Kkke

Kkg

Kplc

Kprd

Kkd

Kpcm

Kplc

Kpcm

Kpcm

Kg

Kg

Kplc

Kplc

Kdr

Kkd

Kkd

Kplc

Kprd

Kkg

Kkg

Kkke

Kkke

Kkke

Kpcm

Kplc

Kkd

Kprd Kprd Kkd

Kkg

Kkd

Kkke

Kkke

Kkke

Kkg

Kkbn

Kkbn

Kprd Kkd

Kgrcb

Kwc

Kkd

Kkg

Kkke

Kkke

Kkd

Kgrcb

Kgrcb

Kgrcb

Kgrf

Kgrue

Kgrcb

Kkke

Kkke

Kkke

Kkke

Kplc

Kkg

Kkg

Kkd

Kkd

Kkd

Kkd

Kgrf

Kkd

Kgrcb

Kkd

Kkd

Kkd

Kkd

Kkd

Kgrcb

Kgrue

Kgrf

Kkke

Kkke

Kkd

Kkd

Kplc

Kplc

Kprd

Kgrcb

Kgrcb

Kkd

Kkd

Kkke

Kkke

Kkg

Kkd

Kkd

Kgrcb

Kgrcb

Kgrue

Kgrcb

Kgrb

Kgrlb

Kgrts

Kgrb

Kgrr

Kgrhc

Kgrd

Kgrle

Kgrf

Kgrts

Kgrhc

Kgrb

Kgrb

Kgrcb

Kgrb

Kgrcb

Kgrf

Kgrf

Kgrcb

Kgrf Kgrf

Kgrf

Kgrue

Kgrue

Kgrue

Kgrue

Kgrcb

Kwc

Kkd

Kkd

Kgrf

Kkke

U

D

U D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U D

U

D

U D

U D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U D

U

D

U

D

U D

U

U D

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

U

D

Kgrue

Kwc

Kwc

Kwc

Kwc

Kkke

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kwc

Kgrle

Kgrle

Kkg

Kgrle

Kwc

Kdr

Kgrue

Kgrue

MAP EXPLANATION

Fault—Type unspecified, dashed where inferred; U, upthrown block; 

D, downthrown block

Contact—Between hydrostratigraphic units

Corbula bed contact—The Corbula sp. bed

Study boundary

Strike and dip of hydrostratigraphic unit

Cave—Orientation unspecified

Sink

Spring

U

D

50

§ ̈¦35

§ ̈¦35

§ ̈¦35

§ ̈¦410

§ ̈¦37

£¤281

£¤290

£¤281

£¤281

UV46

§ ̈¦10

§ ̈¦10

UV16

UV173

§ ̈¦10

£¤290

1604

Blanco River

River

Little Blanco

Medina

Guadalupe

River

River

Medina

San Antonio

River

River

Honey

Creek

San Antonio

San

Marcos

Bandera

Round

Mountian

Wimberley

Saint 

Hedwig

Kyle

Bulverde

Somerset

Blanco

New

Braunfels

Johnson

City

Buda

Boerne

Dripping Springs

Twin 

Sisters

Pipe Creek

Medina

Lake

Canyon

Lake

KENDALL

COUNTY

HAYS

COUNTY

COMAL

COUNTY

BLANCO

COUNTY

BANDERA

COUNTY

BEXAR

COUNTY

BALCONES FAULT ZONE

97°52'30"

98°15'00"

98°37'30"

99°00'00"

99°22'30"

30°22'30"

30°00'00"

29°37'30"

29°15'00"

0 5 10 15 20

0 5 10 15 20 KILOMETERS

MILES

EXPLANATION

Edwards aquifer

Trinity aquifer

USGS 7.5-minute quadrangle 

 study area boundary

Balcones fault zone

Base modified from U.S. Geological Survey digital 

data at 1:100,000-scale

Universal Transverse Mercator, zone 14

North American Datum of 1983

Comal Springs

Government Canyon

State Natural

Area

Camp 

Bullis

Camp 

Stanley

Magic Springs

Figure 1. Location of the study area, Driftwood and Wimberley 7.5-minute quadrangles, Hays and Comal Counties, Texas. Aquifers from George and others, 2011.

Ouachita Structural Belt

TEXAS

BALCONES FAULT ZONE

Trinity aquifer

Edwards aquifer

COMANCHE SHELF

San Marcos

Platform

Study area

Wimberley 

Quadrangle

Ancestral Gulf Of Mexico

Present–day

Gulf Of Mexico

Stuart City Reef

Trend

Wimberley 

Quadrangle

Driftwood Quadrangle

98 ̊07’30” 30 ̊07’30” 98 ̊00’

30 ̊07’30” 2’30” 5

85000 m E 586 587 588 589 590 591 592 593 594 595 596

3332

3331

30 30 ̊00’  ̊00’

3318

3317

3316

3315

57’30”

29 ̊52’30”

98 ̊00’

29 ̊52’30”

2’30” 5

85 5

86 587 588 589 590 591 592 5

93 594000 m E 595 596 98 ̊07’30”

3306000 m N

3329

3330

3328

5 ́

3327

3326

3325

3324

2 ́30”

3323

3322

3321

3320000 m N

3314

3313

3312

3309

55’

3311

3310

3308

3307

3308

3307

3306

3316

3315

3314

57’30”

3313

3312

3311

3310

3309

55’

3318000 m N

3317

3320

3321

3322

2 ́30”

3324

3325

3326

3327

3328

5’

3329

3330

3331

3332000 m N

Orbitolina texana

(Roemer, 1852), 

limestone beds thicker 

and more resistive 

than overlying and 

underlying patch reefs 

formed on rudist, reefal 

talus 

Thick argillaceous beds, 

thin shale beds, Orbitolina 

texana (Roemer, 1852), 

contains ponds and 

seeps, often little 

vegetation, steeper slopes 

often with “badlands” type 

weathering, thinner in areas 

where patch reefs are 

present in the underlying 

Doeppenschmidt HSU

Forms stair-step 

topography with soils,

Orbitolina texana

(Roemer, 1852)

BU, VUG, 

FR, BP,

BR, CV

FR, CV

IP, BU, 

FR, BP,

CV

IP, MO,

VUG, FR,

BR, CV 

IP, MO,

BU, BP, 

FR, CV 

BU, BP, 

FR, 

occasional

CV

IP, MO, 

BU, BR 

MO, BR, 

BP, FR

MO, BU, 

BP, FR

IP

IP, MO,

BU, BP, 

FR, CV 

IP, FR, CV

IP, MO, 

BU, BP, 

FR, CH, 

CV

MO, BU,

FR, CV 

IP, IC,

MO, BU,

VUG, FR,

BP, CV

Aquifer

Confining

Aquifer

Aquifer

Aquifer

Aquifer,

confining unit in 

areas without 

caves 

Confining

Semi-confining

Aquifer

Semi-confining

Aquifer

Semi-confining;

Confining 

shale beds

Aquifer

Semi-confining

Aquifer

Confining

Confining

Aquifer

70–90

20

40

40–50

90–120

40

10

30–40

(typically 30)

30–40

(typically 30)

30–40

(typically 30)

40–80

(typically 40)

40–70

(typically 40)

45–60

(typically 55)

120–130

230

III

IV

V

VI

VII

VIII

Camp Bullis 

Fossiliferous 

Lower

evaporite 

Little Blanco 

Twin Sisters

Doeppenschmidt

Rust

Honey Creek 

Bulverde

II

Middle zone of the Trinity aquifer Upper zone of the Trinity aquifer

Edwards aquifer

Trinity aquifer

Wackestone, packstone, grainstone, 

boundstone, burrows; caprinid, miliolid, 

Orbitolina texana (Roemer, 1852), 

Toucasia sp., Trigonia sp., Turritella sp., 

various corals, pectens, shell fragments

Alternating beds of argillaceous wackestone, 

packstone; mudstone, wackestone, 

packstone, grainstone, milliolid grainstone; 

monopleurid, Nerinia sp., Orbitolina 

texana (Roemer, 1852), Tylostoma sp., 

and oysters, pectens, and pelecypods 

Mudstone, wackestone, packstone, 

grainstone, boundstone, argillaceous 

wackestone and packstone, miliolid 

grainstone; caprinid, Toucasia sp.

Argillaceous wackestone, shale; Orbitolina

texana (Roemer, 1852), gastropods, 

pelecypods

Mudstone, wackestone, argillaceous 

wackestone, boundstone; caprinid, 

monopleurid, Toucasia sp., 

Orbitolina texana (Roemer, 1852), 

gastropods, pectens, pelecypods

Wackestone, grainstone, argillaceous 

wackestone, shale, evaporites;

monopleurid, Toucasia sp., 

Macraster sp., Nerinia sp., Orbitolina 

texana (Roemer, 1852), Porocystis 

golobularis, Salenia texana, gastropods, 

pecten, and pelecypods

Dissolved evaporites, highly altered 

crystalline limestone and chalky mudstone, 

breccia, boxwork voids; Corbula beds

Alternating wackestone, packstone,

miliolid grainstone, argillaceous limestone,

mudstone, silty mudstone at base; 

Hemiaster sp., Neithea sp., Orbitolina minuta

(Douglas, 1960), Porocystis golobularis, 

Protocardia texana, Tapes decepta, 

Turritella sp., gastropods, mollusks;

(section not subdivided into an upper and 

lower unit as in Bexar and Comal Counties)

Alternating beds of burrowed wackestone, 

packstone, miliolid grainstone, argillaceous

limestone

Shaley, nodular limestone, burrowed 

mudstone, wackestone, packstone, miliolid 

grainstone, dolomite, contains dark, spherical

textural features locally known as black 

rotund bodies (BRBs); caprinid, Ceratostreon

[Exogyra] texana, miliolid, gastropods; area 

transitions to basal nodular containing oyster 

beds and shale 

Chert (absent in lower 20 ft), dolomitic 

mudstone, wackestone, packstone, 

grainstone 

Highly altered crystalline limestone, chalky

mudstone, occasional grainstone associated

with tidal channels; chert (beds and nodules);

coarse-grained spar, breccia and travertine,

dissolution has removed all evaporites in 

the study area

Miliolid, skeletal fragmented grainstone,

mudstone, wackestone; chert (beds and 

nodules); cross-bedded and ripple marked 

Dense, shaley, mudstone, wackestone, 

oyster-shell mudstone and wackestone,

iron staining, chert 

Recrystallized limestone, mudstone, 

wackestone, packstone, grainstone; chert 

(bedded and large nodules); iron-stained, 

stromatolitic, Toucasia sp., Montastrea 

roemeriana, oysters

Cyclic and

marine

 (undivided) 

Leached and

collapsed

(undivided) 

Regional dense Grainstone Kirschberg evaporite 

Dolomitc *

Early Cretaceous

Lower

Cretaceous

Trinity

Upper

Glen Rose Limestone Kainer

Edwards

Person Georgetown

Late Cretaceous

Washita

80–90

20–30

*

Fossiliferous blue-green to yellow-brown

clay, packstone, iron nodules; Ilymatogyra 

arietina 

*

Confining 

unit

Period

Epoch

Group

Formation

Member

(formal and informal)

Lithology and ichnology

Hydrologic unit

Hydrostratigraphic unit1

(HSU)

Thickness2

(outcrop in the 

study area,

 in feet) 

Hydrologic

function 

Porosity

type Field identification

Map abbreviations

and color

Geology Hydrostratigraphy

Table 1. Summary of bedrock geology and hydrostratigraphy of the Edwards and Trinity aquifers within the Driftwood and Wimberley 7.5-minute quadrangles, Hays and Comal Counties, Tex. 

1

Informal

2

Thickness range based on field mapping in the study area

Thick beds of 

wackestone, packstone,

grainstone; corals, 

caprinid, Trigonia sp., 

cliff forming; outcrop 

often contains large 

limestone float with large 

channel and moldic

porosity, caves and 

springs 

Limestone beds thicker

and more resistive to 

erosion than overlying and 

underlying units, Orbitolina

texana (Roemer, 1852), 

patch reefs

Salinia texana bed 

immediately below 

Corbula bed, abundant 

fossils including 

Porocystis golobularis,

Orbitolina texana 

(Roemer, 1852), 

Macraster sp., Nerinia sp., 

pecten, gastropods, 

pelecypods

Weathers to an orangish 

red with a pebbly texture, 

often has less cedar 

growth and thicker grasses,

boxwork porosity, 

Corbula sp., spring and 

seeps

Limestone and 

argillaceous limestone,

Orbitolina minuta 

(Douglas, 1960)

Alternating beds of

limestone and argillaceous

limestone, fossils rare, 

stair-step topography

Massive, nodular and 

mottled limestone, BRBs 

and orange wisps, 

Ceratostreon 

[Exogyra] texana, seeps 

and springs, ferns 

growing near contact of 

underlying unit

Massively bedded light 

gray, Toucasia sp., 

abundant

Boxwork porosity with 

neospar and travertine 

frame

Cross-bedded, ripple 

marks, miliolid 

grainstone

Wispy iron-oxide stains,

thin bedded, often white 

in aerial photographs

Bioturbated iron-stained

beds separated by 

massive limestone beds; 

stromatolitic limestone,

Montastrea roemeriana

I

Del Rio 

Clay 

Black dendrites, iron

nodules and staining,

Plesioturrilites brazoensis,

Waconella wacoensis

Thin graded cycles; 

massive beds to relatively 

thin beds; cross-beds, 

caprinids

Clay, holds water,

fossiliferous; Ilymatogyra

arietina

Reddish-brown, gray to light tan shaley

mudstone and wackestone, black dendrites,

iron nodules, iron staining; Plesioturrilites 

brazoensis, Waconella wacoensis 

Kplc

Kprd

Kkg

Kkke

Kkd

Kkbn

Kgrle

Kgrf

Kgrcb

Kgrb

Kgrlb

Kgrts

Kgrd

Kgrr

Kgrhc

Kdr

Kpcm

Kg

Pelletal limestone, mudstone, miliolid

grainstone, packstone, chert (bedded and 

large nodules); caprinid, cross-bedded 

MO

MO, BU,

VUG, BP,

FR, CV

40–50 None

[Period, Epoch, Group, Formation, members, and lithology modified from Imlay (1945), Whitney (1952), Lozo and Stricklin (1956), Stricklin and others (1971), Rose (1972), Stricklin and Smith (1973), Amsbury (1974), Inden 

(1974), Perkins (1974), Clark and others (2009, 2013, 2014), Weirman and others (2010), Blome and Clark (2014), and the U.S. Geological Survey National Geologic Map Database, GEOLEX 

(http://ngmdb.usgs.gov/Geoloex.html); Orbitolina minuta (Douglas, 1960), Orbitolina texana (Roemer, 1852); aquifers from Maclay and Small (1976), and Ashworth (1983); thickness from outcrop, Clark and others (2009, 

2014), Weirman and others (2010); hydrologic function modified from outcrop (Clark and others, 2009, 2013, 2014; Weirman and others, 2010; Clark and Morris, 2015); porosity types modified from Choquette and Pray 

(1970). 

Fabric selective: IP, Interparticle porosity; IC, Intercrystalline porosity; SH, Shelter porosity; MO, Moldic porosity; BU, Burrowed porosity; FE, Fenestral; BP, Bedding plane porosity.

Not-fabric selective: FR, Fracture porosity; CH, Channel porosity; BR, Breccia; VUG, vug porosity; CV, Cave porosity; *no further subdivision; **not present in the study area]

Basal

nodular

Kwc

Walnut Clay

*

Kgrue

Dissolved evaporites, highly altered

crystalline limestone and chalky mudstone,

breccia, boxwork voids

IP, MO,

BU, BR Aquifer Upper 10evaporite Spring and seeps

* *

*

Kgrue Upper evaporite 

I

Del Rio Clay Kdr

Upper Glen Rose

Limestone

Upper Confining

Unit (UCU)

Lower Glen Rose

Limestone

Glen Rose

Limestone

Kainer

Person

Georgetown

Grainstone

Kirschberg evaporite

Dolomitic

Member 

Formation (Formal and informal)

Informal 

hydrostratigraphic 

unit

EXPLANATION OF HYDROSTRATIGRAPHIC UNITS

II

III

IV

V

VI

VII

VIII

Camp Bullis

Fossiliferous

Lower evaporite

Bulverde

Little Blanco

Twin Sisters

Doeppenschmidt

Rust

Honey Creek

Kg

Kpcm

Kplc

Kprd

Kkg

Kkke

Kkd

Kgrcb

Kgrf

Kgrle

Kgrb

Kgrlb

Kgrts

Kgrd

Kgrr

Kgrhc

Basal nodular

Cyclic and marine, undivided

Leached and collapsed, undivided

Regional dense member

Kwc

Walnut Kkbn

Clay

4°

50

49

9072

50

60

6

33

75

7

11

90

12

90

TOM

FAULT

TOM 

CREEK

FAULT

CREEK

WIMBERLEY

FAULT

WIMBERLEY

FAULT

HIDDEN

FAULT

VALLEY

Stephen’s sink

SCALE 1: 24 000

CONTOUR INTERVAL 20 FEET

NORTH AMERICAN VERTICAL DATUM OF 1988

1 1/ 2 0 1 MILE

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

Scientific Investigations Map 3386

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey

Bedrock Geology and Hydrostratigraphy of the Edwards and Trinity Aquifers Within the 

Driftwood and Wimberley 7.5-Minute Quadrangles, Hays and Comal Counties, Texas

By

Allan K. Clark and Robert R. Morris

2017

APPROXIMATE MEAN

DECLINATION, 2016 TRUE NORTH

MAGNETIC NORTH

TEXAS

LOCATION OF QUADRANGLES

For additional information, contact

Director, USGS Texas Water Science Center

U.S. Geological Survey

1505 Ferguson Lane

Austin, Texas 78754-4501

Or visit the Texas Water Science Center Web site at 

http://tx.usgs.gov/

ScienceBase citation: Clark, A.K., Pedraza, D.E., and Morris, R.R., 2017, Data release of the bedrock geology and hydrostratigraphy of the Edwards and Trinity aquifers 

within the Driftwood and Wimberley 7.5-minute quadrangles, Hays and Comal Counties, Texas: U.S. Geological Survey data release, https://doi.org/10.5066/F76D5RXQ.

Suggested citation: Clark, A.K., and Morris, R.R., 2017, Bedrock geology and hydrostratigraphy of the Edwards and Trinity aquifers within the Driftwood and Wimberley 

7.5-minute quadrangles, Hays and Comal Counties, Texas: U.S. Geological Survey Scientific Investigations Map 3386, 12 p., 1 sheet, scale 1:24,000, 

https://doi.org/10.3133/sim3386.

Publishing support provided by 

Denver Publishing Service Center

To learn about the USGS and its information products visit

http://www.usgs.gov/

1-888-ASK-USGS

ISSN 2329-132X (online)

https://doi.org/10.3133/sim3386

For more information concerning this publication, contact 

Director, USGS Texas Water Science Center

U.S. Geological Survey

1505 Ferguson Lane

Austin, Texas 78754–4501

(512) 927-3500

Or visit the Texas Water Science Center Web site at

http://tx.usgs.gov/

Original data were collected in the field with the use of handheld global 

positioning system (GPS) enabled devices. While in the field mapping, 

attributes were tagged to the waypoints.

Lithologic and hydrostratigraphic descriptions are from field observations

and previous investigations.

Digital cartography and geographic information systems (GIS) database

by Diana E. Pedraza

Edit and digital layout by J.A. Herrick

Manuscript approved for publication August 30, 2017

Base from U.S. Geological Survey 7.5-minute quadrangles 

Driftwood 1964, rev. 1986; and Wimberley, Tex. 1989

U.S. Geological Survey bases downloaded from and cropped by 

Texas Natural Resources Information System accessed on 

March 2017 at https://tnris.org/

North American Datum of 1983 (NAD83)

Universal Transverse Mercator Projection, zone 14

Any use of trade, firm, or product names is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also 

may contain copyrighted materials as noted in the text. Permission to reproduce 

copyrighted items must be secured from the copyright owner.

This database, identified as SIM 3386, has been approved for release and 

publication by the U.S. Geological Survey (USGS). Although this database has been 

subjected to rigorous review and is substantially complete, the USGS reserves the 

right to revise the data pursuant to further analysis and review. Furthermore, the 

database is released on condition that neither the USGS nor the U.S. Government 

shall be held liable for any damages resulting from its authorized or unauthorized 

use.

Although these data have been processed successfully on a computer system at the 

U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding 

the display or utility of the data on any other system or for general or scientific 

purposes, nor shall the act of distribution constitute any such warranty. The USGS 

or the U.S. Government shall not be held liable for improper or incorrect use of the 

data described and/or contained herein.

This map or plate is offered as an online-only, digital publication. Users should be 

aware that, because of differences in rendering processes and pixel resolution, 

some slight distortion of scale or color may occur when viewing it on a computer 

screen or when printing it on an electronic plotter, even when it is viewed or printed 

at its intended publication scale.

Index map showing map area in yellow and adjacent 

U.S. Geological Survey (USGS) 7.5-minute 

quadrangles. 

30°07’30”

30°00’00”

98°00’00”

DRIFTWOOD

DEVILS

BACKBONE

WIMBERLEY

HENLY DRIPPING

SPRINGS

ROUGH HOLLOW

98°15’00” 98°07’30”

29°52’30”

30°15’00”

MOUNTAIN

CITY

SIGNAL

HILL

SAN MARCOS

NORTH

SATTLER HUNTER SAN MARCOS

SOUTH

29°45’00”

97°52’30”

CONVERSION FACTORS

2.54 centimeter (cm)

25.4 millimeter (mm)

0.3048 meter (m)

1.609 kilometer (km)

Multiply

Length

By To obtain

inch (in.)

inch (in.)

foot (ft)

mile (mi)