S. & I" BANCROFT LIBRARY THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA BANCROFT LIBRARY REPORT ON THE GEOLOGICAL EXCURSION THROUGH NEW MEXICO, ARIZONA, AND UTAH SUMMER OF 1906 BY DOUGLAS WILSON JOHNSON. [Reprinted from TECHNOLOGY QUARTERLY, Vol.- XIX, No. 4, December, 1906] 408 Report on tJie Geological Excursion CONTRIBUTION FROM THE DEPARTMENT OF GEOLOGY REPORT ON THE GEOLOGICAL EXCURSION THROUGH NEW MEXICO, ARIZONA, AND UTAH, SUMMER OF 1906 BY DOUGLAS WILSON JOHNSON IN connection with the study of certain problems in physiographic ^f geology, and for the purpose of supplying certain deficiencies in our teaching collection in that subject, I some time ago formulated the plans for a wagon trip through some of the more inaccessible parts of the Southwest. It seemed to me that such a trip would make possible Q the collection of data which might solve, or at least make desirable trt contributions to, some of the problems in connection with the history <; of the plateau province of Arizona and Utah, the origin of the volcanic 25 buttes in the 'Mount Taylor district, New Mexico, and the character jg and origin of the Basin Ranges of Utah ; also the collection of valuable . illustrative material for the courses in topographic, lithologic, and pale- Z ontologic geology. The execution of the plans for such an excursion 3E was made possible last spring by an award of $250 from the Austin *^ Fund, a grant of similar amount from the Sturgis-Hooper Fund of ^ Harvard University, and by private gifts from friends of the Institute amounting to $500. Dr. H. W. Shinier, of the Institute Geological Department, and Mr. C. H. Decker, a graduate of the Columbia University School of Mines, looked after the stratigraphic and economic geological problems more particularly, Dr. Shimer securing much material which will add greatly to the value of the Institute's teaching collections, and which will form the basis of future publications. The main energies of the party, however, were directed to the study of problems and the collection of material which were related to physiographic geology. The party left Albuquerque, central New Mexico, on the 3ist day of May, with camp outfit and provisions for a ten days' trip in the (o Douglas Wilson Johnson 409 Mount Taylor district. This region was made classic by the report of Major C. E. Button on the volcanic necks and other volcanic fea- tures there represented. These necks were described as showing vertical columnar structure in many cases, being of enormous size and nearly cylindrical in shape or somewhat elongated in one direction, while the adjacent sedimentary beds were not much disturbed. In recent years some doubt had been expressed as to the interpretation of these features, it being argued that vertical columnar structure should not be expected as a prominent feature in volcanic necks, but was rather indicative of some other origin for the famous buttes ; that it was difficult to understand how a cylindrical neck or plug could be forced up through sedimentary beds, especially if those beds were not profoundly disturbed. Professor Jaggar has concluded that -the Mato Tepee, or Devil's Tower, of Wyoming (fully described in his report on the geology of the Black Hills), a butte which bears a striking resem- blance to some of the New Mexico types, must be the remnant of an old laccolith, basing his conclusion on the vertical columnar structure, the undisturbed sediments at the base of the tower, and the association of the butte with undoubted laccoliths still well preserved. It was in the hope of securing data bearing on. this problem that we examined a number of the finest examples of the buttes in the Mount Taylor district. The study led to the following conclusions : (1) The buttes are undoubted volcanic necks of large size, one of them rising over 2,000 feet above the surrounding valley lowland. (2) Many of them show good columnar structure more or less nearly vertical ; it is believed that this position is due to the floor of the crater's acting as the cooling surface for the upper portion of the neck, at least, rather than the probably heated walls of the conduit up through which the lava came ; the columns developing at right angles to the cooling surface would thus be vertical, instead of radial or irreg- ular, as formerly supposed. (3) The necks are more or less cylindrical in shape, and have come up from unknown depths without in the least disturbing the surrounding sediments in most cases, thus showing that enormous plugs may force a clean passage through sedimentary rocks, however difficult the process may be of explanation (4) The age of the rocks, the general geology and physiography of the region, and the detailed character of the necks were studied. Typical rock specimens, fossils, and photographic views were obtained. The results of this study will be published during the year under the title, " The Volcanic Necks of the Mount Taylor Region, New Mexico." 4IO Report on the Geological Excursion After returning to Albuquerque, our party went by rail to the Big Bug mining district, some twenty-five miles southeast of Prescott, Arizona, where we made our headquarters in the northern end of the Bradshaw Mountains while outfitting for the trip across the deserts to the north. We experienced considerable difficulty in securing suit- able horses and wagons, but after some delay procured an outfit of five horses, two wagons, the necessary saddles, tent, bedding, provisions, etc., and on the iQth of June started northward. We soon turned eastward to the valley of the Verde River, making a study of the large limestone series of that district with a view to determining its age and origin. Thence turning northeast we followed up Oak Creek to the foot of the great Mogollon escarpment, which terminates the plateau district on the south, and after a few miles of the steepest and roughest road encountered during the whole summer reached the summit, where we could look far to the northward and see the San Francisco Mountain rising high above the surrounding forest-covered plateau surface, while below us to the south lay the arid lands of the basin region. Here we were able to trace the relations of several great faults which help to determine the rectangular pattern of the southern margin of the plateau in this region. Continuing northward to Flagstaff, we found extensive lava flows covering portions of the plateau which do not appear on the previous maps of the region. From Flagstaff we turned southeast to Walnut Canyon, the region of some of the best cliff-dwellings in the Southwest. Dr. Shimer made a detailed study of the geological section exposed in the canyon walls, collecting a series of characteristic fossils and determining the char- acter of the beds which weather into overhanging ledges and thus afford the conditions utilized by the cliff-dwellers in making their homes. We next passed around the western base of the San Francisco Mountain, and established a camp well up the northwest slope. From this camp we made a two days' trip with pack outfit to the summit of the old volcano to study the effect of ancient glaciation at the high- est levels. Although so far south, the peak rises to such an altitude (12,794 feet above sea level) that its summit was occupied by a local glacier during the glacial period, this glacier eroding a splendid cirque in the very centre of the volcano, and leaving a prominent terminal moraine a short distance down the valley into which the cirque opens. Even today the snows lie on the higher levels and in sheltered places Douglas Wilson Johnson 411 until well into the summer, our camp on the night of July 6 being pitched between two snowdrifts over 10 feet high. Five days later we were in the bottom of the Grand Canyon, 10,000 feet lower, our party almost prostrated by the intense heat. From the San Francisco volcano we went to a point near Grand View on the rim of the Grand Canyon of the Colorado, where we established a camp for several days. After visiting several points on the rim of the canyon, we descended the old abandoned Red Canyon trail, spending two nights and parts of three days in the Grand Can- yon, returning to the summit of the plateau by the Grand View trail. We then returned to the northern side of the San Francisco group, where we investigated a recent cinder cone and lava flow, so recent, in fact, that erosion has as yet produced no effect on either cone or flow, both being perfectly formed, dense black in color, and fairly free from soil or vegetation. Studies were made also of numerous other cones and flows throughout the plateau region, resulting in the estab- lishment of the fact that the so-called "period of basalt outflow" is really divisible into at least five or six different periods, with long ero- sion intervals between them. Collections of fossils and rock specimens from the Grand Canyon and other parts of this district were made. Crossing eastward to the Little Colorado River, and then northward to the trading post at Tuba, we secured our last supply of grain and provisions before entering on the most strenuous part of our journey, the crossing of the Painted Desert. Already we had suffered some difficulty in securing water fit to drink and sufficient grass for the horses. At Tuba we were disappointed to find no grain, except a little Indian corn, which the horses did not seem to regard with favor. With little prospect of grass on the desert, the outlook was discouraging. The weather was now intensely hot, so that we found it advisable to travel mainly at night, resting during the day. Accordingly we usually arose about three or four in the morning, drove until the heat became oppressive, rested until six in the evening, then drove until well into the night, or until we lost our way in the darkness. During the middle of the day we erected a canvas awning to protect ourselves from the sun, but even in the shade thus afforded our thermometer registered 115 and we found it difficult to sleep. We secured good water at Willow Springs, a short distance from Tuba, and began the journey northward along the western base of the Echo Cliffs. These cliffs are produced by erosion on an eastward 412 Report on the Geological Excursion dipping monocline of sandstone, but have a much sharper form and steeper back slope than would appear normal for the gentle monoclinal dip. This sharpness of form had been noted by Professor Davis, of Harvard University, on an excursion some years before, and tentatively ascribed to possible faulting along the back slope of the monocline. Several traverses across the monocline at critical points showed the absence of any such faults, but revealed the fact that cross bedding at high angles and with rather uniform eastward dip caused the rocks to weather with steep eastward slopes, thus determining the peculiar topographic feature observed in the cliffs. Numerous landslides on a large scale were observed, thus confirming the previous observations of Professor Davis regarding the recent revival of erosion in the Grand Canyon region, with consequent undermining of previously graded slopes, causing extensive landslides in the areas near the revived streams. By the time we reached the crossing of the Colorado River at Lee's Ferry, near the Utah line, our horses were pretty well exhausted, owing to the hot weather, lack of grain, sandy roads, and scarcity of grass, good grass being found at only two points along the road from Tuba. At Lee's Ferry we had counted on obtaining grain, but were greatly chagrined to find that the supply on hand at that point had been nearly consumed, so that the best we could do was to secure twenty-five pounds of oats, this to last five horses for over one hundred miles of desert and mountain roads ! Ten miles beyond the ferry we found ourselves facing a serious problem. The horses first stumbled repeatedly, then stopped short and refused to go another step. There was no grass, and it required a hunt of several hours to find a little pool of salty water and get the horses to it, after having first taken them out of the harness and let them rest. That evening we succeeded in getting them a little farther, but found no grass or water. The next morning we managed to reach good water and a little grass. Here it became necessary to leave one horse and one of the wagons behind and pull the other wagon by means of four horses. Walking ourselves, we were thus able to make about twelve miles, over very sandy roads and under an intensely hot sun. Returning with the horses the second day, the other horse and wagon were brought up, this method being persisted in until the foot of the Kaibab plateau on the western side of the desert was reached, an average advance of about six miles a day being made. After a short rest at a spring at the foot of the Kaibab, the horses were able to Douglas Wilson JoJmson 413 pull the wagons, one at a time, up to the higher country on the summit, where we found better grass. The Kaibab plateau and the Kanab desert were crossed with less difficulty, although the long delay had so far exhausted our own store of provisions that the members of the party had to get along with scanty rations the last four days before reaching a new base of supplies. In spite of the difficulties encountered this part of the trip was most profitable. We were able to make a study of the streams which are dissecting the east Kaibab monocline, and to discover marked dif- ferences between the lower and upper courses of the streams, indicating two distinct erosion periods in the development of the region. This conclusion was confirmed by the study of certain terraces discovered farther south along the monocline and by a consideration of the rela- tion of one of the larger valleys to the monocline, all of which features offer strong evidence in favor of the recently proposed theory that the faults and folds of the plateau province are much older than the present Colorado River, as opposed to the former belief that the river's course was first established and that the faults and folds are of later development. From Kanab, in southern Utah, our party went north to Upper Kanab to study the terraces which terminate the high plateaus on the south. The Tertiary beds, forming the highest part of this series, have been considered of lacustrine origin until late years, when the possibility of a subaerial origin has been entertained by some observers. We secured evidence, both here and farther north, strongly indicating a subaerial origin. The origin of the Triassic and Jurassic beds are also in doubt, and we made some studies as to detailed structures which we hope will aid in solving this problem. Collections of the rather scarce Jurassic fossils were made, and some points of interest regarding lava flows in the valleys noted. Returning to Kanab, we then went southward across the Uinkaret desert to the lower portion of the Toroweap valley near the Grand Canyon. This region was of special interest, as offering undoubted evidence as to the age of two of the great faults of the plateau province. The region being difficult of access on account of the scarcity of water, evidence believed to be available had not yet been secured, and to supply this lack we attempted the trip. Dutton reported that all of the faults of this region were topographically recent, that wherever the faults were present cliffs of the upthrow side overlooked the lower 414 Report on fhe Geological Excursion downthrow side, and that the Sevier and Toroweap faults in this spe- cial district were separate and distinct. Professor Davis has recently advanced the theory that the faults are much more ancient, so ancient, in fact, that erosion has once obliterated the topographic effects of faulting by leveling off the country ; while recent erosion, removing the soft beds, has caused the reappearance of fault line cliffs wherever the old faulting brought hard and soft beds opposite each other, the cliffs thus facing toward the upthrow in some cases, toward the down- throw in others. Thus it was shown that the cliffs of today are often located on the side where the lowland was originally found, while the lowland of today has been worn out of the rocks which were faulted up, reversing the original topographic effects of faulting. Professor Davis further believed that the Sevier and Toroweap faults were continuous, being one and the same. A somewhat detailed study of the. region in question enables us to add a considerable amount of evidence which strongly corroborates the theory of a very great age for the faults, and which makes the theory of recent faulting wholly inadmissible. A traverse of some of the more inaccessible parts of the region, however, showed that the two faults were quite distinct, overlapping each other for many miles, but the Toroweap being from six to fifteen miles or more west of the southern extremity of the Sevier. The age of a part of the rock series of this region is in doubt because of the scarcity of fossil remains. We were fortunate in securing some fossils from the doubtful strata, which we hope will serve to establish their age more definitely. After returning from the Toroweap country we went westward to the Hurricane fault, and spent several days in camp on the bank of the Virgin River, waiting until one of the greatest floods in the river's history should subside sufficiently to enable us to ford. This enforced delay gave time for a careful study of the features of the fault scarp for several miles south of the river. This region has been described in some detail by Messrs. Huntington and Goldthwait in an admirable paper. They established the occurrence of two distinct periods of faulting along the great fracture with an intervening erosion period. A careful study of the relation of certain lava flows to the fault enabled us to discover a third period of movement or faulting quite as distinct as the two previously noted, with long time intervals separating it from those other periods. The relation of a number of successive lava flows and their effect on the former topography were worked out. Douglas Wilson Johnson 415 Northward from the Virgin our course lay along the foot of the western rim of the high plateaus on the eastern border of the Great Basin region. We traced the Hurricane fault for a hundred miles or more to the northward, studying the details of the faulting in many different localities. Recent faulting was discovered along the western side of Round Valley ; the stratigraphic series of that region was found to be quite unlike the representations on earlier maps, and the region was remapped as far as practicable. Some fossils were collected from the more recent members of the series. Collections of rhyolite, tra- chyte, and andesite from type localities were made for the purpose of supplementing the Institute study series. The character of the Tertiary beds in several regions was studied with regard to the question of their origin, and numerous observations of miscellaneous geological features were noted. As we neared the Salt Lake City region we had opportunity to observe the topographic features of the ancient shore lines of the former Lake Bonneville, type examples of dissected fault block moun- tains, and other features which have made this classic ground for all students of geology. The numerous photographs and sketches that were made of these typical features will add much to the effectiveness of the courses in topographic geology. In the villages and towns just south of Salt Lake City the outfit was disposed of and the party disbanded. Dr. Shimer went to the Yellowstone National Park for a short trip, Mr. Decker to the Bingham mining district, while I returned east by way of Butte, Montana. It will be seen that the results of the expedition include the col- lection of data bearing on a number of special problems of some scientific importance, as well as a variety of miscellaneous observations which should be permanently recorded. It is proposed to publish dis- ' cussions of the larger problems as separate reports during the coming year in different geological journals, and the miscellaneous observations, together with a brief abstract of the larger problems, as one report. Our party was in the field nearly four months, traveling over fifteen hundred miles by wagon and probably at least three hundred more on horseback. * O Vwwc.. ,y