Printed on recycled paper

Geologic Framework, Structure, and Hydrogeologic Characteristics of the 

Knippa Gap area in Eastern Uvalde and Western Medina Counties, Texas

By

A.K. Clark, D.E. Pedraza, and R.R. Morris

2013

Suggested citation: Clark, A.K., Pedraza, D.E., and

Morris, R.R., 2013, Geologic framework, structure,

and hydrogeologic characteristics of the Knippa

Gap area in eastern Uvalde and western Medina

Counties, Texas: U.S. Geological Survey Scientific

Investigations Report 2013–5149, 35 p., 1 pl., 

http://pubs.usgs.gov/sir/2013/5149/.

Base from U.S. Geological Survey digital data, various scales

Universal Transverse Mercator projection, zone 14

North American Datum of 1983

Information regarding water resources in Texas is

available at http://tx.usgs.gov

Prepared in cooperation with the

U.S. Army Corps of Engineers

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5149

Mapped hydrogeologic units and cross sections, 2013—Sheet 1 of 1

Clark, A.K., Pedraza, D.E., and Morris, R.R., 2013, Geologic framework, structure, and hydrogeologic

characteristics of the Knippa Gap area in eastern Uvalde and western Medina Counties, Texas

T E X A S

Study area

UVALDE

COUNTY

MEDINA

COUNTY

Trinity 

aquifer

San Antonio 

segment of the 

Edwards aquifer BALCONES FAULT 

ZONE

BEXAR

COUNTY

0 2.5 5 7.5 10 KILOMETERS

0 2.5 5 7.5 10 MILES

EXPLANATION

SystemTertiary

Upper confining unit 

to Edwards aquifer

Edwards

aquifer

None

Upper Cretaceous Lower 

Cretaceous

Maverick Basin

Group or Formation

Devils River

Group or Formation

Hydrologic 

Unit

Ki Ki

Escondido Formation

Anacacho Limestone

Austin Group

Eagle Ford Group

Buda Limestone

Del Rio Clay

Devils River Formation

Escondido Formation

Anacacho Limestone

Austin Group

Eagle Ford Group

Buda Limestone

Del Rio Clay

Salmon Peak Formation

Kes

Kan

Kau

Kef

Kbu

Kdr

Kdrv

Tei

Kes

Kan

Kau

Kef

Kbu

Kdr

Ksa

Study boundary

Contact—Dashed where inferred

Fault—Dashed where inferred

Fracture

Facies change

City boundary

Line of section

Inferred structural dip

Well and well identifier 

 (appendix 1)

Indio Formation

IgneousIgneous

A A'

YP–69–43–106

Structural trough of the

Knippa Gap area

Approximate width of

 the structural trough

YP–69–36–800

YP–69–36–9xx

YP–69–51–602

YP–69–52–403

YP–69-50-309 YP–69–44–704a

YP–69–44–806a

YP–69–45–8xx

YP–69–43–804

YP–69–45–701a

YP–69–43–605

YP–69–43–606

YP–69–43–403

YP–69–43–409

YP–69–43–103

YP–69–43–106 YP–69–43–202 YP–69–43–301b

TD–69–38–905a

YP–69–36–602

YP–69–37–402

YP–69–51–606

YP–69-42-902

YP–69–44–902

YP–69–44–808a

YP–69-42-911

YP–69–46–102

YP–69–36–904

YP–69–52–7xx

YP–69–52–9xx

YP–69–51–408

YP–69–51–6xxb

YP–69–51–1xxc

YP–69–52–201

YP–69–51–301a

YP–69–51–1xxa

YP–69–53–2xx

YP–69–51–104

TD–69–45–101

TD–69–45–105

TD–69–45–108

TD–69–45–102 TD–69–45–109

TD–69–45–103

TD–69–45–104

TD–69–45–203

TD–69–45–201

TD–69–45–202

TD–69–45–301

TD–69–45–303

TD–69–45–302

YP–69–45–405

YP–69–45–406

YP–69–45–402

YP–69–45–501

YP–69–45–504

YP–69–45–4xx

YP–69–45–802

YP–69–45–704

YP–69–45–701b

YP–69–45–702

YP–69–45–703

YP–69–45–7xx

YP–69–44–9xx

YP–69–44–806b YP–69–44–807

YP–69–44–808b

YP–69–44–703

YP–69–44–704b

YP–69–44–502 YP–69–44–601 YP–69–44–503

YP–69–44–5xx

YP–69–44–4xxa

YP–69–44–4xxb

YP–69–44–402

YP–69–44–401 YP–69–44–404

YP–69–44–406

YP–69–44–405

YP–69–44–407

YP–69–44–305

YP–69–44–303

YP–69–44–301

YP–69–44–302

YP–69–44–304

YP–69–44–203

YP–69–44–201

YP–69–44–204

YP–69–44–109

YP–69–44–110

YP–69–44–106

YP–69–44–102

YP–69–44–101

YP–69–44–103

YP–69–44–105

YP–69–43–307

YP–69–43–308

YP–69–43–302

YP–69–43–303

YP–69–43–306

YP–69–43–305

YP–69–43–301a

YP–69–43–205

YP–69–43–3xxc

YP–69–43–105

YP–69–43–108

YP–69–43–109

YP–69–43–4xxa

YP–69–43–4xxb

YP–69–43–4xxc

YP–69–43–4xxd

YP–69–43–4xxe YP–69–43–4xxf

YP–69–43–408

YP–69–43–410

YP–69–43–402

YP–69-42-606

YP–69–43–502

YP–69–43–503

YP–69–43–601

YP–69–43–603

YP–69–43–6xx

YP–69-42-9xx

YP–69–43–7xxa

YP–69–43–7xxb

YP–69–43–7xxc

YP–69–43–7xxd

YP–69–43–803

YP–69–43–802

YP–69–43–916

YP–69–43–902

YP–69–43–912

YP–69–43–905

YP–69–43–908

YP–69–43–909

YP–69–43–917

TD–69–46–101

TD–69–46–102

TD–69–46–1xx

TD–69–46–6xx

TD–69–38–905b

TD–69–46–404

TD–69–46–405

TD–69–38–1xxb

TD–69–46–8xxb

TD–69–38–101

TD–69–38–103

TD–68–31–1xxa

TD–68–31–1xxb

TD–68–31–1xxc

TD–69–46–8xxa

TD–69–38–1xxa

YP–69–43–9xx

YP–69–44–8xx

YP–69–45–5xx

YP–69–45–400

YP–69–43–3xxa

YP–69–51–102

YP–69–51–1xxb

YP–69–51–205

YP–69–51–204

YP–69–51–203

YP–69–51–301b

YP–69–51–2xxa

YP–69–51–2xxb

YP–69–51–2xxc

YP–69–51–2xxd

YP–69–51–2xxe

YP–69–51–5xx

YP–69–51–6xxa

YP–69–51–6xxc

YP–69–44–408

YP–69–43–2xx

Ki

Tei

Ki

Ki

Kau

Kef

Kau

Kbu

Kef

Kdr

Kbu

Kdr

Kdr Kbu

Ksa

Kef

Kdr Kdr Kau

Ki Ki Kau Kdr

Kef Ksa Kef

Ki

Kbu

Kau

Kef Kdr Kdr Kbu

Ki

Kbu

Kau Ki

Kbu

Ki Kbu

Ksa Kbu

Kdr Kan

Kau

Ki Kef

Ki

Kan

Kef

Ki

Kbu

Kau

Kdr

Kan

Ksa

Kau

Ki

Kef

Kbu

Kbu

Kef Kbu

Ki

Ki

Kan

Kbu Ksa

Kef

Kbu Kbu Ki

Ki

Kdr

Kbu

Kau

Ksa

Ki

Kdr

Kef

Ki

Kef

Kbu

Kau

KefKau

Kef

Kbu

Kef

Kdr

Kdr

Kdr

Kbu Kan Kbu

Kbu Kdr

Kdr

Kdr Kbu

Kes

Kef

Kdr

Kbu

Kdrv

Kan

Ksa Kdr

Kau

Kes

Kau Kef Kan

Kau

Kdrv

Kan

Kau

Kau

Kbu

Kef

Kan

Kau

Kan

Kdrv

Kan

Kan

Kau

Kef

Kbu

Kau

Kau

Kau

Kan Kan Kau Kau

Kau

Kbu Kef

Kef

Kau Kef

Kbu Kbu

Kau

Kbu Kbu

Kau

Ki Kdr

Kau

Kau

Kbu

Kbu

Kef

Kdr

Kdr

Kdr

Kau

Kbu

Kbu

Kef

Kbu

Kef

Kdrv

Kdr

Kbu Kbu Kbu Kef

Kau

Kdr Kbu

Kdrv

Kbu

Kau

Kdrv

Kdr Kbu Kef

Kdrv

Kdrv

Kdr

Kbu

Kan

A

A'

B'

B

UVALDE

COUNTY

MEDINA 

COUNTY

Uvalde

Sabinal

Knippa

99°16'15"

99°24'

99°31'45"

99°39'30"

99°47'15"

29°28'45"

29°21'

29°13'15"

99°16'15"

99°24'

99°31'45"

99°39'30"

99°47'15"

29°28'45"

29°21'

29°13'15"

Ki

Ki

Ki

Kef

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Ki

Kbu

Ki

Ksa

Ksa

Kbu

Ki

Ki

Ki

Ki

Kan

Kan

Kan

Kan

Kan

Kbu

Kbu

GULF OF MEXICO

Base modified from U.S. Geological Survey 1:24,000-scale digital data

Universal Transverse Mercator projection, zone 14

North American Datum of 1983

Kdr

Qle

Qle

Qle

Qle

T-Qu

T-Qu

T-Qu

T-Qu

T-Qu

T-Qu

T-Qu

Sabinal

Uvalde

Knippa

29°28'45"

29°21'

29°13'15"

99°47'15" 99°39'30" 99°31'45" 99°24' 99°16'15"

0 2.5 5 7.5 10 MILES

0 2.5 5 7.5 10 KILOMETERS UVALDE COUNTY MEDINA COUNTY

A

A'

B'

B

A A'

Study boundary

Line of section

Fault—Dashed where inferred

Fracture

Relay ramp—Inferred

Uvalde Salient—Inferred

System Epoch Quaternary

Leona 

aquifer None

Quaternary

or Tertiary

Pliocene Pleistocene

Formation Hydrologic Unit

Qle Leona Formation

T-Qu Uvalde Gravel

EXPLANATION

Uvalde Salient

Relay ramp

Structural trough of the

Knippa gap area

Approximate width of 

the structural trough

T-Qu

Base modified from U.S. Geological Survey 1:24,000-scale digital data

Universal Transverse Mercator projection, zone 14

North American Datum of 1983

Frio River

Nueces River

Seco Creek

Creek

Sabinal River

River

Medina

Lake

Medina

Hondo

KINNEY COUNTY

UVALDE COUNTY

MEDINA COUNTY

Brackettville

Knippa

Uvalde

Sabinal

Hondo

Western storage unit

Western Medina

storage unit Eastern Medina 

storage unit

100°00' 99°30' 99°00' 100°30'

29°30'

29°15'

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

EXPLANATION

San Antonio segment of the

 Edwards aquifer recharge

 zone in Kinney, Medina, and

 Uvalde Counties, Texas (George

 and others, 2011)

 Edwards aquifer outcrop

 Edwards aquifer subcrop

Approximate downdip limit of the 

 freshwater zone in the Edwards

 aquifer (A.L. Schultz, written

 commun., 2000)

Study area boundary

Rio Grande

Base modified from U.S. Geological Survey 1:250,000-scale digital data

Universal Transverse Mercator projection, zone 14

North American Datum of 1983

Frio River

Leona River

C. Storage units and unconfined and confined zones of the Edwards aquifer in Kinney, Medina, and Uvalde Counties, Texas.

E. Cross section B–B'

D. Cross section A–A'

B. Location of the Leona Formation and Uvalde gravels in and around the study area.

A. Mapped hydrogeology and faulting BEND IN SECTION BEND IN SECTION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

YP–69–52–201

YP–69–45–701a

YP–69–44–806a

YP–69–44–902

YP–69–51–606

YP–69–52–403

YP–69–45–5xx

YP–69–46–102

YP–69–51–6xxb

TD–69–38–905a

TD–69–38–905b

0 2,000 4,000 6,000 FEET

VERTICAL SCALE GREATLY EXAGGERATED

-850

-800

-750

-700

-650

-600

-550

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

NAVD 88

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1,000

1,050

1,100

1,150

FEET

FB19

FB16 FB16a FB15 FB14 FB20

SOUTHWEST NORTHEAST

FB19a

A A'

Approximate width of the 

structural trough

SECTION

B–B'

NAVD 88, North American Vertical Datum of 1988

Hydrologic unit

 Upper confining unit to

 Edwards aquifer

 Edwards aquifer

 Trinity aquifer

Land surface

Fault—Dashed where

 inferred. Arrow shows

 relative movement

Well

Well identifier (appendix 1)

Fault block identifier

YP–69–43–106

FB01

EXPLANATION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

BEND IN

SECTION

YP–69–53–2xx

YP–69–45–8xx

YP–69–45–400

YP–69–45–5xx

YP–69–36–9xx

YP–69–36–904

YP–69–36–602

-1,100

-1,050

-1,000

-950

-900

-850

-800

-750

-700

-650

-600

-550

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1,000

1,050

1,100

1,150

1,200

FEET

NAVD 88

FB02

FB03 FB04 FB05 FB07 FB08 FB09 FB11 FB12 FB14 FB15 FB16 FB17 FB18

FB01

FB10 FB13 FB06

NORTHWEST SOUTHEAST

0 2,000 4,000 6,000 FEET

VERTICAL SCALE GREATLY EXAGGERATED

B B' SECTION

A–A'

NAVD 88, North American Vertical Datum of 1988