10′ 105° 50′ 40′ 30′ 20′ 104°10′ 41°40′

30′

20′

10′

41°

0.1 to 99

100 to 199

200 to 299

300 to 399

400 to 499

EXPLANATION

Estimated saturated thickness, 

 March–June 2009, in feet

T. 12 N.

T. 13 N.

T. 14 N.

T. 15 N.

T. 16 N.

T. 17 N.

T. 18 N.

T. 19 N.

R. 70 W. R. 69 W. R. 68 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R. 61 W. R. 60 W.

Boundary of mapped data

Unsaturated or insufficient data

Area where Ogallala and (or) Arikaree aquifers 

 not present within boundary of mapped data

WYOMING

COLORADO

WYOMING

NEBRASKA

PLATTE COUNTY

LARAMIE COUNTY

GOSHEN COUNTY

ALBANY COUNTY

LARAMIE COUNTY

Base from Beartooth Mapping Inc. Digital Raster Graphics (DRG-E), 1982−84, 1:100,000

Universal Transverse Mercator projection, zone 12

North American Datum of 1927

LAND-SURFACE CONTOUR INTERVAL 10 METERS

NATIONAL GEODETIC VERTICAL DATUM OF 1929

0

0 5 10 15

10

20 KILOMETERS

5 15 20 MILES

10′ 105° 50′ 40′ 30′ 20′ 104°10′ 41°40′

30′

20′

10′

41°

50 to 99

100 to 199

200 to 299

Greater than or equal to 300

EXPLANATION

Estimated depth to water, 

 March–June 2009, in feet

Base from Beartooth Mapping Inc. Digital Raster Graphics (DRG-E), 1982−84, 1:100,000

Universal Transverse Mercator projection, zone 12

North American Datum of 1927

LAND-SURFACE CONTOUR INTERVAL 10 METERS

NATIONAL GEODETIC VERTICAL DATUM OF 1929

T. 12 N.

T. 13 N.

T. 14 N.

T. 15 N.

T. 16 N.

T. 17 N.

T. 18 N.

T. 19 N.

R. 70 W. R. 69 W. R. 68 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R. 61 W. R. 60 W.

Boundary of mapped data

Less than 50

WYOMING

COLORADO

WYOMING

NEBRASKA

PLATTE COUNTY

LARAMIE COUNTY

GOSHEN COUNTY

ALBANY COUNTY

LARAMIE COUNTY

0

0 5 10 15

10

20 KILOMETERS

5 15 20 MILES

Figure 1. Relation of geologic units to hydrogeologic units, High Plains aquifer system, Laramie County, Wyoming.

Era System Series Hydrogeologic unit Lithology Water supply

Miocene

Oligocene2

Cenozoic

Tertiary

Upper Lower

Stream-laid deposits composed of varying amounts 

of gravel, sand, silt, and clay.

Primarily heterogeneous mixture of unconsolidated 

and (or) weakly to firmly cemented gravel, sand, silt, 

and clay.

Primarily massive and cross-stratified, moderately 

cemented, very fine to fine-grained sandstone, with 

beds of siltstone and thin beds of volcanic ash. 

Locally, a coarse conglomerate occurs at base.

Primarily massive, weakly to moderately cemented 

siltstone with claystone. Local beds of sandstone, 

conglomerate, and volcanic ash. 

Terrace deposits yield small to large supplies to domestic and irrigation wells in southeastern Laramie County (Carpenter-Egbert-Pine Bluffs area), Wyo. Except for southeastern

Laramie County, terrace deposits generally are topographically high and drained of water.

Yields small to large supplies to domestic, stock, public supply (municipal), irrigation, and 

industrial wells. Most utilized aquifer of the High Plains aquifer system in Laramie County.

Yields small to moderate supplies to domestic, stock, and irrigation wells. Unit generally is 

less permeable than Ogallala Formation.

Yields small supplies to domestic and stock wells in some areas. Yields large supplies to 

domestic, stock, public supply (municipal), irrigation, and industrial wells locally in areas 

with coarse-grained deposits (sandstone and conglomerate) or secondary permeability 

development. Unit is principal bedrock aquifer in southeastern Laramie County.

Quaternary

White River Group3

or Formation

(Twr)

High Plains aquifer system4

Alluvial and 

terrace-deposit 

aquifers1

White River

aquifer/

confining unit4

Quaternary

unconsolidateddeposit aquifers1

Lower Tertiary

aquifer/

confining unit4

Upper Tertiary

aquifers

Alluvial and 

terrace deposits

(Qu) 

Geologic unit

(map symbol 

in parentheses)

Ogallala

Formation

(To)

Arikaree

Formation

(Ta)

Holocene 

and 

Pleistocene 

1

Considered part of High Plains aquifer system only where saturated and hydraulically connected laterally or vertically to 

underlying Tertiary aquifers. In this report, terrace deposits include older alluvial fan deposits in areas east of Carpenter.

2

Chadron Formation of White River Group likely late Eocene in age, based on dating of rocks north of Laramie County 

(Prothero and Swisher, 1992). 

Thickness in 

Laramie County, 

in feet

(from Lowry and 

Crist, 1967)

0–330

0–200 Terrace

deposits

Alluvium 0–85

0–450

0–500

Ogallala

aquifer

Arikaree

aquifer

Modified from Lowry and Crist, 1967; Crist and Borchert, 1972; Crist, 1980; 

Gutentag and Weeks, 1980; Cooley and Crist, 1981, 1994; Libra and others, 1981; 

Weeks and Gutentag, 1981; Gutentag and others, 1984; and Whitehead, 1996

3

Divided into Brule and Chadron Formations in parts of Laramie County.

4

White River Group or Formation considered an aquifer and part of High Plains aquifer system only where 

permeable (coarse-grained deposits or zones of secondary permeability). Functions as lower confining unit to 

High Plains aquifer system where impermeable.

WYOMING

SOUTH DAKOTA

NEBRASKA

COLORADO

A′

A

A A′

Not to scale

To

Cretaceous sedimentary rocks

Tertiary Ogallala Formation

Tertiary White River Group or Formation

Tertiary Arikaree Formation

Modified from Denson and Bergendahl, 1961

Precambrian

granitic and

metamorphic rocks

Map area

Figure 2. Simplified schematic showing relation of Tertiary geologic units composing the High Plains aquifer 

system, southeast Wyoming to Nebraska panhandle (A–A’).

10′ 105° 50′ 40′ 30′ 20′ 104°10′ 41°40′

30′

20′

10′

41°

0.1 to 99

100 to 199

200 to 299

500 to 599

600 to 699

700 to 799

800 to 899

300 to 399

400 to 499

EXPLANATION

Estimated saturated thickness, 

 March–June 2009, in feet

T. 12 N.

T. 13 N.

T. 14 N.

T. 15 N.

T. 16 N.

T. 17 N.

T. 18 N.

T. 19 N.

R. 70 W. R. 69 W. R. 68 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R. 61 W. R. 60 W.

Boundary of mapped data

Unsaturated or insufficient data

WYOMING

COLORADO

WYOMING

NEBRASKA

PLATTE COUNTY

LARAMIE COUNTY

GOSHEN COUNTY

ALBANY COUNTY

LARAMIE COUNTY

Base from Beartooth Mapping Inc. Digital Raster Graphics (DRG-E), 1982−84, 1:100,000

Universal Transverse Mercator projection, zone 12

North American Datum of 1927

LAND-SURFACE CONTOUR INTERVAL 10 METERS

NATIONAL GEODETIC VERTICAL DATUM OF 1929

0

0 5 10 15

10

20 KILOMETERS

5 15 20 MILES

Figure 4. Estimated saturated thickness of the combined Quaternary unconsolidated-deposit, Ogallala, and Arikaree aquifers in the High Plains aquifer system, March–June 2009, Laramie County, Wyoming.

Figure 5. Estimated saturated thickness of the combined Quaternary unconsolidated-deposit, Ogallala, and Arikaree aquifers, and White River aquifer/confining unit in the High Plains aquifer system, March–June 2009, Laramie County, Wyoming.

Printed on recycled paper

Generalized Potentiometric Surface of the High Plains Aquifer System,

March−June 2009, Laramie County, Wyoming

Egbert

50′ 40′ 30′ 20′ 104°10′ 105°00′ 10′

41°30′

20′

10′

41°00′

41°30′

20′

10′

50′ 40′ 30′ 20′ 104°10′ 105°00′ 10′

R. 68 W.

41°00′

WYOMING

NEBRASKA

PLATTE COUNTY

LARAMIE COUNTY

GOSHEN COUNTY

LARAMIE COUNTY

LARAMIE COUNTY

KIMBALL COUNTY

WYOMING

COLORADO

MONTANA

IDAHO

UTAH COLORADO

Map 

area

NEBRASKA SOUTH DAKOTA

Index map

High Plains 

aquifer system

WYOMING

5,850

5,750

5,900

5,950

5,500

5,600

5,650

5,700

5,850

5,750

5,400

6,050

5,200

6,200

5,350

6,250

6,300

6,400

6,400

6,450

5,150

5,100

5,050

5,000

6,450

6,500

4,950

6,550

6,500

6,650

4,850

6,700

5,200

4,750

4,700

5,050

6,750

6,700

6,800

6,600

5,000

6,450

5,050

6,200

6,000

6,550

6,550

6,500

5,100

6,150

6,600

6,450

6,500

6,650

5,250

6,650

6,750

6,100

6,350

6,300

6,250

6,150

6,100

6,050

6,000

5,900

5,850

5,800

6,400

6,550

6,600

6,650

6,800

6,700

6,600

6,350

6,150

6,100

6,050

6,000

5,950

5,900

5,800

5,700

5,650

5,550

5,450

5,350

5,300

4,800

4,900

5,250

5,150

5,100

5,000

5,150

6,400

6,350

6,300

6,250

6,200

6,150

6,100

6,050

5,150

5,200

5,100

5,050

5,300

5,250

5,400

5,450

6,250

6,350

6,300

6,250

6,200

6,150

6,100

6,000

5,950

5,800

5,600

5,550

5,500

5,150

5,200

5,250

5,300

5,350

5,400

5,450

6,127

5,078 5,085

5,075

5,220

5,168

4,940

6,459

5,525

5,068

6,040

8

6,532

28

5,539

97

6,498

92

6,503

214

5,093

7.7

6,097

9.9

6,178

5.2

6,030

86.6

5,601

83.7

6,584

58.5

6,724

62.7

6,069

94.4

6,377

93.3

5,572

87.9

5,394

46.8

4,975

87.5

6,498

93.9

5,748 15.7

5,595

44.9

5,457

57.4

5,407

48.5

5,162

52.2

5,124

25.4

5,435

34.4

5,134

8.04

6,122

6.56

5,881

126.4

5,424

301.4

5,074

298.4

6,417

167.5

5,338

212.4

5,368

226.3

5,339

215.6

5,143

252.9

5,147

276.7

4,961

123.1

6,142

148.3

5,559

166.9

5,313

116.9

5,103

187.6

6,412

9.34

6,621

170.4

5,632

146.2

5,249

142.9

5,169

125.5

6,394

207.1

6,361

101.9

6,148 139.2

5,951

100.6

5,450 8.96

5,076

6.34

6,334

3.96

6,088

9.92

6,002

4.82

5,170

9.39

5,466

61.88

5,776

97.02

5,793

86.08

5,569

67.99

5,460

62.01

5,528

69.07

5,451

75.21

5,375

23.69

4,911

57.74

6,387

18.28

6,437

35.89

6,594

32.12

6,093

57.15

5,778

53.92

5,883

22.08

5,640

20.95

5,564

54.58

5,642

76.26

5,669

50.25

5,490

52.24

5,546

36.64

5,295

93.67

5,396

13.18

4,995

12.33

4,883

30.04

4,865

39.73

4,920

36.09

4,944

33.94

4,861

69.05

4,793

17.41

4,825

46.42

4,791

56.74

6,503

82.73

6,707

54.98

6,793

11.02

6,184

98.19

5,562

73.73

5,393

42.62

5,365 57.03

5,263

69.69

6,100

86.49

5,401

24.82

6,570

17.06

6,603

72.68

6,737

93.31

6,277

65.46

6,115

64.02

5,986

88.76

5,733

21.46

5,647 16.62

5,498

90.64

5,461

92.17

5,568 93.31

5,492

93.34

5,565

56.75

5,120

88.84

5,211

80.18

5,142

86.61

5,028

67.51

5,044

55.46

5,067

95.26

5,040 83.84

5,035

52.31

5,113

62.06

5,118

44.74

5,176

86.39

6,356

82.94

6,343

63.62

6,271

59.93

6,420

98.69

6,245

16.44

6,154

23.27

6,139

33.39

6,222

34.35

6,300

85.63

6,244

74.87

5,782

98.06

5,602

67.17

5,465

97.49

5,473

54.24

5,481 45.13

5,261

77.19

5,395

28.73

5,156

26.21

5,242

66.88

5,145

38.95

5,153

28.09

5,110

34.31

5,126

54.06

5,039

65.38

5,050

60.08

5,010

56.49

5,009

52.97

5,024

40.18

5,042

-0.91

39.22 6,384

6,551

14.04

6,401

84.61

6,443

38.98

6,368

43.71

6,366

48.87

6,119

43.96

6,141

54.95

6,098

38.57

5,886

42.23

5,848

14.32

5,836

73.75

5,381

56.99

5,414

96.86

5,548

70.75

5,484 23.91

5,571

51.02

5,352

66.29

5,296 66.51

5,365

65.36

5,247

56.88

5,225

47.96

5,203

70.06

5,262

16.02

5,229

16.67

5,225

17.31

5,203

50.42

5,150

34.97

5,134

63.98

5,076

63.23

5,062

49.08

6,076

95.66

5,714 54.12

5,696

32.89

5,659

56.71

5,438

70.93

5,351

41.66

5,343

33.74

5,336

60.77

5,351 63.16

5,345

68.72

5,258

69.51

5,235

31.48

5,336

52.37

5,342

57.62

5,344

27.95

5,195

77.87

5,242

37.19

5,139

55.44

5,134

109.93

6,035

116.46

5,329

117.88

5,932

105.19

5,722

190.69

5,471

105.84

5,290

139.09

5,181

127.72

5,122

190.39

5,065

262.72

5,092

248.74

5,061

178.92

4,971

150.16

6,275

145.25

5,897

194.06

5,911

198.18

5,457

242.13

5,418

173.21

5,369

167.32

5,385

183.79

5,287

183.24

5,307

215.48

5,187

235.82

5,156

190.68

5,169

259.79

5,140

180.92

5,211

275.44

4,974

268.66

5,003

219.38

5,071

231.39

5,049

253.34

5,062

255.57

5,144

217.61

5,142

244.28

5,126

233.22

5,127

259.98

5,102

128.28

6,722

153.02

6,789

134.03

6,413

185.28

6,315

215.86

6,076

156.74

5,732

146.19

5,889

195.08

5,842

186.17

5,817

158.68

5,648

184.25

5,588

164.18

5,668

183.94

5,688

159.38

5,603 232.41

5,546

155.92

5,466

176.61

5,515

200.98

5,506

130.66

5,353

134.63

5,230

146.47

5,286

198.95

5,255

207.71

5,201

238.42

5,172

222.48

5,242

102.55

5,180

226.55

5,005

250.88

5,051

192.75

5,148

170.96

5,061

154.81

5,155

199.16

5,125

287.95

5,032

304.54

6,617

213.82

6,556

195.18

6,412

267.08

6,498

130.91

6,257

167.12

6,243

141.17

6,279

109.88

5,932

120.23

5,835

112.49

5,650 100.84

5,569

103.86

5,481

103.03

5,407

123.14

5,438

117.52

5,157

101.71

5,117

120.14

6,400

132.32

6,383

160.17

6,233

148.49

6,200

147.67

6,514

101.75

6,125

210.31

5,862 165.22

5,970

245.62

5,816

189.19

5,754

259.19

5,828

179.84

5,790

171.92

5,868

105.32

5,662

109.56

5,628

157.81

5,722

116.38

5,662

106.14

5,466

197.88

5,122

131.85

6,508

166.87

6,473

146.93

6,458

277.46

6,402

184.32

5,893

214.89

5,890

220.76

5,786

158.92

5,742

195.29

5,875

152.93

5,665

114.44

5,686

103.35

5,650

146.32

5,222

166.38

5,216

140.58

5,150

200.92

6,049

201.37

6,049

137.12

6,033

266.08

5,879

244.78

6,025

175.78

5,796

152.31

5,660

149.16

5,296

204.03

5,191

132.02

6,198

94.3

6,466

5,278

5,250

5,300

5,350

5,750

5,725

6,020

6,020 5,995

6,025 6,000

6,010

5,995

6,134

6,232

6,284

Qu

Tertiary Ogallala Formation

Tertiary White River Group or Formation

Mesozoic sedimentary rocks

EXPLANATION Base from Beartooth Mapping Inc. Digital Raster Graphics (DRG-E), 1982–84, 1:100,000

Universal Transverse Mercator projection, Zone 12

North American Datum of 1927

DESCRIPTION OF MAP UNITS

Geologic units

Quaternary unconsolidated deposits—Locally part of High 

 Plains aquifer system where saturated and hydraulically 

 connected laterally or vertically to underlying Tertiary units

To

Ta Tertiary Arikaree Formation

Twr

}

Qu

Index to geologic mapping

A Love and Christiansen, 1985

B Ver Ploeg and others, 2000

C Ver Ploeg and others, 1998

A

B C

9°

APPROXIMATE MEAN

DECLINATION, 2010 TRUE NORTH

MAGNETIC NORTH

5,000

 Quaternary unconsolidated deposits

 Tertiary Ogallala Formation

 Tertiary Arikaree Formation

 Tertiary White River Group or Formation

 Multiple geologic units of the High Plains aquifer system

0

0 1 2 4

1 2 4 6 8 10

6 8 10 12 14 16 18

12 14 16 18 20 MILES

SCALE 1:125,000

LAND-SURFACE CONTOUR INTERVAL 10 METERS

NATIONAL GEODETIC VERTICAL DATUM OF 1929

20 KILOMETERS

244.28

5,125.72

T. 12 N.

T. 13 N.

T. 14 N.

T. 15 N.

T. 16 N.

T. 17 N.

T. 18 N.

T. 19 N.

T. 12 N.

T. 13 N.

T. 14 N.

T. 15 N.

T. 16 N.

T. 17 N.

T. 18 N.

T. 19 N.

R. 70 W. R. 69 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R. 61 W. R. 60 W.

R. 70 W. R. 69 W. R. 68 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R. 61 W. R. 60 W.

Qu

Qu

Ta

To

To

Ta

Ta

Twr

Twr

Twr

Ta

Ta

To

Twr

}

|

Qu

}

}

Qu Mz

|

Twr

Twr

Twr

Qu

}

|

Twr

}

To

Ta

To

Qu

Qu

Ta

Qu

Qu

Qu

5,078

Potentiometric contour—Shows altitude at which water level would have stood 

 in tightly cased wells, March–June 2009. Dashed where inferred or 

 approximately located. Hachures indicate depression. Contour interval 50 feet. 

 Datum is National Geodetic Vertical Datum of 1929 (NGVD 29)

Spring and number—Tail points in direction of flow. Number is altitude of 

 land surface, in feet above NGVD 29

Well and number—Number above bar is depth to water, in feet below land 

 surface. Number below bar is altitude of water surface. Negative value indicates 

 water level above land surface. Datum is NGVD 29

Well completed in:

To

Twr

Pz

Qu

}

|

Qu

Qu

To

To

Qu

Twr

To

To

Ta

Twr

Twr

Qu

Qu

To

To

Qu

Qu

Twr

Qu

Ta

To

Qu

To

Regional geologic 

units of the High 

Plains aquifer 

system

LARAMIE MOUNTAINS

LARAMIE MOUNTAINS

Mesozoic and Paleozoic sedimentary rocks

Paleozoic sedimentary rocks

Precambrian granitic and metamorphic rocks

}|

|

}|

}|

}|

}|

=

=

=

=

=

=

=

CHEYENNE

Crow

Creek

Lodgepole

Creek

Creek

Horse

Creek

Creek

Creek

Horse

Lodgepole

Crow

Creek

Carpenter

Pine Bluffs

Chugwater

Figure 3. Estimated depth to water in the High Plains aquifer system, March–June 2009, Laramie County, Wyoming.

Table 1. Summary of groundwater-level measurements and well depths, High Plains aquifer system, 

March–June 2009, Laramie County, Wyoming.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Characteristic Number of 

measurements Minimum Median Maximum

All aquifers

Water level1, in feet below land surface 330 2-0.91 93.50 304.54

Water-level altitude, in feet above 

NGVD 29

330 4,790.58 5,499.60 6,793.02

Well depth, in feet below land surface 292 15.5 200 815

Quaternary unconsolidated-deposit aquifers

Water level1, in feet below land surface 14 4.82 57.51 77.87

Water-level altitude, in feet above 

NGVD 29

14 4,975.20 5,277.00 5,639.92

Well depth, in feet below land surface 14 30 93.50 205

Ogallala aquifer

Water level1, in feet below land surface 135 2-0.91 98.69 298.40

Water-level altitude, in feet above 

NGVD 29

135 4,973.56 5,888.81 6,793.02

Well depth, in feet below land surface 112 15.5 208 575

Arikaree aquifer

Water level1, in feet below land surface 76 20.95 168.95 287.95

Water-level altitude, in feet above 

NGVD 29

76 4,961.30 5,366.49 6,100.31

Well depth, in feet below land surface 68 55 268.26 500

White River aquifer/confining unit

Water level1, in feet below land surface 105 6.56 60.08 304.54

Water-level altitude, in feet above 

NGVD 29

105 4,790.58 5,215.62 6,788.98

Well depth, in feet below land surface 98 22 132.50 815

1

Measurements were made with a calibrated steel or electrical tape (Cunningham and Schalk, 2011).

2

Negative value indicates water level above land surface.

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

WYOMING STATE ENGINEER’S OFFICE

Scientific Investigations Map 3180

Generalized Potentiometric Surface, Estimated Depth to Water, and Estimated Saturated Thickness of the High Plains Aquifer System, March–June 2009, Laramie County, Wyoming

By

Timothy T. Bartos and Laura L. Hallberg

2011

Introduction

The High Plains aquifer system, commonly called the High Plains aquifer in many publications, is a nationally important water resource that underlies a 111-million-acre area 

[173,000 square miles (mi2)] in parts of eight States: Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming (McGuire and others, 2003). Through irrigation of 

crops with groundwater from the High Plains aquifer system, the area that overlies the aquifer system has become one of the world’s major agricultural regions. In addition, the aquifer system also 

serves as the primary source of drinking water for most residents of the region. In 2000, the High 

Plains aquifer system had an estimated 2,980 million acre-feet of drainable water (water in the 

aquifer system that would drain by gravity and generally can be withdrawn by wells) in storage, 

making it one of the largest aquifers or aquifer systems in the world (McGuire and others, 2003).

The High Plains aquifer system underlies an area of 8,190 mi2 in southeastern Wyoming 

(Gutentag and Weeks, 1980). Including Laramie County, the High Plains aquifer system is present 

in parts of five counties in southeastern Wyoming (see index map). The High Plains aquifer system 

underlies 8 percent of Wyoming, and 5 percent of the aquifer system is located within the State 

(Gutentag and Weeks, 1980). Based on withdrawals for irrigation, public supply, and industrial use 

in 2000, the High Plains aquifer system is the most utilized source of groundwater in Wyoming 

(Boughton and others, 2006, fig. 4).

With the exception of the Laramie Mountains in western Laramie County (areas shaded with 

green, blue, and purple on map, indicating Mesozoic and older rocks), the High Plains aquifer 

system is present throughout Laramie County. In Laramie County, the High Plains aquifer system is the predominant groundwater resource for agricultural (irrigation), municipal, industrial, 

and domestic uses. Withdrawal of groundwater for irrigation (primarily in the eastern part of the 

county) is the largest use of water from the High Plains aquifer system in Laramie County and 

southeastern Wyoming (Boughton and others, 2006).

Groundwater-level declines, associated with localized high-use areas in the High Plains 

aquifer system in Laramie County, have been noted as far back as the 1940s (Lowry and Crist, 

1967). In fact, in response to groundwater-level declines (primarily due to irrigation withdrawals) 

in some areas in southeastern Wyoming, special “areas” of the aquifer system were selected for 

increased groundwater regulation. In Laramie County, a specially regulated aquifer area known as 

the “Laramie County Control Area” was created in 1981 by the Wyoming Board of Control (JR 

Engineering LLC and others, 2008). The Laramie County Control Area (not shown) comprises 

much of the county, but generally includes the High Plains aquifer system from about Interstate 25 

in west-central Laramie County eastward to the Wyoming-Nebraska State line. For the Laramie 

County Control Area, an Advisory Board reviews and makes water-administration recommendations to the Wyoming State Engineer’s Office (WSEO) concerning any development of new wells, 

enlargements of existing permitted wells, or placement of new lands under irrigation within the 

Control Area.

Continued interest in groundwater levels in the High Plains aquifer system in Laramie County 

prompted a study by the U.S. Geological Survey (USGS) in cooperation with the WSEO to update 

the potentiometric-surface map of the aquifer system in Laramie County. Groundwater levels were 

measured in wells completed in the High Plains aquifer system and used to construct a map of the 

potentiometric surface of the High Plains aquifer system. The potentiometric surface of an aquifer 

is equal to the altitude at which water will rise in tightly cased wells open to a given point in that 

aquifer (Lohman and others, 1972). In areas where the aquifer is unconfined, the potentiometric 

surface is equal to the water-table altitude. The potentiometric-surface map provides a tool for 

evaluating groundwater flow directions and hydraulic gradients in the High Plains aquifer system. 

Purpose and Scope

The primary purpose of this map is to present the generalized potentiometric surface of the 

High Plains aquifer system in Laramie County, Wyoming. Groundwater levels used to construct 

the potentiometric surface were measured between March and June 2009, but most groundwater 

levels were measured between March and May. In addition, the hydrogeologic units of the High 

Plains aquifer system in Laramie County are briefly described, along with depth to water and estimated saturated-thickness maps created using the potentiometric-surface map presented herein.

Previous Investigations

Excluding regional maps, two county-wide potentiometric-surface maps of the High Plains 

aquifer system in Laramie County have been constructed previously (Lowry and Crist, 1967, pl. 2; 

Crist, 1980, pl. 4). Groundwater-level measurements used to construct the potentiometric-surface 

map in Crist (1980) also were utilized in the fence diagrams of the High Plains aquifer system 

constructed by Cooley and Crist (1981). Crist and Borchert (1972, fig. 7) constructed two potentiometric-surface maps (representing March and September 1971) for the aquifer system in southeastern Laramie County (Carpenter-Egbert-Pine Bluffs area). JR Engineering LLC and others (2008, 

p. 6–11 to 6–14) modified parts of the potentiometric-surface map of Crist (1980) with more recent 

groundwater levels to represent predevelopment (before 1943) and two later (1994 and 2004) time 

periods. In addition, numerous local-scale investigations within the county (not listed herein) have 

produced potentiometric-surface maps of the aquifer system for areas of small geographic extent.

Acknowledgments

The authors would like to thank all the people who assisted with this study, measured 

groundwater levels, and assisted with preparation of the report. Lisa Lindemann and John Harju 

of the WSEO are gratefully acknowledged for their support of this study. George Moser, Nick 

Leventis, James Neely, and Ben Running with the WSEO, and Greg Boughton, Mike Sweat, Seth 

Davidson, and Kathy Foster with the USGS measured groundwater levels throughout Laramie 

County. Special thanks are given to Victor Spencer of the Cheyenne Board of Public Utilities who 

kindly provided groundwater levels from monitoring wells located within the City of Cheyenne 

well fields. The authors thank the many public and private landowners of Laramie County who 

provided information and access to their water wells for measurements. Colleague reviews by 

Virginia McGuire (USGS) and Laura Bexfield (USGS) improved the quality of the manuscript. 

George Moser and Jeremy Manley (WSEO) provided helpful comments. Suzanne Roberts (USGS) 

is thanked for creating the illustrations and performing layout work.

Description of Study Area

Laramie County, in the southeastern corner of Wyoming, includes an area of 2,709 mi2. The 

county includes parts of the southern Rocky Mountains physiographic province (Laramie Mountains that extend along the western edge of the county) and Great Plains physiographic province 

(most of the county) described by Fenneman (1946). The topography of the area east of the 

Laramie Mountains within the Great Plains physiographic province, which is most of the county, 

generally is a “high eastward-sloping” and “gently rolling surface of only moderate relief” underlain by Tertiary sedimentary rocks (Lowry and Crist, 1967, p. 6). Several prominent escarpments 

noticeably affect topography, particularly in the northern and southeastern parts of the county. 

Small eastward-flowing perennial, intermittent, and ephemeral streams drain the county, only two 

of which (Horse and Chugwater Creeks) are perennial throughout their courses (Lowry and Crist, 

1967). The climate, which is characteristic of the northern Great Plains, is semiarid with large temperature variations, cold winters, low precipitation, frequent winds, low humidity, and high evaporation. Mean annual precipitation (snow and rain) ranges from about 14 to 18 inches in the central 

and eastern parts of the county to as much as 24 inches in the Laramie Mountains on the western 

edge of the county (JR Engineering LLC and others, 2008, unnumbered figure, p. 4–1). Excluding 

the Laramie Mountains, land use/land cover is predominantly rangeland and agricultural land. The 

population of Laramie County in 2010 was 91,738 (U.S. Census Bureau, 2011).

Hydrogeologic Setting

In Laramie County, the primary aquifers are the unconsolidated Quaternary alluvial and terrace deposits, the Tertiary Ogallala and Arikaree Formations, and the Tertiary White River Group 

or Formation; these aquifers are part of the High Plains aquifer system (fig. 1). An aquifer system 

consists of two or more aquifers, commonly vertically stacked, that are grouped together because 

of physical connection or sharing of similar geologic and hydrologic characteristics that are best 

described and studied together. Hydraulic connection among the Quaternary unconsolidateddeposit, Ogallala, and Arikaree aquifers, and the White River aquifer/confining unit varies locally, 

but regionally they are in sufficient hydraulic connection to compose a regional aquifer system 

(Crist, 1980; Cooley and Crist, 1981, 1994; Gutentag and Weeks, 1980; Avery and Pettijohn, 1984; 

Libra and others, 1981; Weeks and Gutentag, 1981; Gutentag and others, 1984). In many publications, the High Plains aquifer system in southeastern Wyoming is informally referred to as the 

“Tertiary aquifer” or “Tertiary aquifer system.”

The aquifers contained in Tertiary geologic units are vertically stacked, although not all are 

present throughout Laramie County due to erosion (see geologic units on map and shown vertically stacked on schematic diagram in fig. 2). Consequently, wells completed in the High Plains 

aquifer system in Laramie County can obtain water from one or more of these aquifers, depending 

on well location and construction (some wells are completed in more than one aquifer).

Regionally, including Laramie County, the High Plains aquifer system is defined as an 

unconfined or “water-table” aquifer or aquifer system (Crist, 1980; Cooley and Crist, 1981, 1994; 

Gutentag and Weeks, 1980; Weeks and Gutentag, 1981; Gutentag and others, 1984). However, 

locally confining or semi-confining conditions occur in many places within Laramie County (for 

example, see Cooley and Crist, 1994).

Alternating episodes of deposition and erosion created the Cenozoic sedimentary geologic 

units composing the High Plains aquifer system. The thickness and lithology of these geologic 

units in Laramie County are summarized in figure 1. Quaternary unconsolidated deposits (alluvium 

and terrace deposits) were deposited by eastward-flowing streams. Alluvium was deposited from 

the erosion of the uplift to the west or in-place erosion of Tertiary geologic units composing the 

High Plains aquifer system. Terrace deposits are erosional remnants of alluvium that were deposited along former or current stream valleys. The Ogallala Formation is a complex sequence of cuts 

and fills composed mostly of stream-laid sediments with minor amounts of volcanic ash (Stanley, 

1976; Diffendal, 1984, and references therein; Swinehart and others, 1985, and references therein). 

In contrast, the Arikaree Formation and White River Group or Formation are mostly composed 

of valley fills of windborne volcanic material transported into Wyoming from volcanoes in States 

located predominantly to the west (Stanley, 1976; Swinehart and others, 1985, and references 

therein). Some stream-laid sediment also occurs in the fills, most commonly at the bases of these 

two geologic units. Paleosols (fossil soils) occur in all three Tertiary geologic units. All three 

Tertiary geologic units slope gently to the east with dips of no more than 1 to 2 degrees (Ver Ploeg 

and others, 1998, 2000).

Unconsolidated sand and gravel beds of the Ogallala Formation yield water more readily than 

the sandstone beds in the Arikaree Formation. The consolidated siltstone and sandstone beds of 

the White River Group or Formation yield highly variable volumes of water; yields are greatest 

where the permeability of the geologic unit has been increased by secondary permeability development from fractures, joints, and solution openings (Lowry, 1966; Lowry and Crist, 1967; Crist 

and Borchert, 1972). The Ogallala and Arikaree Formations generally are permeable and defined 

as aquifers throughout Laramie County, whereas the White River Group or Formation is only 

permeable and defined as an aquifer in areas with coarse-grained deposits or secondary permeability development. Where impermeable, the White River Group or Formation is defined as a basal 

confining unit to the High Plains aquifer system (fig. 1).

Potentiometric Surface

The generalized potentiometric surface of the High Plains aquifer system in Laramie County, 

shown on the map, was constructed on the basis of groundwater levels measured in wells during 

March–June 2009. Groundwater levels in wells located within irrigation areas in Laramie County 

generally were measured first, prior to the beginning of the 2009 irrigation season. The potentiometric surface represents water-level altitudes and feet above the National Geodetic Vertical 

Datum of 1929 (NGVD 29). 

The potentiometric surface of the High Plains aquifer system was mapped by contouring altitudes of groundwater levels measured in 330 wells completed in Quaternary and Tertiary geologic 

units composing the aquifer system (see map; table 1). Of the 330 wells for which a groundwater 

level was used to construct the potentiometric surface, 94 were used primarily for domestic use; 

83 were primarily for stock use; 55 were primarily for irrigation use; 41 were unused; 31 were for 

monitoring purposes; and the remaining 26 wells were used for other miscellaneous purposes. The 

land-surface altitude of a spring in an outcrop area is approximately equal to (or slightly higher 

than) the water-table altitude at that location, and thus several spring locations also were used to 

construct the potentiometric surface. The altitudes of perennial streams and associated perennial 

reaches known to be in hydraulic connection with the High Plains aquifer system (as identified 

by Lowry and Crist, 1967; Crist and Borchert, 1972; Crist, 1980; and Cooley and Crist, 1981) 

also were used as control for mapping the potentiometric surface. The geologic unit(s) of the 

High Plains aquifer system that a measured well was completed in were estimated based on well 

location, well depth, geologic or well logs, and comparisons with information in previous publications; the unit(s) are indicated on the map by use of different colored symbols. Groundwater 

levels measured to construct the potentiometric surface and available well depths for measured 

wells are summarized by aquifer in table 1; groundwater levels and depths measured for wells 

completed in multiple geologic units of the High Plains aquifer system (see map) were assigned to 

one primary geologic unit (aquifer) for summary purposes in table 1. The water-level altitudes and 

depth to water measurements shown on the map, as well as additional ancillary information for all 

measured wells, are available from the Groundwater Site Inventory database of the USGS National 

Water Information System database at http://waterdata.usgs.gov/wy/nwis/gw.

Groundwater moves from high altitudes to lower altitudes and generally in a direction that 

is perpendicular to the potentiometric contours in the direction of the slope of the potentiometric 

surface (hydraulic gradient). In the High Plains aquifer system in Laramie County, groundwater generally moves from west to east, but this pattern of flow is altered locally by groundwater 

divides, and by groundwater discharge to streams (see map). The altitude of the potentiometric 

surface declines from about 6,800 feet (ft) in western Laramie County to about 5,000 ft in eastern 

Laramie County. Discharge is by the movement of water to seeps and springs, streams, evapotranspiration, and withdrawal from wells. Some groundwater also flows out of the county as underflow, 

especially in the Quaternary unconsolidated-deposit aquifers (Rapp and others, 1953; Bjorklund, 

1959; Lowry and Crist, 1967). 

Several surface-drainage systems locally affect the configuration of the potentiometric 

surface, most notably Chugwater Creek, Horse Creek, Lodgepole Creek, and the upper reaches of 

Crow Creek (see map). Potentiometric contours in the immediate vicinity of streams can indicate 

gaining streams by pointing in an upstream direction (potentiometric surface above water in the 

stream) or losing streams by pointing in a downstream direction (potentiometric surface below 

water in the stream). Chugwater and Horse Creeks generally gain water from the High Plains 

aquifer system throughout their reaches, and both are the only streams perennial throughout their 

courses in the county; all other streams are intermittent, many alternating between gaining or 

losing water to the aquifer system (Lowry and Crist, 1967; Cooley and Crist, 1981). Depending 

upon the reach, Lodgepole Creek either gains water from or loses water to the High Plains aquifer 

system (Lowry and Crist, 1967). Water-level contours along Crow Creek show that the stream 

generally gains water from the High Plains aquifer system west of Cheyenne and loses water to the 

aquifer system in the reaches east of the city. 

Depth to Water

A map showing the estimated depth to water in the High Plains aquifer system in Laramie 

County during March–June 2009 (fig. 3) was constructed using a geographic information system 

to determine the vertical distance between the land-surface altitude (U.S. Geological Survey, 2010) 

and the potentiometric-surface altitude. Depth to water in the High Plains aquifer system ranged 

from less than 50 ft to more than 300 ft. Depth to water was shallowest (0 to 50 ft) beneath stream 

valleys and other topographically low areas.

Saturated Thickness

Two maps were constructed showing the estimated saturated thickness of different combinations of geologic units composing the High Plains aquifer system in Laramie County during 

March–June 2009. The saturated thickness is the vertical distance between the potentiometric 

surface and the base of the geologic units composing the individual aquifers within the system or 

the entire aquifer system. The first map (fig. 4), showing the estimated saturated thickness of the 

combined Quaternary unconsolidated-deposit, Ogallala, and Arikaree aquifers, was constructed 

using a geographic information system to determine the vertical distance between the altitude of 

the potentiometric surface of the aquifer system and the altitude of the base of the Arikaree Formation (modified and updated from contours showing the top of the White River Formation in Lowry 

and Crist, 1967, pl. 2). The estimated saturated thickness of the combined Ogallala and Arikaree 

aquifers ranged from less than 1 foot to almost 500 ft. 

The second map (fig. 5), showing the estimated saturated thickness of the combined Quaternary unconsolidated-deposit, Ogallala, and Arikaree aquifers, and the White River aquifer/

confining unit (all units composing the High Plains aquifer system), was constructed by using 

a geographic information system to determine the vertical distance between the altitude of the 

potentiometric surface of the aquifer system and the altitude of the base of the White River Group 

or Formation (modified and updated from Crist, 1980, pl. 2). The estimated saturated thickness of 

the combined Quaternary unconsolidated-deposit, Ogallala, and Arikaree aquifers, and the White 

River aquifer/confining unit ranged from less than 1 foot to almost 900 ft.

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Suggested citation: Bartos, T.T., and Hallberg, L.L., 2011, Generalized potentiometric surface, estimated 

depth to water, and estimated saturated thickness of the High Plains aquifer system, March–June 2009, 

Laramie County, Wyoming: U.S. Geological Survey Scientific Investigations Map 3180, 1 sheet 

[http://pubs.usgs.gov/sim/3180/].

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