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Solitario Uplift, Presidio-Brewster- Counties, Texas 1 BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA Vol. 32, pp. 417-428 December 1 , 1921 SOLITARIO UPLIFT, PRESIDIO-BREWSTER- COUNTIES, TEXAS 1 BY SIDNEY POWERS (Read before the Society December 29, 1920) CONTENTS P ag e Introduction........ 417 Summary............ 4 1 9 Regional geology 4 2 1 Detailed geology. 42 2 Stratigraphy. 42 2 Structure___ 4 2 5 Origin.................... 4 2 6 I ntroduction The Solitario is a circular dome 5 miles in inside and 7 miles in out­ side diameter, situated 60 miles south of Marfa, west Texas, in both Presidio and Brewster counties (figure 1). It is in the trans-Pecos sec­ tion, 9 miles in a straight line from the Rio Grande, on the western side of the “Big Bend” in the river and 25 miles east of Presidio. Occasional ranches are scattered through this barren mesquite desert, but few are near the highways. Military roads have been constructed from Marfa to Lajitas past the Solitario and to other outposts. There is a wagon road from the Lajitas road past McMahon’s ranch into the north end of the uplift. Although the Solitario is shown on the topographic sheet of the Ter- lingua quadrangle, United States Geological Survey (figure 1), and al­ though it has been visited by several geologists, including G. K. Gilbert, J. A. Udden, and R. T. Hill, nothing has ever been written about it.2 1 Manuscript received by the Secretary of the Society May 17, 1921. 2 It is shown on the “Geological map of a portion of west Texas,” by B. F. Hill and J. A. Udden, University of Texas Mineralogicai Survey, 1904 References to the Big Bend country are: J. A. Udden, A sketch of the geology of the Chisos country, Brewster (417) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/32/4/417/3414294/BUL32-0417.pdf by guest on 29 September 2021 418 SIDNEY POWERS— THE SOLITAltlO UPLIFT LEGEND E 3 S Igneous Rock H--- 1 Upper Cretaceous 1 I Lower Cretaceous Pennsylvanian pnvT] Devonian [?]. , iL-*----------1 (arrows show dips] Ordovician [?]. 1-SoIifario ---- Sections ito4 I- Marathon 7-Ouachita Mb 3- Shaft er 8-Muckle Mti.' K Silver Prospect 4 - Delaware Mb. 9-Wichita Mis. 5-Uano-Bumet 10-Amarillo Granite' Abandoned- 6-dend Arch11-Anton Chico Granite 12-Rid River Uplift '« 5 Miles 1-20 1_______ 2 3 ______ 4. ■*> Kilnmjytei-» Contour in terval lOO feet Datum is rnmxn sea level. F ig u r e 1 .— Geological Map of the Solitario Uplift, Presldio-Brewster Counties, Texas The accompanying outline map of Texas shows the relative position of the uplift to other areas of folding. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/32/4/417/3414294/BUL32-0417.pdf by guest on 29 September 2021 INTRODUCTION 419 The most remarkably symmetrical dome attracted the attention of the writer in 1919, in passing, and caused him to spend several days within it in 1920 in part in the company of Wallace E. Pratt, to whom he is indebted for many suggestions. Mr. W. S. Adkins and others of the Bureau of Economic Geology, Austin, Texas, have studied the area in detail, under the direction of Dr. TJdden, and the present brief descrip­ tion is preliminary to their report. * Summary Geologically, the Solitario consists of an unroofed, steep-sided, flat- topped dome formed of Lower Cretaceous limestones, within which there is an eccentric dome of steeply tilted Ordovician cherts, limestones, and shales, Devonian (?) novaculite, Pennsylvanian shales and sandstones, and Permian limestones. A portion of the Cretaceous cover is preserved in the center of the dome on a high ridge which runs from east to west. South of this ridge the Pennsylvanian shales and sandstones on the south side of the Ordovician dome are cut and in part covered or replaced by volcanic breccias and intrusives (figure 2). Volcanic activity is every­ where visible in dikes, sills, and laccoliths, the most extensive sill being within 20 to 100 feet of the base of the Cretaceous and extending around a great part of the periphery of the dome, as well as through the inlier in the center. Solitario Peak is an igneous mass, probably a volcanic plug, and an unnamed hill on the north is a laccolith, but no attempt is made to map or describe the other igneous masses. The Solitario and the Marathon uplift, 60 miles northeast, are part of an area mountain-built in Permian time and later buried. The broad and gentle uplift of the latter after Cretaceous deposition is believed to have resulted from compression at right angles to the direction of the earlier forces. The very abrupt and symmetrical doming of the Solitario may be accounted for in the same manner or possibly by a laccolithic intrusion in basal Paleozoic strata. The Cretaceous cover of the Solitario County, Texas, University of Texas, Bulletin 93, 1907 ; J. A. Udden, Notes on the geology of the Glass M ountains; and C. L. Baker and W. F. Bowman, Geologic exploration of the southeastern Front Range of trans-Pecos, Texas,.University of Texas, Bulletin 1753, 1917; J. A. Udden, C. L. Baker, and E. Böse, Review of the geology of Texas, University of Texas, Bulletin 44, 1916 ; R. A. Liddle, The Marathon fold and its influence on petro­ leum accumulation, University of Texas, Bulletin 1847, 1918 ; B. F. Hill, The Terlingua quicksilver deposits, Brewster CGunty, University of Texas, Bulletin 15, 1902 ; T. W. Vaughan, Reconnaissance in the Rio Grande coal fields of Texas, U. S. Geological Survey, Bulletin 164, 1900; -T. A. Udden, The anticlinal theory as applied to some quicksilver deposits (Terlingua District, Brewster County), University of Texas, Bulletin 1822, 1918. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/32/4/417/3414294/BUL32-0417.pdf by guest on 29 September 2021 on 29 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/32/4/417/3414294/BUL32-0417.pdf 420 420 SIDNEY SIDNEY THE POWERS---------------------------------------------------------------------------------------------------------------------------------------------------------- SOLITARIO UPLIFT X'Xn WNE0U5 POCK ] LOWER CPETACEOUS | . ; . ;.} DEVONIAN (?) NOVACULLTE UPPER CRETACEOUS \ PENN-LIMESTONE & SHALE [ : r r ^ ORDOVIOAN C?J LIMESTONE & SHALE F ig u r e 2.—Cross-sections of the Solitario Uplift GEOLOGY OF THE REGION 421 has been fractured by faults and by volcanic intrusions and extrusions and largely eroded. R e g i o n a l G e o l o g y The Big Bend country and the area to the northward comprise the volcanic plateau of western Texas. A vast region is covered by lava flows and ash beds or by bolson deposits which conceal the bedrock. Cretaceous rocks are exposed at the edges of, and occasionally within, the volcanic area. That volcanic activity began during the Upper Cretaceous and con­ tinued into the Tertiary is shown by plant remains.3 The lavas are ande- sitic and rhyolitic in character and they are described by Dr. Whitman Cross in an unpublished manuscript of the United States Geological Sur­ vey by Mr. E. T. H ill on the Big Bend country. Both flows and ash beds can be traced for many miles in mesas, and the good exposures invite careful mapping and study. Structure of the Big Bend region must be considered for the Paleozoic and Cretaceous terranes separately. The younger, as shown to the writer by Mr. H ill and later observed in the field, forms a high plateau 100 miles in width, broken on either side by fault blocks tilted toward the plateau.4 The faults on the east are in the Boquillas (Carmen) Moun­ tains; those on the west are in the Sierra Vieja Mountains. Many other faults with profound escarpments, like those south of Lajitas and Ter- lingua, add complexity to the structure. In spite of these fractures, the Rio Grande has maintained its course developed during the igneous activity, and the only sedimentary records of the canyon-cutting stage, as interpreted by the writer, are part of the very thick bolson deposits between Presidio and El Paso. In Mexico, the Burro Mountains south­ east of the Big Bend represent block-faulted Cretaceous mountains cut by intrusions. Paleozoic rocks outcrop at only four localities in the Big Bend region— Marathon, the Solitario, Shafter, and west of the Chinati Mountains, in Pinto Canyon * (undescribed). The nearest Paleozoic areas are the Guadalupe and Delaware Mountains to the north (figure 1) and the Llano-Burnet (Central Mineral) region to the east. The former is 3 E. W. Berry : An Eocene flora from trans-Pecos, Texas. U. S. Geol. Survey, Profes­ sional Paper 125A, 1919. 4 C. L. Baker described this plateau as a block relatively less elevated than any other part of the trans-Pecos (Review of the Geology of Texas, University of Texas, Bulletin 44, 1916, p. 15). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/32/4/417/3414294/BUL32-0417.pdf by guest on 29 September 2021 422 SIDNEY POWERS----THE SOLITARIO UPLIFT clearly a part of the Cordilleran region. The latter is a block-faulted uplift comparable to a horst, which shows very gentle folding. It forms the southern end of the Bend arch. The Paleozoic rocks in the Solitario and Marathon areas show the same northeast-southwest strike, but the continuation of this line of folding has not been traced beneath the younger sediments. On the north side of the Marathon area the Glass Mountains, composed of a great thickness of Permian limestones, mark, locally, the southern limit of a series of Permian sediments unconform- able with the earlier Permian, which extend into New Mexico with abrupt lithologic change.
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