THE U1 II '·1'5 . Y DEPAR.1MENT OF GE AUSTIN 12, TE~ BUREAU OF ECONOMIC GEOLOGY THE UNIVERSITY OF TEXAS AUSTIN 12, TEXAS PETER T. FLAWN, Director ;;;;;;;;;;;;;;; !!!!!!!!!!!!!!! GEOLOGIC QUADRANGLE MAP NO. 25 ID =!!!!!!!!!!!!!!! 0.. 0 ;;;;;;;;;;;;;;; u ~ Ul 0.. - a- <( Geology of the Johnson City Quadrangle, r'- :E -;;;;;;;;;;;;;;; c:Q ..J 0 ~ ru w ru Cl Blanco County, Texas cQ -~ r-'l -;;;;;;;;;;;;;;; ,..,, 111 N ~ r-'l a BY ru Cl =!!!!!!!!!!!!!!! ..,. .... ;;;;;;;;;;;;;;; VIRGIL E. BARNES - 111u - .... - (') - ..,.0 !!!!!!!!!!!!!!! - Cl November 1963 THE UNIVERSITY OF TEXAS TO ACCOMPANY MAP-GEOLOGIC BUREAU OF ECONOMIC GEOLOGY QUADRANGLE MAP NO, 25 GEOLOGY OF THE JOHNSON CITY QUADRANGLE, BLANCO COUNTY, TEXAS VIRGIL E. BARNES CONTENTS Page Page General setting . ... ..... .. ........ ..... .................... .................................. 2 Trinity Group .................................................. ... ........ 6 Shingle Hills Formation .. ............. ................................. 6 Geologic formations ...... ... ................ ............................. ..... ........ 2 Hen sell Sand Member ............ ............. ...... ................. 6 Precambrian rocks ... .. ..... .. .... ...... .. ... ................... ......... .. .. .. ... .. 2 Glen Rose Limestone Member ...... ................... ....... 6 Igneous rocks ..... ........................................................... .......... 2 Fredericksburg Group ....................... .............................. 7 Town Mountain Granite .............................. ..................... 2 Walnut Clay ................................................................ 7 Paleozoic rocks ............................................................................ 2 Comanche Peak Limestone ................. ...................... .... 7 Cambrian System (Middle and Upper Cambrian) .......... 2 Cenozoic rocks .......... ............................................................. 7 Riley Formation ....................................................... 2 Quaternary System ...................... .................................... 7 Hickory Sandstone Member ............ ...................... 2 Recent Series .. ............ ................... ... ............................ ... 7 Cap Mountain Limestone Member ...... ....................... 3 Alluvium .......................................................... 7 Lion Mountain Sandstone Member ............................ 3 Wilberns Formation ...................................... .... ...... ........ 3 Subsurface geology ..................................................... 7 W elge Sandstone Member ... .. ................ ........ ............ .. 3 Mineral resources ....................................... ................. 8 Morgan Creek Limestone Member .. .... .. .................. 3 Construction materials ..................................... .... ................ .. 8 Point Peak Member ............................... ...................... 4 Dimension stone . ......... ...................... 8 San Saba Member .... ............... .... ... .. ......... .. .. ...... .... 4 Crushed stone ....... .................. .............. ... ........................ ... 8 Ordovician System (Lower Ordovician) ............. 5 Sand and gravel ..... ... ................................. ............... ... .. 8 Ellenburger Group .. .......................................... .. ... ....... .. 5 Road material .......... ................................. ............................ 8 Tanyard Formation ......... .. .......... ..... ..................... 5 Lead and zinc . .. ... ................................. .. .. .... ... ......... ... .............. 8 Threadgill Member ................................................ 5 Water ............................................... ........................................ 8 Staendebach Member . ............................................. 5 References ... ....... .... ........ ... ................. ................... ....... ....... .... ......... 9 Gorman Formation ...... .................................................. 6 Honeycut Formation . .................................................... 6 Sample description .............................................. .. .......................... 10 Mesozoic rocks ............. ................... ................... ..................... 6 Winans and Forbes No. 1 Buckner well ..... .................... 10 Cretaceous System (Lower Cretaceous ).......................... .... 6 Stratoray Oil Corporation No. 1 Stribling well ............. 10 2 Bureau of Economic Geology, The University of Texas GENERAL SETI'ING Johnson 'City quadrangle is entirely Russell, Cottonwood, Salter Spring, Tow­ in cited references. This publication on within the Pedernales 'River basin in the head, Flat, Town, and Deer creeks and the Johnson City quadrangle is the first southeastern part of the Llano region. other unnamed drainages. of a series of central Texas geologic Although there are remnants of the Ed­ Johnson City quadrangle is high on quadrangle maps which will be compiled wards Plateau in adjacent quadrangles, the southeastern side of the Llano uplift. as topographic bases become available. within this quadrangle only Buffalo Peak Precambrian, Cambrian, and Ordovician An index map for geologic maps already reaches nearly to the plateau level. rocks crop out in about two-thirds of the published on planimetric bases and The geology of the Johnson City quad­ quadrangle; Cretaceous rocks and some others planned for publication on the rangle is shown on a U:S. Geological Quaternary surficial deposits occupy the new topographic bases is shown with the Survey 7% minute topographic quad­ remainder. Faults related to the Oua­ geologic map. rangle map-contour interval 20 feet, chita structural belt trend mostly in The eastern two-thirds of the Johnson scale 1 :24,000. The relief in the quad­ northeastward-southwestward directions City quadrangle, mapped geologically in rangle is about 610 feet; elevations range ranging from almost north-south to al­ 1942 and '1943 by the writer and L. E. from about 1,050 feet where Pedernales most east-west. Paleozoic rocks mostly Warren, was published as part of a River leaves the quadrangle to slightly dip southeastward at angles up to about planimetric map (Cloud and Barnes, more than 1,660 feet at the top of Buf­ 10 degrees, and the relatively flat-lying 1948, Pl. 3). With the assistance of L. E. falo Peak. Cretaceous rocks dip eastward about 12 Warren and A. R. Palmer, the rest of The quadrangle is drained by Peder­ feet per mile. the area was mapped geologically and a nales River and its tributaries-North Discussions of stratigraphy, structural, gravity survey completed by 1948. Grape, 'Spring, Hickory, Buffalo, Hardin economic, and geophysical problems are GEOLOGIC FORMATIONS PRECAMBRIAN ROCKS terized by gravity minima, this buried PALEOZOIC ROCKS IGNEOUS ROCKS hill may be a phase within the Town CAMBRIAN SYSTEM (MIDDLE AND Town Mountain Granite Mountain Granite rather than Oatman UPPER CAMBRIAN) Town Mountain 'Granite belonging to Creek Granite. Oatman Creek Granite Riley Formation the Grape 'Creek granite mass ('Barnes, in the Llano region occurs in separate Hickory Sandstone Member.-The Dawson, and Parkinson, 1947, p. 45) bodies and in bodies adjacent to Town 'Hickory 'Sandstone crops out in five fault crops out in several places along the Mountain Granite masses but is unknown blocks in the northwestern part of the western edge of the quadrangle and within a Town Mountain Granite mass. Johnson City quadrangle. In thickness along Hickory Creek. The two north­ The grain size of this granite is larger and appearance it resembles the Hickory westernmost outcrops are separated by than normal for Oatman Creek Granite Sandstone described in the White Creek a graben of Hickory Sandstone and some and the granite lacks cataclastic texture, section of Blowout quadrangle (Barnes, of the outcrops to the south are buried a common characteristic of Oatman 1952a) where it is 276 feet thick. Wise hills that perhaps reached as high as the Creek Granite. (MS.) found no measurable section ex­ base of the Cap Mountain Limestone As described by Barnes, Dawson, and posing the entire thickness of the sand­ before the Cap Mountain was eroded. Parkinson (1947, pp. 51-52), the granite stone. He estimated that about 150 feet The granite is light pink, coarse has an average grain size of 10 mm, is of the lower part is exposed half a mile grained, somewhat porphyritic, and com­ brownish tinged with red and yellowish north of Sandy. posed mostly of microcline, quartz, green, and takes an exceptionally bril­ In its lower part the Hickory is mas­ plagioclase, and some biotite. Accessory liant polish. It is composed mostly of sive, cross-bedded, coarse grained, and minerals are magnetite, fluorite, apatite, microperthite and quartz with lesser in places near its base contains micro­ titanite, and zircon. The granite contains amounts of hornblende and biotite. Pla­ cline granules and conglomerate lenses. a few small pegmatites, aplite bodies, gioclase is very scarce and is present as In its middle part beds are thinner and and quartz veins. crystals associated with the femic min­ cross-bedding is on a smaller scale. In its A Town Mountain (?) Granite dome erals. Accessory minerals are magnetite, upper part clay and silt are abundant; exhumed by Pedernales River extends apatite, and zircon. topographically this unit forms a soil­