RI0021D. Geology of Hood Spring Quadrangle, Brewster County, Texas, by R. W. Graves, Jr. 51 p., 4 figs., 1 map, 7 plates, 1954. RI0021D - Downloadable PDF.
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The Hood Spring quadrangle, in the central part of Brewster County, Texas, contains a segment of the southeast rim of the Marathon basin. It includes a part of the complexly folded and faulted Paleozoic rocks that occur in the center of the Marathon basin and also includes Cretaceous rocks exposed in the Maravillas scarp. This scarp has three stratigraphically separate cuestas that are formed by southeastward gently dipping beds. The southwestern corner of the quadrangle contains a faulted and folded segment of the Santiago Mountain range.
Rocks of Cambrian (Dagger Flat formation), Ordovician (Marathon, Alsate, Fort Peña, Woods Hollow, and Maravillas formations), Devonian (Caballos novaculite), and Pennsylvanian (Tesnus formation)ages occur in the area of Paleozoic outcrops. A conodont fauna from the upper part of the Caballos novaculite indicates a Middle to Upper Devonian age for those beds. Most of the Cretaceous rocks exposed in the quadrangle belong to the Comanche series (Glen Rose, Maxon, Walnut—ComanchePeak, Edwards, Kiamichi, Georgetown, Grayson, and Buda formations) and are similar to equivalent age strata in central Texas. Gulf series rocks (Boquillas and Terlingua formations) have a restricted occurrence in the southwestern corner of the quadrangle contains a faulted and folded segment of the Santiago Mountain range.
Tertiary intrusions include plugs, dikes, and sills of rhyolite, trachyte, and basalt which cut Cretaceous and Paleozoic rocks. These intrusives belong to the southern Trans-Pecos Texas suite of alkalic igneous rocks.
Keywords: Hood Spring Quadrangle, Brewster County, Texas, Marathon Basin, Maravillas scarp
Purpose and scope of the work
Climate and vegetation
Distribution of rocks
Dagger Flat sandstone
Fort Pena formation
Woods Hollow shale
Glen Rose formation
Walnut and Comanche Peak formations
Grayson (Del Rio) marl
Gravel mantle on pediments and rock floors
Rhyolites and trachytes
1. Index map showing Hood Spring quadrangle and adjacent quadrangles covered by published geologic reports
2. Cross section of Paleozoic rocks in the northwest corner of Hood Spring quadrangle in a ridge 1.5 miles east-northeast of Buttrill ranch
3. Sketch map and cross section of Caballos novaculite on north side of State highway No. 227, one-fourth mile southeast of Three-Mile Hill (Santiago Peak quadrangle), 17 miles south of Marathon, Texas
4. Representation of the fold and thrust fault which produced the ridge parallel to Maravillas Creek in the southwest part of Hood Spring quadrangle
I. Geologic map and structure sections of the Hood Spring quadrangle
II. Angular unconformity in Maravillas scarp
III. Caballos formation
IV. Cretaceous formations and Quaternary alluvium
V. Edwards limestone
VI. Igneous intrusives
VII. Geologic map and structure sections of the Maravillas Creek area
VIII. Geologic map and structure sections of the Tinaja Range area
Graves, R. W., 1954, Geology of Hood Spring Quadrangle, Brewster County, Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 21, 51 p. doi.org/10.23867/RI0021D.