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

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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 into the North Grape Creek quadrangle This buried granite hill, before it was covered bench. The sand in the Hickory (Barnes, 1952b), where it is designated exposed and eroded, may have reached is poorly sorted, mostly angular to sub­ as Oatman Creek Granite. Evidence almost to the base of the Lion Mountain rounded, and most grains have rough favors assigning this outcrop to the Town Sandstone. Quaquaversal dips in the Cap surfaces. Mountain Granite. A gravity survey by Mountain Limestone adjacent to the The Hickory Sandstone supports de­ Barnes, Romberg, and Anderson ( 1954a, granite are interpreted as due to intra­ ciduous trees, prominent among which 1954b, 1955) shows this outcrop to be in stratal solution, evidenced by abundant are the broad-leaf oaks, in contrast to the a gravity minimum associated with the stylolites. The contact of the granite and overlying Cap Mountain Limestone Grape Creek granite mass. As Town limestone is well exposed east of Peder­ which supports cedar, live-oak, and an Mountain Granite masses are charac- nales River. assortment of daggers and cacti. Geology of the Johnson City Quadrangle, Blanco County, Texas 3

Trilobites collected by Palmer ( 1954) is fine- to medium-grained, yellowish­ gray where shaly and grayish olive green from locality 6-9A are Bolaspidella pro­ gray to greenish-gray, sparsely to very where composed of glauconite. The white oculis and Modocia cf. M. oweni and glauconitic dolomite and limestone con­ limestone is a trilobite coquinite, and from locality 6-20A, Baltagnostus cf. B. taining a few trilobites, with a 3-foot bed trilobites and phosphatic brachiopods centerensis, Bolaspidella prooculis, and of siltstone at the top. The remaining 21 including acrotretids are common in the Modocia cf. M. oweni. The locality data feet of rock is mostly coarse-grained, rest of the rock. The next 10 feet is given by Palmer are in error-locality coarsely glauconitic, trilobitic limestone, mostly medium-grained, grayish olive­ 6-9A is 0.8 mile airline east-northeast of except for one 3-foot interval which is a green greensand composed of glauconite, Sandy, not just south as stated; and coquinite of phosphatic brachiopods. a minor amount of shale, and a few thin locality 6-20A is 1.7 miles airline due Brachiopods collected by Palmer cross-beds of trilobite coquinite lime­ south of Sandy, not just west as stated. (1954, p. 786) from locality 6-lOA are stone. The top 2 feet of the Lion Moun­ Fossils at locality 6-lOB are linguloid Angulotreta postapicalis. The locality tain is much weathered, moderate olive­ brachiopods. data given by Palmer are in error­ brown, glauconitic shale. Wise (MS.) found 5 species of trilo­ locality 6-lOA is 1.0 mile due east of Fossils collected at localities 6-24A and bites and 1 species of phosphatic brach­ Sandy, not south as stated. 6-24B are phosphatic brachiopods. Wise iopod in the Bolaspidella zone, which is Wise (MS.) collected fossils from (MS.) identified 9 species of trilobites mostly in the upper part of the Hickory three zones in the Cap Mountain; the and 2 species of phosphatic brachiopods Sandstone in this area. number of species identified are listed in the Aphelaspis zone, which is essen­ tially coextensive with the Lion Moun­ Cap Mountai~ Limestone Member.­ in table l. Outcrops consist of a narrow graben west tain Sandstone Member. TABLE 1 of Sandy, a semicircular exposure Wilberns Formation around the exhumed granite dome on Number ot species of fouih Welge Sandstone Member.- The very Pedernales River, and, in the north­ Mi11cel· narrow Welge Sandstone outcrop forms western part of the quadrangle, a 1.5- Brach· laneous a scarp parallel to the Lion Mountain mile wide northeast-southwest-trending iopods, and Trilo- phos- undeter· Sandstone bench in the northwestern belt o!Iset by the Hogthief Bend fault. Zone bites pbatic mined part of the quadrangle and encircling The entire sequence is exposed along Coosina 12 1 3 the exhumed granite dome on Peder­ Hickory Creek and Pedernales River and Coosella .. ... 14 3 0 nales River. Another small exposure likewise on the opposite side of the fault Cedarina-Cedaria ...... 5 2 1 south of the main outcrop is along a along North Grape Greek and Peder­ fault. In the Klett-Walker section nales River. Lion Mountain Sandstone Member.­ (Barnes, 1956, p. 56) the Welge is 12 The Cap Mountain Limestone is simi­ The Lion Mountain Sandstone also en­ feet thick. It is coarse-grained, dark lar to that described in the White Creek circles the exhumed granite dome along yellowish-brown to pale yellowish-brown, section of Blowout quadrangle (Barnes, Pedernales River and in the northwest­ cross-bedded quartz sandstone; locally it 1952a); Wise (MS.) estimated that the ern part of the quadrangle forms a nar­ is quartzite. In sunlight the rock glitters Cap Mountain is slightly less than 500 row northeast-southwest-trending outcrop as light is reflected from secondary crys­ feet thick. He measured and described interrupted by faults. The rocks weather tal faces. 'Beds range from 4 inches to 407 feet of the upper and lower parts of to a bench 400 to 500 feet wide with 4 feet in thickness; glauconite and shaly the member in his Hickory Creek sec­ widely scattered live-oak mottes. The beds are scarce. Elsewhere in the Johnson tion, and the lower 59 feet is again only rock normally exposed is fragments City quadrangle the basal bed contains described in his Sandy Post-office section. of trilobite coquinite. The bench is dis­ 0.25- to 0.5-inch quartz pebbles but none The lower part of the Cap Mountain, tinctly visible on aerial photographs. this large were seen in the line of section. mostly calcareous sandstone and sandy In the Klett;Walker section (Barnes, Wise (MS.) measured 6 feet of Welge limestone, forms a scarp above the soil­ 1956, p. 56) the Lion Mountain is 31 feet Sandstone in the Gipson ranch section eovered Hickory 'Sandstone bench. Up­ thick, which is less than its normal thick­ and noted that in this section it is very ward, sand is less abundant and the ness in the Llano region. Wise (MS.) glauconitic. He stated that within his middle part of the member is a dis­ found the Lion Mountain to be 42 feet map area the Welge is coarser at the tinctly jointed, relatively pure, massive thick in the Gipson ranch section and base. limestone. The joints have been widened 46 feet thick in the nearby Hickory Creek Trilobites were first collected from the by solution and show clearly on aerial section. The thinness of the Lion Moun­ basal part of the Welge sandstone in the photographs. tain in the Klett-Walker section may in Llano region near the mouth of Buffalo The upper 98 feet of the member is part be the result of restricted sedimen­ Creek by Leo Hendricks, of Texas described by Barnes (1956, p. 57) in the tation over the buried granite dome and Christian University. Josiah Bridge of Klett-Walker section, which extends to some extent due to southward regional the U .'S. Geological Survey recognized southward from the exhumed granite thinning. The bottom 2-foot bed in the that these trilobites were related to some dome along Pedernales River. In this Klett-Walker section is very fine-grained in the Morgan Creek Limestone, thus section the lower 53 feet of rock is fine­ glauconitic sandstone followed by 17 feet furnishing the first paleontological evi­ grained, mottled weathering, greenish­ of coarse-grained, slightly sandy, mostly dence for placing the Welge in the Wil­ gray to yellowish-gray, slightly glauco­ cross-bedded, variably glauconitic, light berns Formation rather than in the Riley nitic, massively bedded dolomite con­ olive-gray to greenish-gray and dark Formation. taining sporadically distributed crystals greenish-gray to off-white limestone and Morgan Creek Limestone Member.­ of galena. The overlying 24 feet of rock greensand. The greensand is light olive Morgan Creek Limestone encircles the Bureau of Ecorwmic Geology, The University of Texas exhumed granite dome on Pedemales TABLE 2 northeast-southwest-trending outcrop belt River and extends northeastward across passing through the center of the John­ one small fault to where it is overlapped Number of llpecies of foasih son City quadrangle. Another outcrop by Cretaceous rocks. From here to the Mi11cel· of the lower part of the member is in laneou11 northeastern comer of the quadrangle Bracbiopod1 and Hogthief Bend along the northwest side it crops out only along creeks. Another Phoa- Cal- unde- of the Hogthief Bend fault. Zone Trilobite• pbatie cilic termined outcrop is in Hogthief Bend where the Barnes (Cloud and Barnes, 1948, pp. rocks are down-dropped to the northwest Ptychaspi-s- 341-342, Pis. 3, 12) measured 195 feet Prosaukia ...... 11 1 1 1 along the Hogthief Bend fault. Conaspis ...... 8 3 5 1 of San Saba Member beds ("Pedernales In the Klett-Walker section (Barnes, Elvinia ...... 23 1 0 0 Dolomite") in the upstream Pedernales 1956, pp. 54-56) the Morgan Creek Dunderbergia .... 4 1 0 0 River section. About 3 miles to the north­ Limestone is 126 feet thick, and in the east, the Stratoray Oil Corporation No. Gipson ranch section (Wise, M'S.) it is Creek Limestone and crops out south­ 1 Stribling well (completed in 1955) reported to be 149 feet thick. In the east of it. In both the Klett-Walker sec­ penetrated 310 feet of 'San Saba beds. Klett-Walker section, the lower 18 feet is tion (Barnes, 1956, p. 54) and the Gip­ The outcrop pattern in the vicinity of thick bedded, stylolitic, coarse grained, son ranch section (Wise, MS.), it is 25 the well indicates that as much as 130 massive, glauconitic and in part oolitic, feet thick. These are by far the thinnest feet of higher San Saba beds are also ranging from a calcareous sandstone at sections of Point Peak measured in the present in this area so that total esti­ the base to a slightly sandy limestone at Llano region. mated thickness is 440 feet. This is more the top. It is mostly pale yellowish brown The Point Peak is mostly fine-grained, than twice the thickness measured in the and grayish orange pink, along with silty, thin-bedded (0.25 to 0.5 inch, max­ upstream Pedernales River section. It some pale red and light olive gray, imum 3 inches), greenish-gray limestone seems clear that in the measured section whereas elsewhere in the Llano region containing thin beds of intraformational a fault cuts out about 250 feet of the this part of the Morgan Creek is pale conglomerate and two stromatolite zones uppermost 'San Saba beds. The thickness red or even deeper red. Some of the ooids each about 2 feet thick. The upper two estimate of 440 feet is supported by an are dolomitized and much of the lime­ feet of the member is thin-bedded, silty even thicker section of San Saba beds stone is composed of fossil fragments. dolomite containing a 4-inch, oolitic, found to the south in the Roland K. Identifiable fossils are scarce. cherty bed. Blumberg No. 1 Wagner well (Barnes, The upper 108 feet of the Morgan The rapid southward thinning of the 1959, Pis. 1, 3). Creek is composed of alternating beds Point Peak in Blanco County appears Of the lower 121 feet of San Saba beds of fine-grained and coarse-grained lime­ to be the result of either (1) gradation measured in the Klett-Walker section stone formed mostly of organic debris. of silty Point Peak sediment laterally (Barnes, 1956, pp. 53-54), the lower 87 Aphanitic to microgranular stromatolites to dolomite of the San Saba Member, feet is fine•grained, yellowish-gray, are common in the upper part. Colors or ( 2) cutting off of the silt supply by medium-bedded (6-12 inches) dolomite are varied, commonly medium gray to a stromatolitic reef, resulting in a rela­ containing one 8-foot and one 4-Ioot greenish gray, yellowish gray, brownish tively thin accumulation of silty sedi­ oolitic zone. The upper 34 feet is coarse­ gray, light olive gray, and dark yellowish ment south of the reef. grained, light yellowish-gray, massive dolomite which weathers into rounded, orange where dolomitic. Glauconite is San Saba Member.-Subsequent to solution-pitted, boulder-like masses. sparse to very abundant; fine grained in publications on the '.Blowout quadrangle In the upstream Pedernales River sec­ the fine-grained silty beds and commonly (Barnes, 1952a) and the North Grape tion the lower 86 feet of the 'San 'Saba coarse grained in the coarse-grained Creek quadrangle (Barnes, 1952b)­ is fine-grained dolomite similar to that beds. both adjoining the Johnson City quad­ in the Klett-Walker section, except that Fossils in the Morgan Creek Lime­ rangle-Barnes and Bell (1954) pro­ the upper 15 feet contains dirty white stone include numerous trilobites, phos­ posed a change in nomenclature to bring to rusty, porous to compact, fossiliferous phatic brachiopods, and in the upper Wilberns terminology into conformity quartzose chert (Joe. 6-5A). The over­ two-thirds numerous calcitic brachiopods, with Ellenburger terminology. The lying 104 feet is massive, coarse-grained, some of which are silicified toward the names "Pedernales Dolomite" and "San light gray and pinkish-gray dolomite top of the member. Bell and Ellinwood Saba Limestone" on the map and in the with some dull dark reddish-purple mot­ (1962) illustrated and described a few text of North Grape Creek quadrangle tles. Somewhere in this sequence, per­ fossils from the Klett-Walker section and are no longer used. Instead these rocks haps near the top as judged from com­ Barnes and Bell (MS.) made fauna! are included in the San 'Saba-the top parison with the section in the Stratoray lists. Additional collections of brachio­ member of the Wilberns Formation. Oil Corporation No. 1 'Stribling, is the pods made from localities 6-23A, 6-24C, Where dolomite and limestone are fault that cuts out an estimated 250 feet and 6-24D are in part silicified. mapped separately, they are shown as of section. The dolomite in the well cor­ Numerous fossil collections made by dolomitic and calcitic facies of the San Wise (MS.) from four zones in the Saba Member. They are comparable in responding to the faulted-out part of the lower half of the Wilbems Formation rank to the dolomitic and calcitic facies upstream Pedernales River section is are mostly from the Morgan Creek mapped in the overlying Threadgill mostly fine and very fine grained. The Limestone. The number of species iden­ Member and other units of the Ellen­ top 5 feet of the San Saba in this section tified are listed in table 2. burger Group. is medium gray to yellowish-gray, micro­ Point Peak Member.-The Point Peak The San 'Saba Member, where not con­ granular dolomite. Member is coextensive with the Morgan cealed by Cretaceous rocks, forms a wide In the southwestern part of the quad- Geology of the Johnson City Quadrangle, Blanco County, Texas 5 rangle, the upper part of the San Saba of the quadrangle, and the third north The 50 feet of Staendebach described is fine-grained dolomite; lateral inter­ of U.S. Highway 290 west of Towhead in the Towhead Creek section is dolo­ gradation of fine- and coarse-grained Creek. The latter is a small outcrop. It mite, in part fine grained and in part dolomite has been mapped. Also in this is probably Threadgill but the possibility medium to coarse grained, mostly light area the San Saha Member contains a of its being San Saba or Staendebach gray with a pinkish cast, medium few masses of white, aphanitic limestone must not be ruled out. bedded, and somewhat cherty. The which grades into coarse-grained dolo­ In the Johnson City area, the Thread­ Staendebach in the downstream Peder­ mite. gill Member is 242 feet thick (Cloud and nales River section is mostly medium­ Fossils from six collections in the San Barnes, 1948, pp. 312, 339-341) and to thick-bedded dolomite. The lower 200 Saba Member were identified by P. E. mostly coarse-grained, light gray dolo­ feet is mostly fine to medium grained, Cloud, Jr., U.S. Geological Survey, and mite, except between Pedernales River contains some fine- to very fine-grained W. C. Bell, Department of Geology, The and Towhead Creek where 182 feet of dolomite, and ranges in color from yel­ University of Texas, as follows: white to light gray, aphanitic limestone lowish gray to medium gray and brown­ was measured. This limestone body inter­ ish gray. The upper 165 feet is mostly LOCALITY FOSSILS grades laterally with coarse-grained dol­ light gray to yellowish-gray, medium­ 2-46B Finkelnburgia sp. omite, the dominant Threadgill rock type grained dolomite. Chert, characteristic Scaevogyra cf. swezeyi Whitfield in this part of the Llano region. Similar of the Staendebach, is mostly porcelan­ 2-56A Plectotrophia cf. P. bridgei Ul­ intergradation of limestone and dolomite eous, white to off-white, dolomoldic to rich & Cooper 2-57C Finkelnburgia sp. was mapped in the southwestern part of compact, in part oolitic, and near the top Schizo pea cf. elevata (Ulrich the quadrangle. of the section (Joe. 2-59A) very fossili­ and Bridge) 1"ossils collected from quartzose chert ferous. (See Cloud and Barnes, 1948, Dirhachopea cf. D. normalis Ul­ in the Threadgill Member were identi· p. 337, for fauna! list.) rich and Bridge Sinuopea spp. fied by P. E. Cloud, Jr., U. S. Geological Eleven other fossil collections made New cyrtocarinate ecculiompha­ Survey, as follows: from Staendebach rocks have been iden­ lid gastropod genus tified by W. C. Bell, Department of Ge­ Stenopilus sp. LOCALITY FOSSILS ology, The University of Texas, P. E. Saukiinid trilobite 6-3A Scaevogyra cf. S. swezeyi Whit­ 6-5C Sinuopea sp. Cloud, Jr., U. S. Geological Survey, and Ozarkina sp. R. H. Flower, New Mexico Institute of field Ophileta sp. Plethometopus sp. Schizo pea (?) Mining and Technology, as follows: 6-4A X enorthis sp. 6-5D Sinuopea (?) Anconochilus barnesi Knight Schizopea (?) LOCALITY FOSSILS Hypseloconus sp. Trilobite 2-57A Ophileta sp. Plethopeltis (?) 6-5F Euconia (?) Unidentified trilobites Gasconadia cf. G. putilla (Sarde­ Ectenoceras (?) son) 6-5G Cf. Finkelnburgia High-spired Ophileta sp. Dirhachopea sp. Schizopea grandis (Ulrich & Bridge) Cf. Hypseloconus The Staendebach Ophileta in chert New genera aff. Ecculiomphalus Hydrozoan? or trepostomatous from locality 6-5F must be float from bryozoan? Inadvertently, Barnes (Cloud and nearby Cretaceous conglomerate. Sinuopea regalis 'Butts Barnes, 1948, p. 342) listed locality Staendebach Member.-The outcrop 2-57B Ozarkina sp. 6-4A as locality 2-4A. Finkelnburgia (?) belt of the Staendebach Member, inter­ Trilobite rupted by faults and Cretaceous cover, 2-58B Cf. Gasconadia putilla (Sarde- OllDOVICIAN SYSTEM (LOWER extends from a point 1 mile north of son) ( ?) ORDOVICIAN) Johnson City in a north-northeast direc­ Roubidouxia sp. Hystricurus sp. ELLENBURCEa Gaour tion for a distance of 4 miles and west­ Tunyard Formation Nautiloid(?) ward from the same point for a distance Ophileta sp. Threadgill Member.-In the Johnson of 3 miles. The westernmost outcrops 2·580 Fragmentary gastropods City area the position of the San Saba­ are inliers surrounded by Cretaceous Brevicone cephalopods Threadgill boundary in reference to the 6-5A "Helicotoma"(?) rocks. Ophileta sp. position of the Cambrian-Ordovician In the Johnson City quadrangle the Gasconadia sp. boundary is unknown because of lack of Staendebach Member is mostly dolomite Dalceoceras sp. paleontologic evidence. The uppermost but some limestone occurs in the west. Clarkeoceras sp. part of the San Saba could be Ordovician Caseoceras (?) Cloud and Barnes (1948, pp. 312-313, Conocerina sp. or the lower part of the Threadgill could 337-339) included in the Staendebach 6-5B Ophileta sp. be Cambrian. The boundary between the the upper 50 feet of rock in the Towhead Sinuopea cf. humerosa Butts members, where in dolomite, is placed Creek section and the lower 365 feet of 6-6A Ophiletg sp. at the top of the fine-grained dolomite rock in the downstream Pedernales River Ozarkina typica Ulrich & Bridge above the highest Cambrian fossils and Gasconadia putilla ( Sardeson) section. These two sections, comprising Sinuopea cf. S. humerosa Butts at the bottom of coarse-grained dolomite 415 feet of rock, are believed to account Schizopea grandis (Ulrich & below the lowest Ordovician fossils. for all of the Staendebach Member in Bridge) The Threadgill Member crops out in this area. The same thickness of Staende­ Cystid plates Clarkeoceras ( ? ) three areas, one along Pedernales River bach was penetrated in the Roland K. 6-6B Ophileta sp. north-northwest of Johnson City, one Blumberg No. 1 Wagner well to the Helicotoma (?) along the edge of the southwestern part south (Barnes, 1959, Pis. 1, 3). Lytos pira ( ? ) 6 Bureau of Economic Geology, The University of Texas

Gasconadia cf. G. putilla (Sarde· chert is common. Dolomite, especially southeastern part of the quadrangle son) where fine to medium grained, com· where it may be as much as 100 feet Silluopea sp. Trilobite monly grades laterally to limestone and thick in the southern reach of the 6-6C Ozarkina sp. vice versa. No two sections have the same Hensell-filled channel that crosses Peder· 6-14A Lytospira sp. proportion of limestone and dolomite. nales River east of Johnson City. Conocerina, n. sp. Likewise, the Gorman rocks in the John­ A large area of conglomerate is 6-15A Helicotoma uniangulata (Hall) Lytospira sp. son City quadrangle do not have the mapped at the base of the Hensel! north· Ophileta sp. same proportion of limestone and dolo­ west of Johnson City and conglomerate, Ozarkina typica Ulrich & Bridge mite as in the upstream Honeycut Bend not separately mapped, occupies much Ozarkina complanata Ulrich & section although the same rock types are of the Hensell-filled channel crossing Bridge Sinuopea sp. present. Pedernales River. In general, the Hen­ Paraplethopeltis sp. Fossils collected from the Gorman sell becomes finer grained upward rang­ Ectenoceras sp. Formation were identified by P. E. ing from conglomerate in places at the Cloud, Jr., U.S. Geological Survey, as base to abundant silt and clay in the Gorman fossils present in the collec­ follows: upper part; however, tongues of coarser tion from locality 2-58B are float from grained material commonly occur at Gorman rocks east of the nearby fault. LOCALITY FOSSILS various levels depending to some extent & Gorman Formation 2-58C Rhombella umbilicata (Ulrich on the nearness laterally of pre-Creta· Bridge) ceous rocks. The kind of pre-Cretaceous The Gorman Formation in the John­ Ophileta rock from which the Hensell is derived son City quadrangle is represented by a 2-59B Lecanospira influences its composition and character. lower dolomitic facies and an upper cal­ 2-59C Rhombella umbilicata (Ulrich & Bridge) The lower part of the Hensel! is mostly citic facies. The dolomitic facies crops red, other colors are common, and up­ out (1) 2.5 miles northeast of Johnson Honeycut Formation ward the reds give way to various shades City along Pedernales River, (2) in a The Honeycut Formation crops out in of gray, yellowish gray and greenish graben 3 miles north-northeast of John­ two areas about 2 miles east from John­ gray. son City, and (3) at the edge of over· son City, one along Pedernales River Within the Johnson City quadrangle, lapping Cretaceous rocks in two other and the other north of the road to Honey· the vegetation on the Hensell is similar areas, one just north and one 2 miles cut Bend. Not more than 50 to 100 feet to that on the overlying Glen Rose, indi­ west-northwest of Johnson City. Calcitic of the lower part of the formation is cating that much calcareous material is Gorman crops out south of the dolomitic present. The rocks exposed are alternat· present perhaps both as caliche and de· Gorman in the fault blocks north-north· ing beds of light to medium gray apha· trital limestone derived from Paleozoic east and northeast of Johnson City and nitic limestone and light to medium rocks. Johnson City and most of the in the latter extends south of the road gray to yellowish-gray, microgranular to cultivated land within the quadrangle leading eastward to Honeycut Bend. The fine-grained dolomite. Some beds are are on Hensel! outcrop. boundary between the two facies is coin­ slightly sandy, some are cherty, and all cident with the Archaeoscyphia bed are well exposed along Pedernales River, Glen Rose Limestone Member.-The where found; elsewhere it divides rock where at the point on the map marked Glen Rose Limestone crops out mostly that is predominantly limestone from "F" the basal bed of the Honeycut For­ in the northeastern and southern parts rock that is predominantly dolomite. mation contains numerous Xenelasma. of the Johnson City quadrangle. It rests The lower 14 feet of the Gorman dolo­ Fossils from locality 2-60C near the directly on Paleozoic rocks in the north· mitic facies, described by Cloud and base of the Honeycut were identified western part of the quadrangle and lo­ Barnes ( 1948, p. 337) in the downstream by P. E. Cloud, Jr., U. S. Geological cally in the northeastern, southwestern, Pedernales River section, is mostly mi· SurYey, as 3 species of Jeffersonia and and southeastern parts of the quadrangle. crogranular, in part sandy, and cherty. gastropods. The Glen Rose may be as much as All of the Gorman Formation has been 260 feet thick in the Johnson City quad­ described (Cloud and Barnes, 1948, pp. MESOZOIC ROCKS rangle in the vicinity of Buffalo Peak. It consists of alternating beds of limestone, 331-336) in the upstream Honeycut CRETACEOUS SYSTEM (LOWER dolomite, clay, silt, and sand or, more Bend section, 2 miles east of the John­ CRETACEOUS) precisely, beds com posed of various pro· son City quadrangle, where the dolomitic TRINITY GROUP portions and combinations of these ma· facies is 246 feet thick and the calcitic Shingle Hills Formation terials. The beds vary in their resistance facies 244 feet thick. Here the boundary Hensell Sand Member.-The Hensell to erosion, producing a "stair-step" to­ is 10 feet beneath the Archaeoscyphia Member (Barnes, 1948) rests on an ir· pography. The less easily eroded beds bed. In this section 23 feet of limestone regular erosional surface carved on and 223 feet of dolomite comprise the Paleozoic rocks ranging in age from of limestone, dolomite, and, locally in its lower part, calcite-cemented sand­ dolomitic facies, and of the dolomite, Cambrian Morgan Creek Limestone to stone, form the tread of the steps and the 174 feet is microgranular and 49 feet Ordovician Honeycut rocks. Northwest­ is mostly fine grained. The calcitic facies ward it laps out against the erosion sur· softer less resistant zones between form is almost half dolomite, of which about face, and ridges and hills of Paleozoic the risers. 85 feet is microgranular and the rest rock in several places in the northern The base of the Glen Rose Limestone mostly fine grained. Throughout this sec­ and western parts of the quadrangle in· is placed at the base of the lowest scarp· tion the limestone is aphanitic, slightly terrupt the continuity of the Hensell forming bed. In tracing the contact west· sandy beds occur at many levels, and outcrop. The Hensell is thickest in the ward, as scarp-forming beds fade, the Geology of the Johnson City Quadrangle, Blanco County, Texas 7

contact rises to the base of the next surface of the Paleozoic sequence. in other adjacent quadrangles, the lime· higher scarp-forming bed. Most of this The Glen Rose is mostly suited to stone is argillaceous and soft. contact was traced between observed ranching, although flatter areas in the CENOZOIC ROCKS points with the aid of a stereoscope. lower part are cultivated. In general, the QUATERNARY SYSTEM Gulf ward frem the Johnson City quad· vegetation on the Glen Rose is spa1·ser Recent SerJes rangle, a thin fossiliferous zone near the than on other units, indicating the rela· Alluvium.-Deposits of alluvium oc· middle of the Glen Rose has been called tive sterility of its soil. cur mostly along Town, Flat, and Tow· the Salenia texana zone (George, 1947, head creeks, and Pedemales River. Large p. 17; and Whitney, 1952, p. 66). The FaEDEIUCKSBtJ&G Gaour pecan trees grew in the alluvium along top of this zone is characterized by a Walnut Clay.-Walnut Clay contain· Pedernales River at the time the area bed containing Corbula. Within the ing abundant Exogyra crops out in the was mapped, but in 1952 most of the quadrangle Salenia texana was not found northern part of the quadrangle near the pecan trees were destroyed by a record­ and the Corbula bed is poorly developed. top of Buffalo Peak. Its outcrop width breaking flood, which also carried away It has been mapped where present, and is so narrow that it is represented on the much of the alluvium. Narrow belts and map by a line and its thickness is prob· westward in the northern part of the patches of alluvium follow some of the quadrangle where it can no longer be ably less than 5 feet. lesser drainages but are insignificant found, the approximate horizon of Cor· Comanche Peak Limestone.-The and have not been mapped. Most of the bula was traced with the aid of a stereo· lower part of the Comanche Peak Lime­ alluvium along Town, Towhead, and Flat scope to its intersection with the eroded stone forms the top of Buffalo Peak. As creeks is cultivated.

SUBSURFACE GEOLOGY

Two-thirds of the surface area of the Johnson City, samples are few; however, Creek granite mass (fig. 1). Johnson City quadrangle is formed by the following units can be identified: The rocks which cause the fairly weak Paleozoic rocks. All units of the Cam· gravity maximum and fairly strong mag­ brian and Lower Ordovician are repre­ Gorman Formation-dolomitic facies Tanyard Formation netic maximum in the southeastern part sented, and these same units occur be· Staendebach Member-dolomitic fa. of the quadrangle are not known. How­ neath the Cretaceous rocks of the quad­ cies ever, similar-strength magnetic maxima rangle. Two wells spudded in Cretaceous Threadgill Member-dolomitic fa. in the Fredericksburg area are associated rocks were drilled through the Creta· cies with diorite, and the broad gravity max· ceous into Paleozoic rocks, and one, the Wilberns Formation imum could be produced by Packsaddle Stratoray Oil Corporation No. 1 Stribling San Saba Member- dolomitic and schist. about 4.5 miles north-northeast of John· calcitic facies son City, bottomed in Precambrian 'Sources of in formation about the Pre· coarse-grained Town Mountain Granite. cambrian rocks upon which the Paleozoic This well penetrated the following units: rocks lie are limited to outcrops of granite in the western part of the quad· Thickneu Depth. Stratisraphic unit in feet in feet rangle, granite in the Stratoray Oil Cor­ poration No. 1 Stribling, and to gravity Cretaceous Heosell Sand 70 0- 70 and magnetic data (fig. 1). The gravity Cambrian data show a gravity minimum in the Wilbern1 Formation 485 70- 555 western part of the quadrangle and a San Saba Member 310 70- 380 gravity trough extending from the west Point Peak Member 30 380- 410 Morgan Creek Limestone toward the Stribling well. Generally in Member 135 410- 545 the Llano region, large gravity minima WeJge Sand1tone Member 10 545- 555 are associated with Town Mountain Riley Formation 785 555-1,340 Granite (Romberg and Barnes, 1944; Lion Mountain Sandstone Member 35 555- 590 Barnes, Romberg, and Anderson, 1954a, Cap Mountain Limestone 1954b, 1955). The shape of the gravity Member 510 590-1,100 minimum and trough and the presence Hickory Sandstone Member 240 1,100-1,340 of Town Mountain Granite in the Strib­ Precambrian FIG. 1. Gravity and magnetic data, Town Mountain Granite 15 1,340- 1,355 ling well indicate that the Paleozoic Johnson City quadrangle, Texas. Solid rocks in the western and northern halves lines-gravitational force in milligals (relative); dashed lines-magnetic force From the other well, the Winans and of the quadrangle may be underlain by in gammas (relative); dots-points of Forbes No. 1 Buckner 1 mile south of Town Mountain Granite of the Grape gravity observation. 8 Bureau of Economic Geology, The University of Texas

MINERAL RESOURCES

The mineral resources of the quad­ City quadrangle as in the Texas Con­ in 13 analyses. Such small amounts of rangle are limited to nonmetallic con­ struction Material Company quarries lead and zinc indicate that the deposit, struction materials and water except for south of Burnet (Barnes, 1958, pp. 24- at least where sampled near the surface, a minor occurrence of lead and zinc 25) which, in addition to crushed stone, is not of economic importance. Possibly about the exhumed granite dome along produces chemical dolomite. The San there are larger deposits controlled by Pedernales River. Most of the soils (ex­ 'Saba and Threadgill Members along the contact between Cap Mountain Lime­ cept those developed on the Hensell and Pedernales River contain rock of similar stone and the Hickory Sandstone where on alluvium) are not suited to agricul­ grade, as shown by analyses (Cloud the contact intersects the granite at a ture. The greater part of the quadrangle and Barnes, 1948, pp. 377-378, anal. depth of about 400 to 500 feet or more. is ranch land. 12- 28). Most of the Paleozoic dolomite Similar stratigraphic relations appear to in the quadrangle can be used for pro­ have controlled the formation of ore duction of surfacing granules. Some at­ bodies in the southeast Missouri lead CONSTRUCTION MATERIALS tractively colored stone is suitable for district, where buried hills intersect the Dimension slone.-Granite has been terrazzo chip production. contact between the Cambrian Bon­ described by Barnes, Dawson, and Par­ Sand and gravel.-The small deposits neterre Dolomite and the underlying kinson (1947, pp. 25, 48--53) from the of alluvium along Pedernales River, Lamotte Sandstone. North Grape Creek [Rocky Creek] quad­ composed of poorly sorted material up rangle (Barnes, 1952b; MS.). Similar to the size of large boulders, are of little WATER granite is present in the Johnson City value for the production of sand and quadrangle. The granite of the exhumed gravel. The deposits along Towhead and A ground-water survey of Blanco granite hill along Pedernales River takes Flat creeks, composed of material rang­ County (Barnes and Cumley, 1942) in­ an excellent polish and has an unusually ing in hardness from friable limestone ventoried, within the quadrangle, 36 wa­ attractive color, making it a desirable to chert derived from Cretaceous rocks, ter wells, 2 oil tests, and 6 springs. Of monumental and ornamental stone. are unsuited for the production of sand the 21 or so wells situated in Hensell and Other building stone localities de­ and gravel. Glen Rose outcrop areas, most appear to scribed include sandstone and limestone Road material.-On the Johnson City have bottomed in Paleozoic rocks includ­ (Barnes, Dawson, and Parkinson, 1947, topographic quadrangle map, 16 road ing Cap Mountain Limestone, dolomitic pp. 123-124, 130-133). The one deposit material pits are labeled "borrow pits" San Saba, Tanyard Formation, and Gor­ of sandstone sampled is situated 1 mile and 2 are labeled "gravel pits"; the man Formation. Three wells situated on east of Sandy between localities 6-9A reason for the distinction is unknown. Glen Rose Limestone produce water and 6-lOA. The sandstone is mottled Two pits, one near where U. S. Highway probably from the Hensell 'Sand. Seven dark red on a dull pale-red background. 281 leaves the quadrangle to the north wells in the area of Hickory outcrop and It is composed mostly of quartz; micro­ and the other near where it leaves it to 5 situated on Cap Mountain Limestone cline, plagioclase, and glaucon ite are the south, are almost 1,000 feet long. produce from the Hickory Sandstone. common; and a small amount of calcite, A few of the smaller pits, present at Of the 6 springs inventoried, one each is muscovite, and limonite is present. the time the quadrangle was mapped in the Hickory Sandstone, Cap Moun­ One limestone deposit, used in the past geologically, are in calichified conglom­ tain Limestone, Morgan Creek Lime­ and of value only for local building, is erate at the base of the Hensell, in marly stone, San Saba Member, Staendebach 1 mile due east of Sandy at locality material in the Glen Rose, and in calichi­ Member, and Glen Rose Limestone. 6-lOA. The limestone is brownish gray fied colluvium. It is likely that the newer The water wells range in depth from with a slight greenish cast, contains pits are in similar material. Most of the 21 to 298 feet and the depths of the two bright green glauconite, and is in beds material produced has been used for oil tests are 1,210 and 1,585 feet. At the about 6 inches thick. This deposit is near base course material in highway con­ time of the inventory (1942), the wa­ the base of the Cap Mountain Limestone. struction and for surfacing secondary ter surface ranged from 2 to 106 feet Another deposit of Cap Mountain roads. below the surface. Total solids ranged Limestone was examined along the road from 280 to 1,162 parts per million, ex­ to Sandy, where it crosses Buffalo Creek, LEAD AND ZINC cept for one well high in nitrate which and here beds between 6 and 10 inches contained 2,175 parts per million. thick are common. Similar stone is Barnes ( 1956, pp. 28-30) described The Hensel! 'Sand in the southern part widely distributed in the broad belt of the occurrence of lead and zinc in the of the quadrangle contains water, at least Cap Mountain Limestone extending to vicinity of the exhumed granite dome locally, and in the northeastern part of the southwest as well as in the parallel along Pedernales River. The lead occurs the quadrangle Hensell-filled erosion belt of Morgan Creek Limestone. as galena (lead sulfide) and is readily channels in Paleozoic rocks are probably Crushed stone.-Crushed stone of good visible in Cap Mountain Limestone near water-bearing. quality can be produced from all the its contact with the granite. Zinc, pos­ Southeastward-dipping Hickory Sand­ Ordovician and some of the Cambrian sibly as sphalerite (zinc sulfide) is also stone in the northwestern part of the units within the quadrangle, and there present. Lead ranges from 0.01 to 1.47 quadrangle is a good aquifer. In the sub­ are suitable deposits near all dam sites. (aver. 0.31) percent and zinc ranges surface to the east, it produces artesian The same units crop out in the Johnson from 0.00 to 0.21 (aver. 0.14) percent flow in the Stribling ranch well situated Geology of the Johnson City Quadrangle, Blanco County, Texas 9 about 1 mile north-northwest of the Texas, Bur. Econ. Geol. Geologic Blanco and Gillespie counties, Texas: Stratoray Oil Corporation No. 1 Stribling Quad. Map No. 5. Guidebook, San Angelo Geol. Soc. well in which Hickory waler rose to near (1952b) Geology of the Field Conference, March 19-20, 1954, North Grape Creek quadrangle, Gil­ pp. 78-90. the surface. In the western part of John­ lespie and Blanco counties, Texas: ----, , and---- son City, west of the fault along which Univ. Texas, Bur. Econ. Geol. Geo­ (1955) Map showing correlation of Gorman rocks to the east are dropped logic Quad. Map No. 10. geologic, gravity, and magnetic obser­ against Staendebach rocks to the west, ---- (1956) Lead deposits in the vations, Blanco and Gillespie counties, the water-bearing part of the Hickory Upper Cambrian of central Texas: Texas: Univ. Texas, Bur. Econ. Geol. is probably at a depth of 2,000 feet, pro­ Univ. Texas, Bur. Econ. Geol. Rept. BELL, W. C., and ELLINWOOD, H. L. Inv. No. 26, 68 pp. (1962) Upper Franconian and Lower viding the Hickory has not lapped out ---- (1958) Field excursion, east­ Trempealeauan Cambrian trilobites against a buried hill of Precambrian ern Llano region: Univ. Texas, Bur. and brachiopods, Wilberns Formation, rock. Econ. Geol. Guidebook No. 1, 36 pp. central Texas: Jour. Paleont., vol. 36, Lion Mountain Sandstone and Welge (1959) General discussion, pp. 385-423. Reprinted as Univ. Texas, Bur. Econ. Geol. Rept. Inv. No. 47. Sandstone, present in the subsurface in in Stratigraphy of the pre-Simpson Paleozoic subsurface rocks of Texas CLOUD, P. E., JR., and BARNES, V. E. the southeastern two-thirds of the quad­ and southeast New Mexico: Univ. (1948) The Ellenburger Group of cen­ rangle, are about 700 feet nearer to the Texas Pub. 5924, pp. 11-72, Pls. 1-6. tral Texas: Univ. Texas Pub. 4621 surface than the Hickory Sandstone. The ----(MS.) Geology of the Rocky (June 1, 1946), 473 pp. quality of these sandstones as aquifers Creek quadrangle, Gillespie and GEORGE, W. 0. (1947) Geology and is unknown; however, the Welge at least Blanco counties. [Revision of North ground-water resources of Comal probably carries water in places. Grape Creek quadrangle map ('Barnes, County, Texas: Texas State Board of 1952b) .] Water Engineers, 142 pp. Some water is present locally in the ----, and BELL, W. C. (1954) rest of the Paleozoic rocks in fractures, PALMER, A. R. (1954) [1955] The faunas Cambrian rocks of central Texas: of the Riley Formation in central solution channels, and perhaps in some Guidebook, San Angelo Geol. Soc. Texas: Jour. Paleont., vol. 28, pp. 709- of the slightly porous coarse-grained Field Conference, March 19-20, 1954, 786. Reprinted as Univ. Texas, Bur. pp. 35-69. dolomite, but finding it will be fortuitous. Econ. Geol. Rept. Inv. No. 24. ----,,and (MS.) The Moore Hollow Group of central Texas. ROMBERG, F. E., and BARNES, V. E. (1944) Correlation of gravity observa­ REFERENCES ----,,DAWSON, R. F. and PARKIN· tions with the geology of the Smooth· SON, G. A. (1947) Building stones of BARNES, B. A. and CUMLEY, J. S. (1942) ingiron granite mass, Llano County, central Texas: Univ. Texas Pub. 4246 Texas: Geophysics, vol. 9, pp. 79-93; Records of wells and springs, drillers' (Dec. 8, 1942), 198 pp. logs, and water analyses in Blanco Geophys. Case Histories, vol. 1, 1948, -----, ROMBERG, F. E., and ANDER· pp. 415-428. County, Texas: Texas State Board of SON, W. A. (1954a) Correlation of Water Engineers, 56 pp. gravity and magnetic observations WHITNEY, M. I. (1952) Some zone BARNES, V. E. (1948) Ouachita facies in with geology of Blanco and Gillespie marker fossils of the Glen Rose For­ central Texas: Univ. Texas, Bur. Econ. counties, Texas: 19th lnternat. Geol. mation of central Texas: Jour. Geol. Rept. Inv. No. 2, 12 pp. Congress, Algiers, Proc., Sec. 9, pp. Paleont., vol. 26, pp. 65-73. (l952a) Geology of the 151-162. WISE, J.C. (MS.) Cambrian stratigraphy Blowout quadrangle, Gillespie, Blanco, ----, , and---- of the Sandy Post-office area, Blanco and Llano counties, Texas: Univ. (1954b) Geology and geophysics of County, Texas.