Water in the Dakota and 

Purgatoire Formations in Otero 

County and the Southern Part 

of Crowley County, Colorado _J|

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1669-P

Prepared in cooperation with the 

Colorado Water Conservation Board
Water in the Dakota and 

Purgatoire Formations in Otero 

County and the Southern Fart 

of Crowley County, Colorado

By WILLIAM G. WEIST, JR.

CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES 

GEOLOGICAL SURVEY WATER-SUPPLY PAPEF 1669-P

Prepared in cooperation with the 

Colorado fPater Conservation Board

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.G., 20402
CONTENTS

	Page 

Abstract________________________________________________________ PI

Introduction...___________________________________________________ PI

Geology_______________._____________________ P3

Stratigraphy._________________________________________________ P3

Structure___________________________________ P3

Occurrence of soft water__________________________________________ P4

Soft and hard water___________________________________________ P4

Principal aquifers____________________________________________ P5

Recharge areas________________________________________________ P9

Development and utilization________________________________________ P10

History of development________________________________________ P10

Present utilization_____________________________________________ P10

Stock and domestic supplies_-_____-___---__________-__-_-__ Pll

Municipal supplies_______________________________________ Pll

Private water associations._________________________________ P12

Water hauling_____________________________ P12

Industrial supplies.________________________________________ P12

Chemical quality of water samples___________________________________ P13

Conclusions_____________________________________________________ P16

References cited___________________________________________________ P16

ILLUSTRATIONS

Page

FIGURE 1. Map of Colorado showing the location of the report area pnd

geologic structural features_____________________--___-__ P2

2. Map showing approximate depth to the top of the Dakota

Sandstone.___________________________________________ P6

3. Map showing approximate depth to the piezometric surface of

water in the Dakota Sandstone, 1959-60-________________ P8

4. Fluctuations of the water level in a Dakota well___________ P9

5. Analyses of ground water_______________________________ P15

TABLE

Page

TABLE 1. Generalized section of the geologic units discussed_________ P4

IT
CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

WATER IN DAKOTA AND PURGATOIRE FORMATIONS IN 

OTERO COUNTY AND THE SOUTHERN PAFT OF 

CROWLEY COUNTY, COLORADO

By WILLIAM G. WEIST, JR.

ABSTRACT

The hardness of available shallow ground water in Otero County and in the 

southern part of Crowley County generally exceeds 1,000 parts per million, 

and the water requires treatment for most uses. To obtain a supply of softer 

water, wells have been drilled into the Dakota Sandstone and the Cheyenne 

Sandstone Member of the Purgatoire Formation, both Early Cretaceous in age. 

These aquifers underlie most of the area at depths from 0 to 2,000 feet and 

have a general regional dip northward into the Denver Basin. More than 

350 wells have been drilled into the aquifers in this area to obtain water 

for stock, domestic, and industrial purposes and for public supply.

The aquifers are recharged in areas where they crop out or are overlain 

by sand, principally to the south and west of Otero County. Because water 

in the aquifers is generally under pressure, it rises above the top of the aquifer 

in wells penetrating it; at least 20 wells in the area flow. Yields from wells 

tapping the aquifers range from 4 to 75 gpm (gallons per minute). Flows as 

great as 50 gpm have been obtained.

Water in the aquifers is commonly soft and of good chemical quality. There 

appears to be little difference in quality of water from the two aquifers.

Most residents and drillers know that soft water can be obtained from wells 

throughout most of the area described in this report, but many are not aware 

of certain factors related to the development of this water. This report 

should be of value in further developing the sources of soft water by showing: 

(a) The approximate depth of a well needed to tap these supplies, (b) the 

range in yields that may be expected, (c) the range in chemical quality that 

may be expected, (d) the depth to which water will rise in wells, and (e) 

information on the factors affecting the durability of the supply.

INTRODUCTION

This report discusses present knowledge of the occurrence, duality, 

and development of soft-water supplies in Otero County and southern 

Crowley County, Colo. The investigation was begun in Jul^ 1959

Fl
P2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

by the U.S. Geological Survey in cooperation with the Colorado 

Water Conservation Board, and was done under the supervision of 

E. A. Moulder, district engineer in charge of the Survey's groundwater investigations in Colorado.

The area of 1,500 square miles covered by this investigation is in 

southeastern Colorado (fig. 1), and comprises all of Tps. 21-27 S.,

FIGDKB 1. Map of Colorado showing the location of the report area and the major geologic

structural features.

Rs. 54-59 W. It is part of the Colorado Piedmont section of theGreat Plains physiographic province. Altitudes range from about 

5,200 feet along the western boundary of the report area to about 

4,000 feet in the valley of the Arkansas River at the eastern boundary 

of the area. The Arkansas River and its tributaries drain the region 

and, in general, the land surface slopes toward the river. The mean 

annual precipitation is 11 to 14 inches. Irrigation with surface 

water is practiced extensively in the Arkansas Valley, and ranches 

occupy most of the remainder of the area. The population of the 

two counties according to the 1960 census was 28,106. Most of the 

industries are related to agriculture and are in La Junta, Fowler, 

Rocky Ford, and Cheraw.
WATER IN DAKOTA AND PURGATOIRE FORMATIONS P3

Ground water is available from surficial deposits at deaths less 

than 100 feet throughout most of the area. Yields from wells are 

generally small except along the Arkansas River and some of its 

tributaries where large supplies can be obtained from the alluvium 

and low terraces along the river. However, most of this water is 

very hard and has a high sulfate content that makes it undesirable 

for most domestic, municipal, and industrial uses.

There is considerable interest in the availability of sol4' water, 

because shallow water is not available in some places and, where 

present, is generally very hard.

Water that generally is soft or softer than other available supplies 

and is better suited for domestic and industrial uses can be obtained 

from wells tapping the Dakota Sandstone and the Cheyenre Sandstone Member of the Purgatoire Formation of Early Cretaceous age, 

which underlie most of this area.

GEOLOGY

STRATIGRAPHY

The geologic units exposed in Otero County and the southerr part of 

Crowley County range from the Morrison Formation of Late Jurassic 

age to dune sand and alluvium of Recent age. This report, however, 

is concerned only with the principal artesian aquifers, the Cayenne 

Sandstone Member of the Purgatoire Formation, the Dakot'* Sandstone, and the formations immediately above and below then. The 

thickness of these formations, their physical characteristics, and their 

water-bearing properties are described in table 1.

STRUCTURE

The relation of the report area to three major geologic structural 

features of southeastern Colorado is shown on figure 1. To the east 

is the Las Animas arch; to the southwest is the Apishapa uplift; to 

the northwest is the axis of the Denver Basin; and to the north is 

the main part of the Denver Basin. Consequently, throughout most 

of the area the consolidated beds dip to the north or northwest into 

the Denver Basin. The southwestern part of Otero County is close 

to the Apishapa uplift and, in this area, the consolidated 1 -^is, in 

general, dip northeast away from the uplift. The dips are generally 

very slight, but local structural features cause very abrupt steepening 

or change in the direction of the dip.

686-165 63-
P4 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES 

TABLE 1. Generalized section of the geologic units discussed

System

Cretaceous

Jurassic

Series

Upper Cretaceous

Lower Cretaceous

Upper 

Jurassic

Formation

Qraneros 

Shale

Dakota 

Sandstone

Purgatoire Formation

Morrison Formation

Member

Kiowa

Shale

Cheyenne 

Sandstone

Thickness 

(feet)

90-200

7&-140

50-130

70-110

125-300

Physical character

Gray to black platy 

and fissile shale containing thin beds of 

bentonite; thin limestone beds in lower 

part. Transition 

zone of several feet 

of alternating sandstone and shale at 

base.

White to brown finegrained thin-bedded 

to massive sandstone; contains beds 

of gray to black 

sandy shale. Mostly quartz sand and 

limonite, calcite, or 

silica cement in varied amounts; hard 

to friable; forms 

cliffs and ledges; 

some lenticular beds 

and crossbedding; 

locally conglomeratic.

Gray to black platy 

calcareous shale; in 

places very sandy; 

contains some beds 

of brown finegrained sandstone.

Massive white to buff 

fine- to coarsegrained sandstone; 

poorly cemented 

and friable; some 

lenses of conglomerate in lower part.

Red, green, gray, and 

brown shale containing thin beds of 

sandstone and limestone; thin layers of 

chert at base.

Water-bearing 

properties

Relatively impermeabh. Not known to 

yieM water to weUs 

in area. Acts as confining bed for Dakota 

Sardstone.

Mod^rately porous; 

yields adequate 

wa*er for stock and 

domestic use. In 

sone areas yields 

enough water for 

municipal and industrial supplies. Water 

is soft but contains 

iron and sulfur.

Relatively impermeable. Not known to 

yield water to wells 

in area. Acts as confining bed between 

Dakota and Cheyen">e Sandstone 

Member.

Yields adequate water 

for stock and domestic use. In some 

anas yields enough 

water for municipal 

and industrial suppl'es.

Shades are relatively 

brnermeable. Some 

sandstone layers 

yi3ld small amounts 

of water for stock and 

domestic use.

Numerous small, nearly vertical faults are found in the more resistant beds. A few faults can be traced for a mile or more, but most 

lose their identity in beds of shale. Displacement along the faults 

is usually only a few feet.

OCCURRENCE OF SOFT WATER 

SOET AND HARD WATER

The adjectives "hard" and "soft" are often used to describe water, 

but they lack exactness and may have different connotations to different people. In an area such as New England, where the water is 

commonly low in dissolved solids, water having a hardnes-s of 100 ppm 

(parts per million) might be considered "very hard," whereas the
WATER IN DAKOTA AND PURGATOIRE FORMATIONS P5

same water in an area such as Arizona, where the water is generally 

high in dissolved solids, might be considered "soft."

The hardness of water classification of Collins, Lamar, and Lohr 

(1934, p. 17-18) has been generally accepted. Under this classification, water having a hardness of 60 ppm or less is considered "soft." 

However, water with a hardness near 60 ppm may have to be softened 

for some industrial uses. Water containing 61 to 120 ppm of hardness 

is "moderately hard" and will have to be softened for many industrial 

uses; it may be softened for household use. Collins, Lamar, and Lohr 

report, that it is customary to reduce the hardness of municipal supplies 

to less than 120 ppm. Water having a hardness of 121 to 180 ppm is 

considered "hard" and generally is softened for most uses. Water 

having a hardness of more than 180 ppm is considered "very hard."

The alkaline-earth metals, calcium and magnesium, are the principal 

constituents that cause hardness of water. Hardness also is caused 

by aluminum, iron, manganese, strontium, zinc, and free acid, but 

these generally are present in water only in very small amounts. It 

follows, therefore, that hard water will have a much higher calcium 

and magnesium content than soft water.

Most of the readily available shallow water in Otero County and 

in the southern part of Crowley County has a hardness of 1,000 ppm 

or more. Thus, water from the Dakota Sandstone is soft by comparison even though it may have a hardness as great as 400 ppm.

PRINCIPAL AQUIFERS

The Dakota Sandstone and the Cheyenne Sandstone Member of the 

Purgatoire Formation are the principal formations in Otero and 

Crowley Counties known to contain soft water. These units consist of 

sandstone, which in most areas is interbedded with shale. The 

Dakota Sandstone ranges in thickness from 75 to 140 feet, and the 

Cheyenne Sandstone Member ranges in thickness from 70 to 110 feet. 

The two sandstone units are separated by the Kiowa Shale Member, 

a black shale that in places is very sandy and that ranges in thickness 

from 50 to 130 feet.

These formations underlie all of Otero and southern Crowley 

Counties except parts of the southeast corner of Otero County where 

the Purgatoire River and its tributaries have cut through to the 

Morrison Formation, which underlies the Cheyenne Sandstone Member. Figure 2 shows the general area of outcrops of the Purgatoire 

Formation and the Dakota Sandstone and the approximate depth 

to the top of the Dakota Sandstone elsewhere in the area.

Below the Cheyenne Sandstone Member in this area are beds of 

sandstone of Triassic and Jurassic age that may contain potable water.

686-165 2 63
P6 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Base modified from maps prepared 

by the Army Map Service

Hydrology by William G. Weist, Jr., 1960. 

Geology from geologic map of Colorado 

(U.S. Geological Survey) 

EXPLANATION

 see 

Well

Number incJtcofes depth, in 

feel, to the top of the Dofcota 

Sandstone

Approximate areas 

of outcrop of the 

Dakota Sandstone 

and the Purgatoire

Formation

Appr 

wh 

Sa 

Pu

oximate areas 

ere the Dakota 

ndstone and the 

rgatoire Formation have been

eroded away

1O MILES 

I

CONTOUR INTERVAL 100 FEET

FIGURE 2. Map of report area showing approximate depth to the top of the 

Dakota Sandstone.
WATER IN DAKOTA AND PURGATOIRE FORMATIONS P7

These beds are known to contain soft water in other parts of Colorado 

and New Mexico. Potable supplies of hard water are sometimes 

obtained from lenses of sandstone in the Morrison Formation, but 

this is the only known source of potable water below the Cheyenne 

Sandstone Member in the area.

Water obtained from beds below the Morrison Formation probably 

would not be potable. Because the beds lie at fairly great depths, 

the water is very likely to be highly mineralized. Darton (1906, p. 

53-54) reports that a well drilled at Manzanola penetrated several 

beds containing water in a zone 1,655 to 2,110 feet deep, which is 280 

to Y35 feet below the base of the Cheyenne Sandstone Member. Darton 

reports the water was "too impure for use." Another well at Bloom 

reached water 600 feet below the base of the Cheyenne Sandstone 

Member. This water also was of poor quality. In 1961 a deep well 

was drilled at Las Animas, Colo., (19 miles east of La Junta) to test 

the deeper formation. Samples of water from various beds below 

the Morrison Formation were too highly mineralized for most uses.

Because the two water-bearing units are confined by underlying and 

overlying beds of fairly impermeable shale, the water in the two 

sandstones is under artesian pressure nearly everywhere, and rises 

above the level at which it is found, and in some places wells flow 

at the surface. The imaginary surface to which the water will rise 

under artesian pressure is called the "piezometric surface." This 

surface does not remain fixed but moves up and down in response to 

fluctuation of the artesian pressure, as is shown by changes in the water 

level in a well. Figure 3 shows the approximate depth to the piezometric surface of water in the Dakota Sandstone in the area as it was 

measured or reported during the summers of 1959 and 1960.

The level of the piezometric surface is gradually declining, especially in areas such as La Junta and Cheraw where many wells tap 

the artesian aquifers. The flow of many wells has decreased or even 

stopped. A few well owners have reported that they have had to 

lower their pumps to get an adequate supply of water. This decline 

of fche piezometric surface probably is due to the reduction in artesian 

head caused by the withdrawal of water from the increasing number 

of wells tapping these aquifers. Figure 4 shows the fluctuations of 

the water level in an observation well tapping the Dakota Sandstone 

south of La Junta.

Although the piezometric surface is slowly declining, the aquifers 

are not necessarily overdeveloped. The water level in most of the 

wells is still considerably above the top of the Dakota Sandstone and, 

with the present rate of development, a rapid decline would not be 

expected. Because it is deeper than the Dakota Sandstone, the
P8 CONTRIBUTIONS TO THE HYDROLOGY OP THE UNITED STATES

R. 68 W. R. 57 W.

Base modified from maps prepared 

by the Army Map Service

Well

feet, lo the piezometfic surface. F indicates o flowing 

we//

Hydrology by William G. Weist, Jr., 1960. 

Geology from geologic map of Colorado 

(U.S. Geological Survey)

EXPLANATION

Approximate areas 

of outcrop of the 

Dakota Sandstone 

and the Purgatoire 

Formation

CONTOUR INTERVAL 100 FEET

Approximate areas 

where the Dakota 

Sandstone and the 

Purgatoire Formation have been 

eroded away

10 MILES 

I

FIGURE 3. Map of report area showing approximate depth to plezometric surface 

of water in the Dakota Sandstone, 1959-60.
WATER IN DAKOTA AND PURGATOIRE FORMATIONS

109

115 ' 

1959 1960 1961

FIGURE 4.- -Fluctuations of the water level In a 510-foot well tapping the Dakota Sandstone south of La Junta, Colo.

Cheyenne Sandstone Member of the Purgatoire Formation is much 

less developed. Of the wells inventoried in the area, 27 are reported 

to tap only the Cheyenne Sandstone Member, 102 are reported to 

tap only the Dakota Sandstone, and 42 are reported to tap both 

sandstones.

RECHARGE AREAS

The aquifers are recharged mainly in their areas of outcrop to the 

south and west of Otero County. The water for recharge comes 

principally from direct precipitation, although some water percolates 

into the aquifers from streams that cross the outcrops.

Conditions are most favorable for recharge where the outcrop areas 

are flat-lying. The outcrops of the aquifers along the foot of the 

Front Range west of Otero County are very narrow owing to their 

steep dip to the east. Most of the precipitation on them rurs off the 

steep slope, and only a small amount recharges the aquifers. In outcrop areas east of the foothills, such as the plateaus along the Purga-
P10 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

toire River and the area northwest of Thatcher extending from the 

Apishapa River to the Huerfano River, the aquifers are r^arly flatlying. However, the deep canyons in the area along the Purgatoire 

River drain off some of the water that would otherwise recharge the 

aquifers. Some recharge also occurs in areas where the aquifers are 

overlain by unconsolidated upland deposits.

At this writing, no information is available on the amount of recharge received by the aquifers.

DEVELOPMENT AND UTILIZATION

HISTORY OF DEVELOPMENT

The earliest study of the geology and ground-water resources of this 

area was made by Gilbert (1896) who reported the existence of six 

artesian wells at Rocky Ford and La Junta, but did not record the 

year when the first well tapping the Dakota Sandstone war drilled in 

this area. In a footnote to page 584, Gilbert noted that the first two 

wells at La Junta that penetrated the Cheyenne Sandstorm Member 

of the Purgatoire Formation were drilled in 1896. It appears that 

these were the first wells in the area to penetrate this acmifer.

Several more wells were drilled in the area during tl*e next 10 

years. Darton (1906, p. 52-57, 62-63) reported "several" artesian 

wells at Rocky Ford and La Junta, at least four each at Timpas 

and Ayers, two each at Bloom and Cheraw (Holbrook), and one each 

at Sugar City, Ordway, Fowler, and Manzanola. By 190- the drop 

in artesian pressure at La Junta was great enough to require that 

most of the wells there be pumped. The towns of Ayers r.iid Bloom 

no longer exist.

The aquifers were developed slowly during the next few years. 

Pattoii (1923) in his study of the ground-water possibilities of the 

La Junta area, reported at least 50 artesian wells, including 10 that 

tapped only the Cheyenne Sandstone Member and 6 that tapped 

both aquifers. The greatest development took place between 1949 

and 1959, when at least 60 artesian wells were drilled as compared 

to 30 during the previous decade.

PRESENT UTILIZATION

The following table summarizes the use in 1960 of water from the 

Dakota Sandstone and the Cheyenne Sandstone MemHr of the 

Purgatoire Formation in the area:
WATER IN DAKOTA AND PURGATOIRE FORMATIONS Pll

Use

Stock and domestic (includes 

hauled water).

Total_-___-- _ _______

Wells

124

7 

17

10 

13

171

Source

/Pump _ _ 

\Flow __ _

Pump____ 

/Pump____ 

\Flow _ _

/Pump____ 

\Flow_ __

Range of 

yield (gpm)

4-60 

Trace-50 

4-85 

7-65 1-7 

10-75 

1. 5 

10

Approximate 

amount used 

(rnllions of 

gallons)

} 350 

45 

} 50

} 40 

0

485

STOCK AND DOMESTIC SUPPLIES

Of the artesian wells in Otero County and the southerr part of 

Crowley County, 120, or more than two-thirds, are privately owned 

stock and domestic wells. Of these, 79 are used solely for watering 

livestock, 32 are used for both livestock and domestic purposes, and

9 are used for domestic purposes only. Yields range generally from

10 to 25 gpm (gallons per minute), and some wells are reported to 

pump as much as 60 gpm. One well is reported to flow 50 gpm.

MUNICIPAL! SUPPLIES

Four towns in the area obtain all or part of their water supply 

from wells tapping one or both of the Cretaceous aquifers.

CJieraiv. The town of Cheraw uses an average of 12 mgy (million 

gallons per year) from a well tapping the Cheyenne Sandstone Member. The well, drilled in 1927 to a depth of 850 feet, is pumped at 65 

gpm. The water rises in the well to 60 feet below the land surface. 

In 1961, the town had a second well drilled. This well is 735 feet deep 

and yields a reported 85 gpm from the Dakota Sandstone.

Crowley. The town of Crowley uses more than 1 mgy from a well 

that is reported to tap the Cheyenne Sandstone Member of th*, Purgatoire Formation. The well was drilled to a depth of 1,432 feet and 

yields 4 gpm. The water rises in the well to 175 feet below the land 

surface. The town also has a supply of hard surface water for uses 

other than cooking and washing.

Manzanola. The town of Manzoiiola uses about 22 mgy from 2 

artesian wells. The older well was drilled in 1909 to a depth of 1,113 

feet penetrating 80 feet into the Dakota Sandstone. It is pumped 

at 50 gpm. The other well was drilled about 1924 to a depth of 1,365 

feet penetrating both aquifiers, and is pumped at 45 gpm. Both wells 

flowed until about 1944, but the pressure has declined and the water
P12 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

level is now about 80 feet below the land surface. Hard water from 

a well 37 feet deep is used for watering lawns.

Swink. The town of Swink uses about 10 mgy from two artesian 

wells. The older well, drilled in 1908 to a depth of 769 feet, taps 

both aquifers. The other well was drilled in 1920 to 555 feet and taps 

just the Dakota Sandstone. Both wells are pumped at 30 gpm. The 

water level in both wells has declined and now stands at about 65 feet 

below the land surface. Water for watering lawns is obtained from 

three shallow wells, each about 50 feet deep.

PRIVATE WATER ASSOCIATIONS

In 1954 a group of farmers near Cheraw organized the West Hoibrook Pipeline Co. They had a well drilled 886 feet through both 

artesian aquifers, and a pipeline was laid to distribute water to their 

farms for domestic and stock uses. Since then, at leapt 10 other 

water associations have been formed in Otero County and have either 

drilled new wells or utilized deep wells at abandoned schools. The 

10 associations in existence in 1959 used approximately 43 million 

gallons to serve more than 1,300 people.

Of the 17 wells presently in use by these organizations, 9 tap only 

the Dakota Sandstone. Yields are generally from 20 to 40 gpm, but 

one well yields only 10 gpm, 2 wells yield 50 gpm, and one well yields 

65 gpm.

WATER HAULING

In addition to distributing water through pipelines, several towns 

and water associations sell water to be hauled to other residences. 

Water hauled from Manzanola's wells serves nearly as m^ny people 

as the town's municipal system. A water hauler in Rocky Ford, who 

obtains water from five different wells, averages eight deliveries of 

1,000 gallons each day.

Some water haulers have their own wells. One in La Junta withdraws about 5 mgy from a well 700 feet deep tapping the Cheyenne 

Sandstone Member. The water rises to about 60 feet below the land 

surface and is pumped at 25 gpm. Others haul water from deep 

wells at schools in the area.

INDUSTRIAL, SUPPLIES

Ten artesian wells in the area are used for industrial purposes; they 

withdraw about 40 mgy from the two aquifers.

The processing plant of the Holbrook Turkey Growers Association 

in Cheraw uses about 6 mgy from a Dakota well 702 feet deep. In 

Rocky Ford, the Southern Colorado Power Co. has three wells that 

pump 40 to 50 gpm each from the two aquifers. The La Junta
WATER IN DAKOTA AND PURGATOIRE FORMATIONS P13

Kendering Co. uses about 22 mgy from a 624-foot well that taps both 

aquifers. The Best Laundry of La Junta uses more than 7 rogy from 

a 703-foot well.

CHEMICAL QUALITY OP WATER SAMPLES

The mineral content of a water determines its suitability for various 

uses. Water that is suitable for one use may not be suitable for 

another. The following discussion of water-quality criteria for various uses is taken largely from California Water Pollution Control 

Board (1952) and Hem (1959), and the reader is referred to these 

references for a more detailed discussion.

The quality of water considered suitable for domestic use varies 

widely from place to place. The following table presents some of the 

standards set by the U.S. Public Health Service (1946) for drinking 

water used in interstate commerce:

Iron and manganese combined should not exceed 0.3 ppm.

Magnesium should not exceed 125 ppm.

Sulf ate should not exceed 250 ppm.

Fluoride must not exceed 1.5 ppm.

Dissolved solids, recommended 500 ppm.

Dissolved solids, permissible 1,000 ppm.

Water containing minerals far in excess of the suggested concentrations is being used where better water is not available. People using 

such water become accustomed to it and apparently suffer no serious 

ill effects, except from water high in fluoride, which causes mottling 

of the teeth in young children.

Little has been written about quality of water desirable for livestock. Most animals seem to be able to tolerate water poorer in 

quality than that which can be used by humans. The upper limit of 

dissolved solids seems to range from 2,860 ppm for poultry to 12,900 

ppm for adult sheep (Hem, 1959, p. 241).

Water-quality requirements for industrial use vary greatly. For 

some uses, such as cooling or concentrating ores, almost any water 

can be used, whereas water of high quality is needed for makir g drugs, 

high-grade paper, and some other products. The report of the California State Water Pollution Control Board (1952) gives detailed 

information on industrial requirements.

Water from the Dakota Sandstone and the Cheyenne Sandstone 

Member of the Purgatoire Formation is generally soft and of the 

sodium sulfate type. In general, water in the two aquifers in the 

northern half of the area is much softer than that in the southern half. 

Locally, the water may be harder owing to local conditionr such as 

leakage from other formations through faulty casing or improper
P14 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

plugging of abandoned wells. Hardness of water samples collected 

from 23 wells tapping these two aquifers ranged from 8 to 906 ppm. 

This can be broken down as follows: less than 60 pprn (9 wells), 60 

to 120 ppm (2 wells), 120 to 180 ppm (1 well), more than 180 ppm 

(11 wells). Noncarbonate hardness constituted a major part of the 

hardness of the last 11 samples; it constituted more thar 50 percent 

of the hardness of the 8 samples having a hardness greater than 

400 ppm.

Water from these two aquifers is within the standard limits suggested by the U.S. Public Health Service (1946) for magnesium and 

chloride content, but commonly exceeds the standard limits for iron 

and manganese combined, sulfate, and fluoride. The following table 

summarizes the analyses (Weist, 1962).

Constituent

Silica_______ ______ _ _ __ _

Iron and manganese___ ____ _ ___ ____

Calcium __ __ _ _ _ __ _ _ __ _ __

Magnesium _. _____ _ _ _ ___

Sodium. _____ _____ __

Potassium ___ ___

Bicarbonate. __ ___

Sulfate ... . _ -_ _ _ __ ___ .

Chloride.. ______ __ _ ______

Fluoride__ _ __ ______ ____ _ ___

Total dissolved solids. _ _ _ __

Range 

(ppm)

6. 7-12

0-51

0-182

1. 2-110

116-670

2. 7-24

79-1, 030

211-1, 430

12-110

.4-3.2

750-2, 360

Suggested 

limit (ppm)

0. ?

125

250

250

1.5

1,000

Samples 

exceeding 

limit

14

0

22

0

8

17

Available chemical data are insufficient to differentiate between 

water from the Dakota Sandstone and water from the Cheyenne 

Sandstone Member of the Purgatoire Formation. Residents of the 

area report that the iron and hydrogen sulfide contents of water from 

the Cheyenne Sandstone Member generally are less thsn those of 

water from the Dakota Sandstone. Observations in the field indicate 

that this report may be true locally. Water in stock tanks filled 

from wells tapping the Cheyenne Sandstone Member is usually much 

clearer than water in tanks filled from wells tapping the Dakota 

Sandstone. Water from the Dakota is apt to be reddish brown and 

leaves a deposit in the stock tanks. This probably is due to local 

conditions within the formations because it is not found everywhere.

Darton (1906, p. 80-81) gives the results of analyse^ of water 

from 15 wells in this area. A comparison of the results of analyses 

done for this report with those reported by Darton shows no significant change in mineral content of the water. Figure 5 compares
WATER IN DAKOTA AND PURGATOIEB FORMATIONS P15

DATE OF ANALYSIS 

1960 1960 1895

EXPLANATION

Sodium and Potrssium

Magnesium

Calcium

Chloride, Fluoride, ard Nitrate

Sulfate

Bicarbonate (reported as 

carbonate in the 1895 

analysis)

Cheyenne Dakota Dakota 

Sandstone Sandstone Sandstone 

Member well in well in 

well in Swink, Rocky Ford, 

Cheraw, Colo Colo 

Colo

FIGURE 5. Analyses of ground water (in equivalents per million).
P16 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

analyses of water from the Cheyenne Sandstone Meml 3r and the 

Dakota Sandstone made in 1960 with an analysis made in 1895 of 

water from the Dakota Sandstone.

CONCLUSIONS

Supplies of comparatively soft water for domestic and stock use are 

available nearly everywhere in Otero County and in the southern part 

of Crowley County. These supplies are available from the Dakota 

Sandstone and the Cheyenne Sandstone Member of the Purgatoire 

Formation, which underlie nearly all of the area at depths ranging 

from 0 to 2,000 feet. In most places, supplies of water adequate for 

public supply and industrial use can be obtained. Water cannot 

always be obtained from these two aquifers in parts of the southeast 

corner of Otero County where the Purgatoire River and itr tributaries 

have cut through and partially drained the aquifers. The aquifers 

may be too deep in the northwestern part of the area to be economically 

feasible for developing water supplies at the present time.

Water in the aquifers is generally under artesian pressure and rises 

in the wells for a considerable distance above the top of the aquifer. 

In several places, water flows from the wells. In certain areas, such 

as around Cheraw and La Junta, the pressure on the water has declined because of the withdrawals by the large number of wells 

penetrating the aquifers.

Pumped wells yield from 4 to 75 gpm; some flowing wells yield as 

much as 50 gpm.

The chemical quality of the water is generally good except in some 

places where it has a rather high iron and sulfur content. There is 

no noticeable difference in mineral content or character of water from 

the two aquifers.

REFERENCES CITED

California State Water Pollution Control Board, 1952, Water-quality criteria:

California State Water Pollution Control Board Pub. 3., 512 p., 4 figs. 

Collins, W. D., Lamar, W. L., and Lohr, E. W., 1934, The industrial utility of

public water supplies in the United States, 1932: U.S. Geol. Srrvey WaterSupply Paper 658,135 p., 1 pi., 1 fig. 

Darton, N. H., 1906, Geology and underground waters of the Ark<msas Valley

in eastern Colorado: U.S. Geol. Survey Prof. Paper 52, 90 p., 28 pis. 

Gilbert, G. K., 1896, The underground water of the Arkansas Valley in eastern

Colorado: U.S. Geol. Survey 17th Ann. Rept, pt. 2, p. 551-601,13 pis., 5 figs. 

Hem. J. D. 1959, Study and interpretation of the chemical chare cteristics of

natural water: U.S. Geol. Survey Water-Supply Paper 1473, 2<>9 p., 2 pis.,

40 figs. 

Patton, H. B., 1923, Underground water possibilities for stock and domestic

purposes in the La Junta area, Colorado: Colo. Geol. Survey B-ll. 27, pt. 1,

p. 1-58, 2 pis., 4 figs. [1924].
WATER IN DAKOTA AND PURGATOIRE FORMATIONS P17

U.S. Public Health Service, 1946, Drinking water standards: Public Health 

Reports, v. 61, p. 11. [Repr. 2697.]

Weist, W. G., Jr., 1962, Records, logs, and water-level measurements o* selected 

wells, springs, and test holes, and chemical analyses of ground water in 

Otero and the southern part of Crowley Counties, Colorado: Co'o. Water 

Conserv. Board, Basic Data Rept. 11, Ground-Water Ser., 54 p., 1 pi., 1 fig.

U.S. GOVERNMENT PRINTING OFFICE:I9«J