Geologic Quadrangle Maps

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    Geologic map of the Austin west quadrangle, Travis County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1970) Rodda, Peter U.
    The rocks exposed in the Austin West quadrangle are Cretaceous marine limestones and clays and Quaternary alluvial deposits. The Cretaceous rocks dip gently eastward and are broken by one large (Mount Bonnell) fault and numerous small, northeast-trending faults comprising the Balcones fault zone. Most faults are downthrown to the east; total displacement across the fault zone is about 1,000 feet. M.ost of the quadrangle is west of the fault zone in the highly dissected hill country; the rocks consist mostly of interbedded hard and soft limestone, dolomite, and marl (Glen Rose, Walnut, and Edwards Formations). In the Balcones fault zone limestone units (Edwards, Georgetown, and Buda Formations) and clay units (Del Rio Clay and Eagle Ford Formation) are complexly faulted and moderately to strongly dissected. In the southeast corner of the quadrangle limestone (Austin Group) and clay (Eagle Ford Formation) crop out at the west margin of the blackland prairie. The Colorado River flows across the area from northwest to southeast, and six terrace deposits (Sand Beach, Riverview, First Street, Sixth Street, Capitol, and Asylum) consisting mostly of sand and gravel parallel the river and occupy successively higher topographic positions; the deposits are more extensixe east of the Mount Bonnell fad. Other alluvial deposits are developed along tributary streams. The limestone units generally are stable and resistant, are difficult to excavate, have mostly moderate to high permeability, and pose few engineering problems; they are sources of crushed stone and other building materials; one unit (Edwards Formation) is an important aquifer. The clay units are weak, unstable, impermeable, and corrosive and generally require special engineering designs. Alluvial deposits are easily excavated, have moderate to low stability and strength, have high permeability, and may need special designs for large structilres; the deposits are important aquifers and sources of sand and gravel.
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    Geologic map of the North Grape Creek quadrangle, Blanco and Gillespie Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1952) Barnes, Virgil E. (Virgil Everett), 1903-1998
    North Grape Creek quadrangle is south of the Llano region and is mostly in the broad Pedernales River basin. A few outliers of the Edwards Plateau are present in the western part of the quadrangle. The geology of the North Grape Creek quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Fredericksburg quadrangle. Elevations ranging between 1,294 and 1,775 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, it is estimated that the relief within the quadrangle is about 640 feet, ranging between about 1,200 and 1,840 feet in elevation. The quadrangle is entirely within the Pedernales River drainage basin and is mostly drained by North Grape Creek and its tributaries, some of which are White Oak Creek, Basin Spring Hollow, Dry Hollow, and Smith Spring Branch. The southern part of the quadrangle is drained by Pedernales River and its branches, some of which are Iron Rock Creek and Rocky Creek. North Grape Creek quadrangle is high on the southeastern side of the Llano uplift, and rocks from pre-Cambrian to Ordovician in age outcrop in about three-quarters of the quadrangle. Faults related to the Ouachita orogeny trend mostly northeast-southwest; some trend east-west. The Cretaceous rocks are essentially horizontal, dipping eastward perhaps about 10 feet per mile. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region cannot be given in the space available. References cited below deal with some of the problems. This publication on the North Grape Creek quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to this index map to locate other quadrangles mentioned in the present text.
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    Geologic map of Black Gap area, Brewster County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1966) St. John, Bill, 1932-
    The wedge-shaped Black Gap area in southern Brewsier County, Texas, occupies approximately 4,50 square miles east of the Big Bend National Park. The southwestern boundary of the map area is the castcrn boundary of the Park; the southeastern boundary is the Rio Grande; the north boundary is drawn at lat. 29' 45' N. The area lies in the Trans-Pecos proxince and throughout this arid to semiarid region the climate, flora, and fauna are similar. The Black Gap region can be divided into four physiographic areas: (1) the topographically high and imposing Sierra del Carmen to the southwest, which is an area of stepped plateaus separated by steep, northwest-trending scarps; (2) the Cupola iWountain highland in the northeast corner of the map area; (3) a topographically low area extending from the Rio Grande northwest through the middle of the Black Gap area and characterized by low, steep-sided hills capped with basalt; and (4,) the gravel-covered lowland to the northwest which is an area of low, rounded hills.
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    Geologic map of the Stonewall quadrangle, Gillespie and Kendall Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1966) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Stonewall quadrangle includes part of the southern margin of the Llano region and part of the eastern margin of the Edwards Plateau where most of the plateau suriace has been destroyed by erosion. An east-northeastward-trending lobe of the Edwards Plateau crosses the quadrangle near its southeastern corner. The area to the north is in the broad gently rolling Pedernales River basin, and that to the southeast is in a more rugged marginal part of the Blanco River drainage area. The geology of the Stonewall quadrangle is shown on a U.S. Geological Survey 7.5-minute topographic quadrangle map (contour interval 20 feet, scale 1:24,000) which covers the same area as the Stonewall quadrangle planimetric map, scale 1:31,680 (Barnes, 1952i). The relief in the quadrangle is about 600 feet; elevations range from about 1,395 feet where Pedernales River leaves the quadrangle to about 1,995 feet at the highest point on the Edwards Plateau. The quadrangle is mostly drained by Pedernales River and its tributaries- Blumenthal, Cave, Roundhead, Threemile, and South Grape Creeks, Beckman, Gellerman, Salt, and Arnelger Branches, and other unnamed drainages. In the southeasternmost part the drainage is southward to Blanco River. Stonewall quadrangle is high on the southern side of the Llano uplift. Cambrian and Ordovician rocks occur in patchy outcrops in the vicinity of Pedernales River and northward. Cretaceous rocks and some Quaternary surficial deposits occupy the remainder. The one fault within the quadrangle is related to the subsurface Ouachita structural belt (Flawn et al., 1961, pp. 65-81) and trends northeast-southwest. The Paleozoic rocks mostly dip gently southward to southwestward at angles up to about 8 degrees, and the relatively flat-lying Cretaceous rocks dip eastward about 10 feet per mile. This publication on the Stonewall quadrangle is the fourth of a series of Central Texas geologic quadrangle maps which are being compiled as topographic bases become available. An index map for geologic maps already published on planimetric and topographic bases and others planned for publication on the new topographic bases is shown with the geologic map. During the period 1939- 1947, the writer, assisted by Louis Dixon, mapped geologically and made a gravity survey of the Stonewall quadrangle.
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    Geologic map of Eagle Mountains and vicinity, Hudspeth County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1963) Underwood, James R.
    Eagle Mountains and vicinity include three physiographically distinct but stratigraphically and structurally related sub-units: a central, topographically high mesa, Eagle Mountains; a much lower northwestward extension, Devil Ridge; and a south-southeastward extension, Indio Mountains. These highlands, trending generally northwest to north-northwest, are surrounded by "bolsons" or inter- montane basins partly filled with alluvium. This area is an extension into southeastern Hudspeth County of the eastern part of a long, narrow, mountainous, structural belt that begins some 150 miles southeast near Ojinaga, Chihuahua, Mexico. The summit of Eagle Peak, 17 miles south- west of Van Horn, Culberson County, and 24 miles southeast of Sierra Blanca, Hudspeth County, is 7,496 feet above sea level, the highest point in Hudspeth County. The lowest point in the map area, the southeastern corner along the Rio Grande, is 3,150 feet above sea level; the maximum difference in elevation is about 4,350 feet. In the highlands, well-exposed rocks ranging in age from Precambrian to Re- cent include about 5,000 feet of meta- morphosed Precambrian sedimentary rocks, at least 1,000 feet of Permian lime- stone, and about 7,000 feet of marine Cretaceous strata, much of which is cov- ered by an early Tertiary volcanic rock sequence of flow breccia and fine-grained flow and pyroclastic rocks. Small intrusive bodies, mainly sills and dikes, crop out throughout the area; the highest part of the Eagles is a small, roughly semi- circular stock. The range is flanked by well-defined alluvial fans and terraces. The stratigraphy of the Cretaceous rocks was controlled by a fluctuating shoreline during the general advance of the Cretaceous sea north and east from the Chihuahua trough onto the Diablo Platform and the continental margin; structurally, the spatial relationships of the Cretaceous rocks were controlled by their location (1) on the southwest flank of the Van Horn uplift, (2) near the northwest end of the Laramide Chihuahua tectonic belt, and (3) near the eastern margin of the Basin-and-Range province.
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    Geologic map of the Hye quadrangle, Blanco, Gillespie, and Kendall Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1965) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Hye quadrangle includes part of the southeastern Llano region and part of the eastern margin of the Edwards Plateau where most of the Plateau surface has been destroyed by erosion. In the southern part of the quadrangle a narrow lobe of the Edwards Plateau trends east-northeastward from near the southwest quadrangle corner. The area to the north is in the broad gently rolling Pedernales River basin, and that to the south is in a fairly rugged marginal part of the Blanco River drainage area. The geology of the Hye quadrangle is shown on a U. S. Geological Survey 7%-minute topographic quadrangle map and, following the Johnson City quadrangle (Barnes, 1963), is the second geologic map in the Llano region to appear on a modern 1:24,000 scale, 20-foot contour interval base. The relief in the quadrangle is about 591 feet; elevations range from about 1,362 feet where Pedernales River leaves the quadrangle to 1,953 feet near the southwest corner of the quadrangle. About 80 percent of the Hye quadrangle is drained by Pedernales River, mostly through two main tributaries, Williamson and Rocky Creeks, both of which have three forks-East, Middle, and West-and numerous named and unnamcd tributaries. The remaining 20 percent of the quadrangle drains to Blanco River by way of Klepac Creek, Stiner Creek, Murry Branch, Roman Branch, and various unnamed branches. During the time the geology of this area was being mapped, Klepac Creek was known as North Big Creek and Stiner Creek as West Big Creek. Hye quadrangle is high on the southeastern side of the Llano uplift. Cambrian and Ordovician rocks are represented by about 1 square mile of outcrop. Cretaceous rocks and small Quaternary surficial deposits occupy the remainder. The Cambrian and Ordovician rocks exposed in the northeastern part of the quadrangle dip southeastward at angles up to about 5O, and the relatively flat-lying Cretaceous rocks dip eastward about 10 feet per mile. Discussion of stratigraphic, structural, economic, and geophysical problems are in cited references. This publication on the Hye quadrangle is one of a series of central Texas geologic quadrangle maps which will be compiled as topographic bases become available. An index map for geologic maps already published on planimetric bases and others planned for ~ublication on the new topographic bases is shown with the geologic map. During the period 1939 to 1942, the writer, assisted by Louis Dixon, mapped geologically the western one-third of the Hye quadrangle in Gillespie and Kendall counties. Mapping of the remainder of the quadrangle area, in Blanco County, was done intermittently with assistance from L. E. Warren (1942-194,G) and A. R. Palmer (1947- 1948). A gravity survey of the quadrangle was completed during 1946-1948 with the aid of Louis Dixon and A. R. Palmer.
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    Geologic map of eastern half of Kent quadrangle, Culberson, Reeves and Jeff Davis Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1962) Brand, John Paul
    Study of Permian, Cretaceous, and Cenozoic rocks in the 30 Kent quadrangle is important to an understanding of the geology of Trans-Pecos Texas. Most of the Cretaceous rock units of central Texas lose their lithostratigraphic identity when traced into west Texas. The Kent quadrangle, astride the Diablo Platform, is one of the critical areas of intervening stratigraphy between central Texas to the east and the geosyncline in Mexico to the west and southwest. Permian units have been studied extensively in areas of outcrop in west Texas and stratigraphic relationships of the Permian beds are fairly well known. Likewise, subsurface Paleozoic units within the Delaware basin are well known. To the southwest, beyond the margin of the Diablo Platform, surface and subsurface Permian rocks are in completely known. It is hoped that a study of the younger rocks in the latter area might reveal characteristics which will possibly reflect late Paleozoic tectonic elements. The accompanying map, covering the area bounded by 10400 and 10415 west and 3100 and 3130 north, is the first of a series of areal geologic maps of the region. Ad- joining areas are currently under investigation by several workers. The Kent region is arid; numerous intermittent streams, the largest of which are Cottonwood Draw, China Draw, Salt Draw, San Martine Draw, and Hurd Draw, drain the area. Cottonwood Draw (King, 1949) rises west of the Kent quadrangle and flows eastward across the Gypsum Plain (Richardson, 1904, p. 22); its course lies mostly outside the map area. Salt Draw and China Draw also rise in a gypsum terrain and trend castwardly through the central part of the quadrangle. Hurd Draw and San Martine Draw rise in the Davis Mountains. Cottonwood Draw discharges into the Toyah basin but does not reach the Pecos River. The others ultimately discharge into Toyah Lake southeast of Pecos, about 45 miles northeast of Kent, and the overflow from the lake enters the Pecos River. Thus the Toyah basin is a semi-bolson (Tolman, 1909, p. 141). Most of the annual rainfall of 13 inches occurs as thunder showers during the summer months; immediately following heavy rains, stream channels flood to truncated collapsed units. Probably the age of the major collapse is pre-Gatuna; perhaps the dissolving of the gypsum began late in the Tertiary Period after the regional uplift that accompanied the block faulting farther west. The profusion of faults of low displacement in the vicinity of Davis Mountain Station can probably be attributed to solution of the Castile Gypsum. Undoubtedly, many similar faults are concealed beneath the alluvium in the flat in the central portion of the area.
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    Geologic map of Van Horn Mountains, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1959) Twiss, Page C., 1929-
    About 10 miles south of Van Horn, Texas, the Van Horn Mountains rise abruptly above an intermontane plain and extend southward to the Sierra Vieja. The area lies primarily in the southwestern part of Culberson County but extends into Hudspeth and Jeff Davis counties. The mountains owe their present topographic form to late Tertiary block-faulting. Structurally, they are a northward-trending horst which is flanked on the east and west by intermontane basins. The basin east of the mountains is herein named "lobo bolson": although structurally separate, it is topographically a southern extension of Salt Basin. An outcrop (30 46.5 N., 105 55.5' W.) of Tertiary volcanic rock separates two structural basins west of the mountains: the southern basin is herein named "Green River bolson." Topographically, the northern part of the northern basin is a southeastern extension of Eagle Flat. In addition to the major, generally north-south high-angle normal faults that define the horst, many normal faults of lesser magnitude cut the highland mass of the Van Horns; they are either nearly parallel to or at large angles to the strike of the horst. In the southern part of the area are three thrust faults of Laramide age. Older Comanchean strata on the west are thrust over younger Cretaceous strata on the east. These faults occurred before the outflow of lava in the Davis Mountains. The northern segment of the mountains, where Precambrian metasedimentary rocks are exposed, is within the southern boundary of the Van Horn uplift. Rocks of Permian, Cretaceous, and Tertiary age dip generally to the south at about 4 degrees. The area lies along the junction of the Chihuahua tectonic belt on the west and Diablo Platform on the east. The Tertiary volcanic rocks are part of the Davis Mountains lava field, which is the greatest exposure of volcanic rock in Texas. Stream flow of the region is intermittent. Salt Basin, collecting water from Eagle Flat and from the northern and eastern parts of the Van Horn Mountains, is a prominent basin of interior drainage. Water flows northward from Lobo Flat to Salt Basin through Wildhorse Draw. After cloudbursts, water from Eagle Flat flows through the gap between the north end of the Van Horns and the south end of the Carrizo Mountains and joins Wildhorse Draw. Green River, which empties into the Rio Grande, receives water from the western part of the area. Hence, the eastern intermontane basins are being filled with sediment, while outcrops of the Green River bolson are being eroded and the sediment transported to the Gulf of Mexico. In Lobo Flat as much as 1,200 feet of alluvium covers the bedrock, and at the head of Green River, the alluvium is at least 1,100 feet thick. Previous workers have contributed much to the knowledge of the area. Baker (1927) included the Van Horn Mountains in his regional study of Trans-Pecos Texas. Flawn (in King and Flawn, 1953) mapped the Precambrian rocks exposed in the Carrizo Mountains and in the northwestern and northeastern sectors of the Van Horns; summaries of his petrographic descriptions are included in this report. The southern third of the area was mapped by The University of Texas graduate students C. G. Havard, R. I. Ellsworth, E. R. Kennedy, and R. N. Throop in 1948 and P. Braithwaite and D. R. Frantzen in 1957. This study is part of a Bureau of Economic Geology project of geologic mapping in Trans-Pecos Texas. The writer gratefully acknowledges the valuable suggestions of Professor R. K. DeFord and Dr. John T. Lonsdale on stratigraphic and petrographic problems, respectively. Dr. K. P. Young identified the Cretaceous fossils. John W. Trammell ably assisted in the field in 1957, and Charles E. Clark in 1956. This report is part of a doctoral dissertation prepared under the supervision of Professor DeFord. Although the base of this unit is covered, the writer believes that it overlies the Hueco limestone; the dip of these beds is similar to that of the Hueco beds to the north. This unit is about 60 feet thick. Limestone member (Pv!)The basal member of the Victorio Peak grades upward into a medium- to thick-bedded, unfossiliferous, dolomitic limestone. On fresh surfaces, the color grades upward from brownish-black to medium gray; it weathers to pale orange. Bedding is well developed; the beds are from 6 to 15 inches thick. Differential weathering produces a horizontal fluting parallel to bedding. The rock is finely crystalline and composed of clear crystalline calcite patches scattered throughout a finely crystalline dolomite matrix. About 180 feet were measured in the Van Horn Mountains; no upper contact was observed. This unit is similar to the limestone member (Pv1) of the Victorio Peak formation that crops out in the Wylie Mountains (Hay-Roe, 1957). The age is probably Leonard.
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    Geologic map of the Fall Prong Quadrangle, Kimble, Gillespie and Mason Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1956) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Fall Prong quadrangle is in the marginal portion of the Edwards Plateau near the southeastern corner of the Llano region. Almost three-quarters of the quadrangle is within the Edwards Plateau, and the rest consists of valleys of the Llano basin cutting back into the plateau. The geology of the Fall Prong quadrangle is shown on a planimetric map; the only topographic map available is the reconnaissance 30-minute Kerrville quadrangle. Elevations ranging between 1,723 and 2,245 feet were determined during traversing for control, but the lowest elevation was not reached. However, it is estimated that the relief within the quadrangle is about 545 feet, ranging between about 1,700 and 2,245 feet. The quadrangle is entirely within the Llano River drainage basin. Most of it drains into the James River via Little Devils River, with important branches being Fall Prong and White Oak Creek. Salt Branch in the northwestern corner flows directly to James River. A small area in the southeastern part of the quadrangle drains into Threadgill Creek and reaches the Llano River via Beaver Creek. The Fall Prong quadrangle is well up on the southwestern side of the Llano uplift and is covered by Cretaceous rocks which crop out over the entire quadrangle except in the northwestern part where Cambrian and Ordovician rocks appear. One fault formed during the Ouachita orogeny (Barnes, 1948) is exposed. The Cretaceous rocks are essentially horizontal and may dip as much as 6 feet per mile southeastward in most of the quadrangle. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region are in references cited below. This publication on the Fall Prong quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to the index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Dry Branch Quadrangle, Kerr and Gillespie Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1954) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Dry Branch quadrangle is in the Edwards Plateau province southwest of the Llano region. It is near the margin of the plateau, and Johnson Creek and some of its tributaries, such as Dry Branch, Falls Branch, Fessington Branch, and Welch Branch, have cut into the plateau in the southern part of the quadrangle. The geology of the Dry Branch quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Kerrville quadrangle. Elevations ranging between 1,819 and 2,254 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, it is estimated that the relief within the quadrangle is about 460 feet, ranging between about 1,800 and 2,260 feet. The quadrangle is mostly within the Guadalupe River drainage basin and is drained by Johnson Creek and its tributaries, such as Fall Branch, Dry Branch, Fessington Branch, Welch Branch, Smith Branch, Rough Hollow, and Bad Man Draw. Klein Branch and Scott Branch, tributaries of the Pedernales River, drain the northeastern portion of the quadrangle. Dry Branch quadrangle is on the southwestern side of the Llano uplift, and Cretaceous rocks crop out in all of the quadrangle. The depth to faulted and gently dipping Paleozoic rocks is probably only a few hundred feet beneath the more deeply incised streams. Essentially horizontal Cretaceous rocks form the outcrops in the quadrangle. Broad discussions of the stratigraphic, structural, economic, and geophysical problems of the region are given in references cited below. This publication on the Dry Branch quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to the index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Harper Quadrangle, Gillespie County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1954) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Harper quadrangle is in the Edwards Plateau province south of the Llano region. The plateau surface within the quadrangle is dissected by the Pedernales River and its tributaries in the southern part, and by Threadgill and Edwards Creeks in the northern part. The geology of the Harper quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Kerrville quadrangle. Elevations ranging between 1,891 and 2,226 feet were determined during traversing for control, but only the highest point was reached. The lowest point is somewhere in the southeastern part of the quadrangle and is estimated to be at an elevation of about 1,800 feet, giving about 425 feet of relief for the quadrangle. About two-thirds of the quadrangle is directly drained by Pedernales River and its branches. The northern third of the quadrangle is in the Llano River drainage basin and is drained by Edwards Creek, Maverick Spring Branch, and the headwaters of Threadgill Creek, which reach Llano River by way of Threadgill Creek and Beaver Creek. The Harper quadrangle is on the south side of the Llano uplift, and Cretaceous rocks crop out in all of the quadrangle. Rocks of Cambrian and Ordovician age are not far beneath the more deeply incised streams. The Cretaceous rocks are essentially horizontal and may dip 2 or 3 feet per mile to the northwest. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region are given in references cited below. This publication on the Harper quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to the index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Wendel Quadrangle, Kimble, Kerr, and Gillespie Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1954) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Wendel quadrangle is entirely within the Edwards Plateau province and is situated southwest of the Llano region. The geology of the Wendel quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Kerrville quadrangle. Elevations ranging between 2,041 and 2,284 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, it is estimated that the relief within the quadrangle is about 270 feet, ranging between 2,020 and 2,290 feet. The quadrangle has diverse drainage patterns. About half the drainage flows westward and northward to Little Devils River, ultimately reaching the Llano River by way of James River. White Oak Creek, Fall Prong, and Burr Oak Draw are the chief tributaries of Little Devils River. The headwaters of the Pedernales River occupy about one-third of the quadrangle, centered in the southeastern part. A small area in the northwest corner drains into Threadgill Creek and then into Beaver Creek and Llano River. A small area in the southwestern part of the quadrangle is in the Guadalupe River drainage basin, reaching the river by way of Rough Hollow and Johnson Creek. The Wendel quadrangle is on the southwestern side of the Llano uplift, and Cretaceous rocks crop out throughout the quadrangle. Rocks of Ordovician and Carboniferous age are probably less than a thousand feet below the surface. The Cretaceous rocks are essentially horizontal. References cited below deal more broadly with some of the stratigraphic, structural, economic, and geophysical problems of the region. This publication on the Wendel quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to the index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Cain City Quadrangle, Gillespie and Kendall Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1952) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Cain City quadrangle is south of the Llano region and is in the marginal portion of the Edwards Plateau where much of the plateau surface has been destroyed by erosion. Northeastward-trending lobes and outliers of the Edwards Plateau are present in the southern part. The rest of the quadrangle is in the gently undulating broad Pedernales River basin. The geology of the Cain City quadrangle is shown on a planimetric map since the only topographic map available is the reconnaissance 30-minute Fredericksburg quadrangle. Elevations ranging between 1,512 and 1,932 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, from the traverse it is estimated that the relief within the quadrangle is about 500 feet, ranging between about 1,500 and 2,000 feet in elevation. The quadrangle is entirely within the Pedernales River drainage basin and is mostly drained by South Grape Creek, Meusebach Creek, and numerous short branches of Pedernales River. Barons Creek and Palo Alto Creek empty into Pedernales River within the quadrangle. The Cain City quadrangle is on the southern side of the Llano uplift, and rocks of Ordovician age outcrop as inliers surrounded by Cretaceous rocks. The faulting accompanying the Ouachita orogeny (Barnes, 1948) is not exposed but southeastward dips up to 8 are present in the Paleozoic rocks. The Cretaceous rocks are essentially horizontal, dipping mostly southward about 8 feet per mile. A gentle nose with a southeastward trend is present, and one of the few faults in Cretaceous rocks noted in the vicinity of the Llano uplift is in the southern part of the quadrangle. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region cannot be given in the space available. References cited below deal with some of these problems. This publication on the Cain City quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to this index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Stonewall Quadrangle, Gillespie and Kendall Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1952) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Stonewall quadrangle is south of the Llano region and is in the marginal portion of the Edwards Plateau where much of the plateau surface has been destroyed by erosion. Along the southern edge, lobes of the Edwards Plateau are present, which coalesce southward to form a continuous narrow east-west plateau belt part of which is just south of the Stonewall quadrangle. Most of the quadrangle is within the gently undulating, broad Pedernales River basin. The geology of the Stonewall quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Fredericksburg quadrangle. Elevations ranging between 1,423 and 1,969 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, it is estimated that the relief within the quadrangle is about 600 feet, ranging between about 1,400 and 2,000 feet in elevation. The quadrangle is largely within the Pedernales River drainage basin and is mostly drained by Three Mile Creek, South Grape Creek, and its tributary Dry Creek. Cave Creek enters the Pedernales River within the quadrangle, and other important branches drain a considerable area in the vicinity of the river. A small area in the southeastern corner of the quadrangle is drained by branches of the Blanco River. The Stonewall quadrangle is high on the southern side of the Llano uplift, and rocks of Cambrian and Ordovician age outcrop in the northern part as inliers surrounded by Cretaceous rocks. Faulting related to the Ouachita orogeny (Barnes, 1948) is present. The Cretaceous rocks are essentially horizontal, dipping eastward about 10 feet per mile. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region cannot be given in the space available. References cited below deal with some of these problems. This publication on the Stonewall quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to this index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Squaw Creek Quadrangle, Gillespie and Mason Counties, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1952) Barnes, Virgil E. (Virgil Everett), 1903-1998
    The Squaw Creek quadrangle is partly within the Llano region and partly within the Edwards Plateau province. The Edwards Plateau is continuous along the southern border of the quadrangle, but erosion has dissected it until long fingers extend northward, the most important being between Mormon and Squaw Creeks and east of Squaw Creek. The geology of the Squaw Creek quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Kerrville quadrangle. Elevations ranging between 1,721 and 2,207 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, it is estimated that the relief within the quadrangle is about 620 feet, ranging between about 1,600 and 2,220 feet in elevation. The quadrangle is almost entirely within the Llano River drainage basin and is drained by Squaw Creek and Threadgill Creek and its tributaries Mormon and Dry Mormon Creeks. The water reaches Llano River by way of Beaver Creek. A small area in the northeastern corner of the quadrangle is drained by Pecan Spring Branch and reaches Llano River through Marshall Creek and Hickory Creek. An extremely small area in the southeastern corner of the quadrangle drains into Pecan Creek and reaches Pedernales River by way of Live Oak Creek. Squaw Creek quadrangle is high on the southern side of the Llano uplift, and rocks of Cambrian and Ordovician age outcrop in the northern part of the quadrangle. Faults in these rocks are related to the Ouachita orogeny. The Cretaceous rocks are essentially horizontal, dipping northward perhaps a few feet per mile. A small fault in the Cretaceous is exposed in a road cut 3 miles east of Doss. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region cannot be given in the space available. References cited below deal with some of these problems. This publication on the Squaw Creek quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to this index map to locate other quadrangles mentioned in the present text.
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    Geologic map of the Palo Alto Creek Quadrangle, Gillespie County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1952) Barnes, Virgil E. (Virgil Everett), 1903-1998
    Palo Alto Creek quadrangle is south of the Llano region and is in the marginal portion of the Edwards Plateau where much of the plateau surface has been destroyed by erosion. Along the northern edge of the quadrangle, a portion of a finger of the plateau trends eastward, and in the west-central part, another finger of the plateau frays out into a number of isolated outliers. The rest of the quadrangle is a portion of the gently undulating broad Pedernales River basin. The geology of the Palo Alto Creek quadrangle is shown on a planimetric map, and the only topographic map available is the reconnaissance 30-minute Fredericksburg quadrangle. Elevations ranging between 1,556 and 1,975 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, it is estimated that the relief within the quadrangle is about 550 feet, ranging between about 1,525 and 2,075 feet in elevation. The quadrangle is entirely within the Pedernales River drainage basin and is mostly drained by Palo Alto Creek and its tributaries. Barons Creek drains the southwestern corner of the quadrangle, and Willow Creek and the tributaries of North Grape Creek drain a small area in the northeastern corner. The Palo Alto Creek quadrangle is high on the southern side of the Llano uplift, and rocks from pre-Cambrian to Ordovician in age outcrop as inliers surrounded by Cretaceous rocks. The faulting accompanying the Ouachita orogeny (Barnes, 1948) is not exposed, but dips in Paleozoic rocks up to 9 are present. The Cretaceous rocks are essentially horizontal, dipping eastward about 8 feet per mile. Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region cannot be given in the space available. References cited below deal with some of these problems. This publication on the Palo Alto Creek quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to this index map to locate other quadrangles mentioned in the present text.
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    Gravity, magnetic, and generalized geologic map of the Van Horn -- Sierra Blanca Region, Trans-Pecos Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1972) Wiley, Michael Alan, 1935-
    The Van Horn-Sierra Blanca region lies athwart part of the boundary between two contrasting geologic provinces. The contrast between these two provinces, splendidly displayed by Holocene landforms in the present map area, has a history that dates back to at least Late Precambrian time. This remarkable contrast led R. T. Hill (1902) to suggest the possibility of a transcontinental fracture zone passing near Van Horn and along the boundary of the provinces. Later workers called Hill's frac ture zone the Texas lineament (Ransome, 1915) or the Texas direction of wrench faulting (Moody and Hill, 1956). Where it is exposed in the region, the Rim Rock fault (fig. 1) seems to form part of the boundary between the provinces. Numerous workers have suggested a long-enduring history of strike-slip movement along the Hillside fault (fig. 1). The Van Horn-Sierra Blanca region has been mapped in detail geologically, but because nearly half of the total area of the region is covered by late Cenozoic basin-fill and because subsurface control is sparse, it has not been possible to understand the region in detail in three dimensions. This report summarizes the methods and results of a ground magnetometer and gravimeter survey undertaken in an attempt to obtain a clearer understanding of the tectonic history of the region and of the structural significance of the Hillside and Rim Rock faults.
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    Geologic map of southern Quitman Mountains and vicinity, Hudspeth County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1970) Jones, Bill R.
    The Quitman Mountains are part of a narrow mountain range that extends southeastward from near Sierra Blanca, Texas (85 miles southeast of El Paso, Texas), into northern Mexico. The range is typical of many desert mountains of the southwestern United States in that it projects abruptly above the breached bolsons that border it. Thus, the Quitman Mountains stand in stark contrast topographically and geologically to the Hueco Bolson on the west and the Red Light Bolson on the east. Quitman Gap (also called Quitman Canyon, Quitman Pass, and Can de los Lamentos) divides the range into northern and southern parts. The northern Quitmans, composed of Tertiary intrusive and volcanic rocks with intensely folded Cretaceous rocks exposed around the periphery of the igneous mass, extend about 10 miles north-northwest from Quitman Gap to Interstate Highway 10. The southern Quitman Mountains, composed primarily of intensely folded and thrust-faulted Cretaceous rocks, extend from Quitman Gap south-southeast to the Rio Grande (a distance of about 25 miles). The elevation of the range gradually diminishes southward from about 6,600 feet above sea level in the northern part to slightly less than 4,000 feet above sea level near the Rio Grande. The maximum local difference in elevation is about 2,000 feet. The highlands of the area studied are horsts flanked by grabens that are partly filled with sediment eroded from the mountains to form intermontane basins. The block faulting that created the horst and graben system followed the igneous activity and was superimposed on the earlier Laramide folds, thrust faults, and strike-slip faults characteristic of the Chihuahua tectonic belt. The Cretaceous rocks exposed in the southern Quitman Mountains consist of about 14,000 feet of marine shale, sandstone, and limestone, and nonmarine sandstone and shale. The lower 3,000 to 4,000 feet of the sequence are nonmarine rocks. Volcanic rocks overlie truncated folds in the Cretaceous sequence and consist mostly of tuffs, welded tuffs, and andesite. The bolsons are filled by relatively undisturbed Tertiary and Quaternary sediments that were deposited as interbedded conglomerates and fine-grained lacustrine-playa deposits.
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    Geologic map of Bofecillos Mountains area, Trans-Pecos, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1970) McKnight, John F.
    The Bofecillos Mountains area of Trans-Pecos Texas contains a Tertiary volcanic vent and a varied sequence of lava flows, tuff, ash-flow tuff, and associated conglomerate, sandstone, and mudrock; after most of the volcanic activity had ceased, the area was block faulled and later dissected into a rugged high-standing terrain with striking exposures. The present study is a continuation of mapping in Trans-Pecos Texas supported by the Texas Geologic Atlas project of the Bureau of Economic Geology; emphasis in this report is placed primarily on thc volcanic stratigraphy and the structural and geomorphic evolution of these rocks to their present stage.
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    Geologic map of central Davis Mountains, Jeff Davis County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1968) Anderson, Jay Earl, Jr.
    The Davis Mountains are an erosional remnant of a volcanic field that probably covered 5 to 10 times their present areal extent of approximately 2,000 square miles. Many previous workers believed that much of the extrusive material in nearby parts of western Trans-Pecos Texas was erupted from the central Davis Mountains (Colton, 1957, p. 76; Lewis, 1949, p. 89; McAnulty, 1955, p. 54<3; Zabriskie, 1951, p. 36). To test this idea, petrologic, stratigraphic, and structural investigations were made in order to understand the relationships among the various extrusive and intrusive rocks in the central Davis Mountains. The Davis Mountains are located in Jeff Davis, Presidio, and Brewster counties in Trans-Pecos Texas; this report deals with about 24$0 square miles in the highest part of the range. Fort Davis is approximately 10 miles east of the southern part of the map area, and Marfa is about 18 miles south of the area. Ready access is provided by State Highways 166 and 118, Spur 78, several graded county roads, and numerous unimproved ranch roads. The Davis Mountains lie on the southeast end of the Diablo Platform of Permian age (King, 194,2, p. 665-666). The Diablo Platform is bounded on the northeast by the Delaware basin, and on the southwest by the Marfa basin. The central Davis Mountains consist of a series of sodarich, silicic pyroclastic units and lava flows of late Eocene to Oligocene age. The volcanic rocks were intruded by stocks, sills, and dikes, mostly in the same compositional range, during the latter part of the period of eruptive activity. Thirteen volcanic units, with an aggregate thickness of approximately 2,500 feet, and six intrusive units were mapped.