESTONE. About 8 miles northeast of Pilot Knob there occurs, along the main traveled road, an outlying spur from the low mountains, which is composed of very sandy blue limestone, amounting almost to a graj^ ciuartzite. This is interbedded with shaly and cherty thin- bedded limestones. This rock strikes N. 00° E. and dips E. 65°. It is slightly altered and sheared, and no fossils were found. It forms only a small patch, and is overlain by basalt. "Am. Geol., Vol. XVn, 1896, p. 66. & Mineral deposits of eastern California: Am. Geol., Vol. XVII, 1896, pp. 144, 151. 206 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull, 208. The bulk of the mountains Ijang east of Pilot Knob are flat topped and slightly pinnacled. They consist of light-colored stratified beds, with intercalated sheets of lava, the whole, in general, capped by black sheets of basalt. Mr. Gilbert '^ has also noted these deposits in this range. They are probably the sam^ as those exposed in the El Paso Mountains, where they contain Eocene fossils, and they are also the same as those which make up the Funeral Range and thus are widelj^ distributed throughout this region. IGNEOUS ROCKS. GRANITE. Along the western edge of these mountains granite is seen to be the basal rock. A specimen collected a few miles north of Pilot Knob appears to be a typical biotite-granite. The relation of this rock to the limestone above described is not known, but it is very likel}'^ intrusive in it, if we may judge from the similar occurrences in the Panamint and El Paso ranges and in other neighboring ranges. VOLCANIC ROCKS. Some miles north of Pilot Knob typical tordrillite* was collected, apparently derived from one of the sheets intercalated in the lake beds. Sheets of black basalt overlie the lake beds and constitute the latest volcanic rock of the region. STRUCTURE. The Tertiary beds and intercalated lava sheets seem to be, in gen- eral, nearly horizontal, but in one place at least — about 4 miles north- east of Pilot Knob — an anticlinal fold was observed, having a nearly north-south trend, with dips of from 10° to 20° on the limbs. WHITE MOUNTAIN RANGE. The important mountain range immediately east of the Sierra has gone by the name of the White Mountains in its northern portion and the Inyo Range in its southern. Inasmuch as the two so-called ranges are not in any way disconnected, but form a complete whole, they will be here, for the sake of convenience, described together under the head of the White Mountain Range, as suggested by Mr. Walcott.'^ The range extends in a northwesterly and southeasterly direction, from the Candelaria Mountains on the north to the neighborhood of Owens Lake on the south, passing at both ends into lower, irregular mountains of lava. No part of the range has been visited by the writer, aJJ. S. Geog. Surv. W. One Hundredth Mer., Vol. HI, p. 125. 6 Differing from rliyolite in the lack of essential ferromagnesian constituents. See J. E. Spurr: Am. Geol., Vol. XXV, 1900, p. 230. cAm. Jour. Sci., 3d series, Vol. XLIX, p. 169. SPURR.] WHITE MOUNTAIN RANGE. 207 and the following notes are entirely a compilation of observations, although now for the first time brought together. The observers include Messrs. Gilbert, Walcott, Turner, and Weeks, of the United States Geological Survej'', and Goodyear, Gabb, and other geologists of the geological survey of California. TOPOGRAPHY. As a rule the topography of the White Mountains is characterized by great relief, with deep canyons and high peaks. On the eastern side of the range there is an abrupt scarp for manj'^ miles, while the western slope, although generally steep, is on the average considerably gentler than the eastern. White Mountain Peak, which is at the northern end of the range, is of granite, and is a conspicuous land- mark for many miles. It stands exactly on the boundary between Nevada and California. SEDIMENTARY ROCKS. CAMBRIAN. Near the central portion of the range, or at the southern end of the White Mountains proper, Mr. Gilbert '^ early observed a series of quartzites and schists with a little limestone. The age of this series he did not determine. Later Mr. Walcott investigated it and found it to be Lower Cambrian. Mr. Walcott's chief studies were on the western side of the range. In several canyons to the east of Big Pine, namely, Waucobi, Black, and Silver canyons, Mr. Walcott* found the following section: Section east of Big Pine. Feet. 4. Upper arenaceous beds 200 3. Alternating limestones and shales 1,000 2. Siliceous slates and quartzites 2, 000 1. Siliceous limestones . 1, 700 Total 4,900 No fossils were found in the lower limestone, but in the lower silice- ous series are annelid trails and in places the heads of Olenellus, Avhile in the upper limestone are great quantities of Cambrian corals, of the same types as occur in the Silver Peak Range to the east. Mr. Walcott notes that this is the oldest Cambrian fauna known in the western portion of the United States. Northward from this locality Mr. Walcott found Cambrian rocks along the western face of the range, nearly to its northern end. On the eastern side of the range he found many of the low moun- tains lying northeast of Salinas Valley^ to be Cambrian, and also a all. S. Geog. Surv. W. One Hundredtli Mer., Vol. ni, p. 169. 6Am. Jour. Sci., 3d series, Vol. XLIX, 1895, pp. 141-144. c Personal communication to the writer. I 208 GEOLOGY 01' NEVADA SOUTH OF 40TH PAHALLEL. [bull.208. great part of the main White Mountain Range bordering the same valley on the west. At the latter locality Cambrian rocks are cut by great masses of intrusive granite. At the northern end of the range Cambrian rocks occur in considerable quantities on the eastern side, alternating with areas of granite which are intrusive into them." The rocks have here suffered considerable contact metamorphism bj^ the granite, the limestones being sometimes changed to dolomitic marbles. SILURIAN. Mr. Walcott* discovered a patch of rocks bearing Silurian (Trenton) fossils on the eastern side of the range, southeast from Big Pine, along the road leading from Waucobi Canyon. Mr. F. B. Weeks* found in 1900, near the head of Mazurka Canyon, rolled remains of crinoids and fragments of biyozoa which indicate that the rocks at this place are not older than Middle Ordovician, and may be somewhat younger. At the southern end of the range, in the vicinity of Cerro Gordo, Dr. O. Loew^' reports that the rocks are largely Silurian limestones containing great numbers of fossils, whose genera and species, how- ever, he does not record. These rocks, he notes, are cut into by intrusive masses of granitic rocks. CARBONIFEROUS. Mr. Walcott'^ records that Mr. Fairbanks, of the California Mining Bureau, discovered the characteristic Coal Measures fossil, F'usuliiia cyUndrica, in the southern end of the range east of Keeler. Also at the southern end of the range, just below the summit of Cerro Gordo Peak the follow^ing Carboniferous fossils were found by Mr. Weeks in 1900, and were determined by Dr. Girty: Rhipidomella ? sp. Aniplexus westi ? Prodtictiis fragments. Marginifera splendens ? TRIASSICi Just east of Cami) Independence Dr. Horn, of the California geo- logical survey, discovered a fossil in a series of slates with intercalated limestone beds, which was considered by Mr. Gabb' to be Triassic. According to Professor Whitney, these same slates extend north- ward from Bend City (just east of Camp Independence) for :25 miles. Yet this general region is delineated on the map accompanying this nPersonal communication to the writer by Mr. Turner and Mr. Weeks. ''Personal communication to the writer. '■Ann. Rept. U. S. Geol. Surv. W. One Hundredth Mer., 1876, p. 63. ''Am. Jour. Sci., 3d series, Vol. XLIX, 1895, p. 144. Jonr. Geol., Vol. V, p. 340. i^ Ibid., p. 345. Bull. 208—03 1-1 210 GEOLOGY OF NEVADA SOUTH OF 40TH PARALLEL, [bull. 208. King." In the region just nortli of Lake Mono he found the highest deiDOsits of this lake at an altitude of 7,100 feet, and came to the con- clusion that the uppermost deposits of the ancient Lake Mono formed part of the deposits of the same great water body. When the great lake stood at this altitude it must have been connected by numerous straits with the valley of the present Owens River, which formed an arm of the same lake. The uppermost limit of the lake beds noted by Mr. Walcott coincides almost exactly with the uppermost limit in the vicinity of Lake Mono and to the north of it. It is therefore likely that the deposits on the slopes of the White Mountain Range are to be correlated with these other deposits. The age indicated by the fossils found by Mr. Walcott also coincides with the other determina- tions made in other localities, all combining to indicate a period between late Pliocene and early Pleistocene. If this is the case, no local elevation of the Wliite Mountains can be inferred from the position of the lake beds at the comparatively great altitude where they are found, since the altitude is similar over the whole region. As was inferred by the writer with reference to the region around Lake Mono, there appears to have been a general uplift of mountain and valley throughout this whole region, lifting the deposits of the Pliocene lake about 1,000 feet higher than farther north. South of Owens Lake Mr. Turner found * well-stratified sands, gravels, and tuffs, occupying a large portion of the valley beneath the overlying Pleistocene accumulations, and having a slight dip west- ward. These may belong to the same series as above described. The same beds are mentioned by Mr. Fairbanks,'^ who notes that at Owens Lake they reach an elevation of- at least 1,500 feet above the lake surface. Mr. Fairbanks regards these beds as formed under water. '^ IGNEOUS ROCKS. GRANITIC ROOKS. Mr. Gilbert ^ noted that the eastern ridge of the White Mountains, east of Deep Springs Valley, is composed of granite. The map of the California State Mining Bureau-^ shows a number of other granite areas. On this map the whole northern end of the range in the vicin- ity of White Mountain Peak is shown to be of granite, and also most of the range from Loehr Peak southward to Deep Springs Valley. Farther south, a considerable area of granitic rocks is shown south of a See pp. 117, 119, 1S3. & Personal comrmmication. (■Am. GeoL, Vol. XVII, p. 69. f'Mr. M. B. Campbell's later notes on these gravels (Bull. U. S. Geol. Survey No. 200, p. 20) show that they are gently folded lake sediments containing much volcanic tuff. They are very likely pre-Pliocene (Eocene or Miocene), like the lake beds in Funei-al Range. eV. S. Geog. Surv. W. One Hundredth Mer., Vol. Ill, p. 315. /Preliminary mineralogical and geological map of the State of California, 1891. SPURR] WHITE MOUNTAIISr RANGE. 211 Waucoln Peak,*^ while a small area is shown southwest of Salinas Val- lej^, also in the center of the range. In the low monntains lying northeast of Salinas Valley two considerable areas are shown. From personal commnnications of Messrs. Walcott, Turner, and Weeks, further information on the extent of the granite has been obtained. The two northern granite areas represented as separate on the above-cited map appear to be continuous between Loehr Peak and White Mountain Peak. On the eastern side of the northern end of the range a great deal of granitic rock is found, cutting bhe Cambrian sediments. Farther south, the granite area south of Waucobi Peak extends sontheastward in a continuous belt to the area southwest of Salinas Valley, and the Cambrian beds west of Salinas Valley are cut through by juasses of the same rock. VOLCANIC ROCKS. As noted above, many of the Triassic rocks are lavas. There are, moreover, some areas of Tertiary and Pleistocene lavas^ as repre- sented on the map. Mr. Gilbert ^ noted some basalt just east of Big Pine. The map of the California Mining Bureau, above mentioned, shows an area of volcanic rocks lying on the west flanks of the range in the neighborhood of Waucobi Peak, and connecting westward across Owens Vallej^ with a larger area of lava on the eastern, slopes of the Sierra. The same map also shows volcanic rocks lying on the northern slopes of the granite of White Mountain Peak, at the north- ern end of the range, and shows a great area of lava lying southeast of Owens Lake, and forming the southern end of the range. Mr. Turner found that the mountains east of Sandy Springs, which form a kind of connection between the northern end of the White Mountain Range and the Silver Peak Range, are mostly volcanic. ORE DEPOSITS. The following notes are taken from Mr. H. W. Fairbanks's writings. ^ Silver-lead ores, chiefly in limestone, are found about Cerro Gordo and southeast of Independence. Auriferous quartz veins are abundant. They are found north of Cerro Gordo, in the Beveridge district, in the Alhambra Hills, 5 miles north of Lone Pine, between Independence and Big Pine, and east and northeast of Bishop Creek. The veins are chiefly in or near granite, often at or near the contact of it with slates or limestones. They probablj^ have a genetic connection with the granitic intrusion. Subject series B, Descriptive geology, 27. U. S. Geological survey. Bulletins. I no. 208. Spurr, J, E. Descriptive geology of Nevada °^ south of the fortieth parallel and adjacent por- tions of California. 1903. ^ U. S. Dept. of the Interior. £ see also I U. S. Geological survey. Bull. 208—03 16 %r-' 1^ '-mx IP .."•■ ,,^^-^^.: I'.JCOJ.DCICAJ. UKCO.V.VAISSANIK M.\l' .VKXAMA SOITII Ol'- Till': |.()"' 1 'AHA l,I,H Ij Al J.rAI ■1':NT ( Al.lFOK'XIA □ ^ nu ■;^iif:^:rsss^::M BOSTON COLLEGE 3 9031 026 22809 8 fVW-