The recent visits of a number of the members of the Academy to the Tulerosa district and contiguous plains in New Mexico makes it seem worthwhile to call attention to some of the major geologic structures of the region

Keyes, Charles R.

English

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 12 Annual Issue Article 28 1904 Geological Structure of the Jornada del Muerto and Adjoining Bolson Plains Charles R. Keyes Copyright ©1904 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Keyes, Charles R. (1904) "Geological Structure of the Jornada del Muerto and Adjoining Bolson Plains," Proceedings of the Iowa Academy of Science, 12(1), 167-169. Available at: https://scholarworks.uni.edu/pias/vol12/iss1/28 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. IOWA ACADEMY OF SCIENCES. 167 The Sierra Oscura-San Andreas range presents some features which are quite different from those already men-tioned, which may be partly due to faulting at the time the blocks were tilted. The two parts of the range overlap somewhat, and dip in opposite directions. The major fault plane along which the block was upraised lies on dif-ferent sides of the two parts of the range. Between the two parts is a flat plain, several miles wide, which, how-ever, is considerably elevated above the plains on either side of the great ridge. The mountains are capped by Carboniferous limestones; so also is the small plain between. The section appears to be as follows (figure 7): FIG. 7. Fault Block between the Sierra Oscura and San Andreas Range Displacement 2, 600 feet. GEOLOGICAL STRUCTURE OF THE JORNADA DEL MUERTO AND ADJOINING BOLSON PLAIN~. BY CHARLES R. KEYES. The recent visits of a number of the members of the Academy to the Tulerosa district and contiguous plains in New Mexico makes it seem worth while to call attention to some of the major geologic structures of the region. The section represented below is in an east and west direction through the station of Engle on the Atchison, Topeka & Sante Fe railroad, reaching beyond Alama.gordo on the El Paso & Northeastern railroad. 1Keyes: Geological Structure of the Jornada del Muerto and Adjoining BolsPublished by UNI ScholarWorks, 1904168 IOWA ACADEMY OF SCIENCES. The section shows for the J ornada plain a simple synclinal structure, with profound faults on the opposite side of the marginal mountain ranges in either direction. On the Rio Grande side of the Caballos range repeated faulting is indicated-the river occupying the minor fault-blocks next the great fault-block of the main mountain ridge. ' . . Rio .' / · · ~J"orn..J.odd Muerto 1 Tul&oos~ LJ. i.:.. CZLL \ z FIG. 8. Geological Structure of Jornada and Tularosa De1erts. ' ' The highest part of the Caballos exhibits very clearly the evidences of a profound thrust-plane the geological age of which greatly antedates the period of normal block faulting which givee the present characteristic aspects to the region. The Carboniferous limestones for a distance of three-fourths of the distance to the summit of the range stand nearly vertically. Erosion has bevelled the stratification planes at angles of about 35 degrees-the slope of the eastern side of the range. This imparts to all except the upper part of the mountain faca a remarkably contorted appearance, with horizontal beds of the same com-position capping the summit. The effect is almost inex-plicable until the position of the thrust-fa.ult is recognized. Immediately east of the western rim of the bolson and between the Sierras de los Caballos and Fra Cristobal are a number of small lava cones 300 to 400 feet high, each of which send out a basalti.c fl.ow for several miles in all directions from its center. These basalt flows appear to cover some of the earlier mesa gravels. They are quite recent-probably early Pleistocene in age. The gentle syncline of the J ornada is perhaps its most characteristic structural feature. It is to be noted, however, that this region is not a simple trough but a syncline which has experienced repeated, or rather continued, upturning 2Proceedings of the Iowa Academy of Science, Vol. 12 [1904], No. 1, Art. 28https://scholarworks.uni.edu/pias/vol12/iss1/28IOWA ACADEMY OF SCIENCES. 169 of ~ts margins while the process of general base leveling was gomg on. In the San Andreas range there is found a simple mono-clinal block. The profound faulting is on the eastern flank of the range. From the foot extends another broad bolson plain extending to the foot of the lofty Sierra Blanca. The faults represented indicate displacements of 3,000 to 5,000 feet. NORTHWARD EXTENSION OF THE LAKE VALLEY LIMESTONE. BY CHARLES R. KEYES. As a terranal name Lake Valley is applied to a remarka-ble blue limestone occurring at the famous silver mining camp of the same title, situated in Sierra county, New Mexico. The formation is noteworthy for the reason that it carries the typical Lower Burlington fauna of Iowa. On this account it is of special interest to Iowa geologists. The first recognition of the Lower Burlington fauna, a thousand miles away from the original locality, is due to Mr. Fra.nk Springer, a former Iowan, and the leading authority on American crinoids.* · At Lake Valley the limestone bearing thatname is, as at Burlington, crinoidal in character. Mr. Springer, in the article cited, furnished a considerable list of crinoids as well as of other fossils, all of which are the most charac-teristic forms of the Lower Burlington limestone of south-eastern Iowa. Since the appearance of the paper men-tioned, twenty years ago, no further reference has ever been made to the Burlington fauna in southwestern United States. *Am, Jour. Sci, (3), Vol. XXVII, pp. 97·103, 1884. 3Keyes: Geological Structure of the Jornada del Muerto and Adjoining BolsPublished by UNI ScholarWorks, 1904

Geological Structure of the Jornada del Muerto and Adjoining Bolson Plains

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Geological Structure of the Jornada del Muerto and Adjoining Bolson Plains

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