U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5276

Prepared in cooperation with the National Park Service

Preliminary Hydrogeologic Assessment near Tassi and 

Pakoon Springs, Western Part of Grand Canyon-Parashant 

National Monument, Arizona
COVER 

Pakoon Springs, Grand Canyon-Parashant National Monument, Arizona. Photo by Margot Truini.
Prepared in cooperation with the National Park Service

Preliminary Hydrogeologic Assessment 

near Tassi and Pakoon Springs, Western 

Part of Grand Canyon-Parashant National 

Monument, Arizona

By Margot Truini

Scientific Investigations Report 2012–5276

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

Suggested citation:

Truini, M., 2013, Preliminary hydrogeologic assessment near Tassi and Pakoon Springs, western part of Grand 

Canyon-Parashant National Monument, Arizona: U.S. Geological Survey Scientific Investigations 

Report 2012–5276, 12 p.

Any use of trade, product, or firm 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.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Description of the Study Area ............................................................................................................2

Geologic Setting....................................................................................................................................2

Previous Investigations........................................................................................................................5

Acknowledgments................................................................................................................................5

Hydrogeology..................................................................................................................................................5

Geochemistry..................................................................................................................................................5

Summary..........................................................................................................................................................7

Future Studies.................................................................................................................................................7

References Cited..........................................................................................................................................11

Figures

1. Grand Canyon-Parashant National Monument, northwestern Arizona, showing location 

of the study area ...........................................................................................................................3

2. Map showing generalized geology in Grand Canyon-Parashant National Monument, 

northwestern Arizona ..................................................................................................................4

3. Water-level contours and general direction of groundwater movement, Grand CanyonParashant National Monument, northwestern Arizona.........................................................6

4. Grand Canyon-Parashant National Monument, northwestern Arizona, showing water 

chemistry and distribution of dissolved solids in the groundwater from springs..............9

5. Signatures of oxygen and hydrogen isotopes in water from selected springs in the Arizona 

Strip (A) and selected springs in Grand Canyon-Parashant National Monument, 

northwestern Arizona (B). Stable isotopic data are from the Grand Canyon 

Wildlands Council, Inc. (2002)...................................................................................................10

Tables

1. Water levels and aquifer geology for wells in the western part of Grand Canyon-Parashant 

National Monument, northwestern Arizona.............................................................................7

2. Major-ion and stable-isotope chemistry from springs in the western Grand Canyon-Parashant 

National Monument, northwestern Arizona.............................................................................8
iv

Conversion Factors

Inch/Pound to SI

Multiply By To obtain 

 Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

 Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

gallon (gal) 3.785 cubic decimeter (dm3

) 

 Flow rate

gallon per minute (gal/min) 0.06309 liter per second (L/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
Preliminary Hydrologic Assessment near Tassi and 

Pakoon Springs, Western Part of Grand Canyon-Parashant 

National Monument, Arizona

By Margot Truini

Abstract

Tassi and Pakoon Springs are both in the Grand Wash 

Trough in the western part of Grand Canyon-Parashant 

National Monument on the Arizona Strip. The monument is 

jointly managed by the National Park Service (NPS) and the 

Bureau of Land Management. This study was in response to 

NPS’s need to better understand the influence from regional 

increases in groundwater withdrawals near Grand CanyonParashant on the groundwater discharge from Tassi and 

Pakoon Springs. 

The climate of the Arizona Strip is generally semiarid to 

arid, and springs in the monument provide the water for the 

fragile ecosystems that are commonly separated by large areas 

of dry washes in canyons with pinyon and juniper. Available 

hydrogeologic data from previous investigations included 

water levels from the few existing wells, location information for springs, water chemistry from springs, and geologic 

maps. Available groundwater-elevation data from the wells 

and springs in the monument indicate that groundwater in the 

Grand Wash Trough is moving from north to south, discharging 

to springs and into the Colorado River. Groundwater may also 

be moving from east to west from Paleozoic rocks in the Grand 

Wash Cliffs into sedimentary deposits in the Grand Wash 

Trough. Finally, groundwater may be moving from the northwest in the Mesoproterozoic crystalline rocks of the Virgin 

Mountains into the northern part of the Grand Wash Trough. 

Water discharging from Tassi and Pakoon Springs has a 

major-ion chemistry similar to that of other springs in the western part of Grand Canyon-Parashant. Stable-isotopic signatures 

for oxygen-18 and hydrogen-2 are depleted in the water from 

both Tassi and Pakoon Springs in comparison to other springs 

on the Arizona Strip. Tassi Spring discharges from multiple 

seeps along the Wheeler Fault, and the depleted isotopic 

signatures suggest that water may be flowing from multiple 

places into Lake Mead and seems to have a higher elevation 

or an older climate source. Elevated water temperatures and a 

depleted stable-isotopic signature for Pakoon Springs suggest that the water may be traveling along a deep circulating 

flowpath, have multiple sources of water, been recharged at a 

high elevation, and (or) has an older climate source. 

Introduction

 Tassi and Pakoon Springs are both in the western part 

of Grand Canyon-Parashant National Monument, near the 

Arizona-Nevada State line on the Arizona Strip (fig. 1). The 

monument is jointly managed by the National Park Service 

(NPS) and the Bureau of Land Management (BLM). Tassi 

Spring, which is situated within the NPS parcel, and was 

developed as part of an original ranch homestead where the 

water from the spring was used for domestic and irrigation 

purposes. The cultural landscape and historic structures near 

Tassi Spring are currently being managed in part by Grand 

Canyon-Parashant National Monument and the Lake Mead 

National Recreation Area’s Cultural Resources Branch. Pakoon Springs, which was privately owned, was obtained by the 

BLM when the area became part of a national monument in 

November 2002 (Kathleen Harcksen, written commun., 2011). 

The NPS and BLM have been concerned for some time that 

increasing groundwater development near the communities of 

Mesquite, Nev., and St. George, Utah, could potentially affect 

the quantity and quality of groundwater discharging from 

Tassi and Pakoon Springs. To address this concern the NPS 

requested that the U.S. Geological Survey (USGS) conduct a 

technical evaluation of existing water-quality/chemical data, 

hydrologic data, and geologic maps to identify any gaps that 

would hinder defining the regional hydrogeology in relation to 

the flows at Tassi and Pakoon Springs. 

Tassi Spring is situated near an old ranch house on a 

bench where the water flows into an irrigation ditch, once 

delivered to pastures for cattle grazing but today moving 

through a breach in the levee where it enters Pigeon Wash 

downstream of the ranch house. Seeps below the main spring 

once serviced a cistern that was used to provide water to the 

house and corral, whereas other seep waters had been diverted 

away from the ranch buildings by a French drain system. Tassi 

Spring supports the rare endemic Grand Wash Spring snail, 
2 Preliminary Hydrologic Assessment near Tassi and Pakoon Springs, Western Part of Grand Canyon-Parashant National Monument

a candidate for Federal listing, and the riparian area provides 

habitat for a diverse bird population and a protective haven 

for local mammals in the Mojave Desert (Charles Drost, oral 

commun., 2010).

Pakoon Springs can potentially provide an oasis of high 

biologic diversity and productivity in the surrounding landscape 

of the arid desert. Pakoon Springs Ranch was a working ranch 

for nearly a century, including cattle ranching, alfalfa production, and ostrich farming. The springs were dug and developed 

into six manmade ponds to store water for domestic use and 

to irrigate agricultural fields. The springs, riparian areas, and 

agricultural fields had been overrun by nonnative, invasive floral 

and faunal species. From approximately 2002 to 2011, the BLM, 

with help from Grand Canyon Wildlands Council, Inc., and 

others, removed all the structures and restored the landscape to 

approximate conditions that likely existed before the establishment of the ranch (Kathleen Harcksen, oral commun., 2011).

Purpose and Scope

The purpose of this report is to provide an initial technical assessment of existing hydrologic, geologic, and geochemical data in the western part of Grand Canyon-Parashant 

National Monument in order to better understand the relation 

between the regional groundwater system and Tassi and Pakoon Springs. The assessment will determine gaps in the data 

needed to fully comprehend the effects of groundwater pumping by local communities on spring flows in Grand CanyonParashant National Monument. 

The scope of this study involved a preliminary analysis of 

existing spring discharge, groundwater level, water-chemical, 

and geologic data. This report examines existing hydrologic, 

geologic, and water-chemical data and provides a limited 

interpretation of the regional hydrogeology in relation to Tassi 

and Pakoon Springs as well as to other springs in the Grand 

Wash Trough in the western part of Grand Canyon-Parashant 

National Monument. Spring discharge and groundwater-level 

data were obtained from the USGS Groundwater Site Inventory (GWSI), water-chemical data were provided by the Grand 

Canyon Wildlands Council, Inc. (2002), and geologic data 

were gleaned from completed mapping projects (Bohannon 

and others, 1993; Billingsley and Workman, 2000; Billingsley 

and Wellmeyer, 2003; Billingsley and others, 2004; Felger and 

Beard, 2010; Langenheim and others, 2010). 

Description of the Study Area

Grand Canyon-Parashant National Monument, which was 

created by Executive order of President Clinton in 2000, is 

on the western side of the Arizona Strip (fig. 1). The monument is bounded on the west by the Arizona-Nevada State 

line, on the south-southwest by Grand Canyon National Park, 

on the northwest by the Virgin Mountains, and on the north 

and northeast by the Shivwits and Uinkaret Plateaus (fig. 1). 

The monument is more than 1 million acres in area, including 

parts of the Shivwits and Uinkerat Plateaus, the entire Grand 

Wash Drainage, the Toroweap Valley, and the Mount Trumbull 

and Mount Logan Wilderness Areas. The NPS manages most 

of the southern areas adjacent to the Grand Canyon, and the 

BLM manages the remaining areas to the north including the 

Mount Trumbull and Mount Logan Wilderness Areas (fig. 1). 

The Arizona Game and Fish Department manages wildlife 

within the study area, and a few private inholdings also exist 

within the monument, particularly at the town of Mount Trumbull in Potato Valley (fig. 1). 

Grand Canyon-Parashant National Monument is ecologically unique because the Sonoran, Great Basin, and Mojave 

Deserts all intersect in this region. The monument and the rest 

of the region provide critical habitat for several endangered 

or threatened species including the California condor, desert 

tortoise, willow flycatcher, bighorn sheep, endemic speckled 

dace, the Grand Wash Spring snail, pronghorn, and leopard 

frog. The fragile ecosystems supported by the springs are commonly separated by large areas consisting of dry washes in 

canyons with pinyon and juniper.

The climate of Grand Canyon-Parashant National 

Monument is generally semiarid to arid, with monthly 

averages for summertime and wintertime relatively close to 

climatologic data recorded at Pipe Spring National Monument (Western Regional Climate Center, http://www.wrcc.

dri.edu/cgi-bin/cliF302010.pl?az6616, accessed December 

10, 2012). Summertime average high temperatures at Pipe 

Spring National Monument range from 85 to 95 °F, and 

winter monthly average temperatures at range from 30 to 

40 °F. Total annual precipitation ranges from 5 inches (in) 

at the lowest elevations to 30 in at the highest elevations. 

Humidity is likewise extremely low in most environments 

but increases at higher elevations, and more than 90 percent 

of annual precipitation is estimated to be lost to evaporation 

and evapotranspiration (Iorns and others, 1965). 

Geologic Setting

Grand Canyon-Parashant National Monument straddles 

the Colorado Plateau to the east and the Grand Wash Trough 

of the Basin and Range Province to the west. Pakoon and Tassi 

Springs are both within the Grand Wash Trough of the Basin 

and Range Province (fig. 2). The boundary between the Colorado Plateau and the Basin and Range Province follows the base 

of the lower Grand Wash Cliffs along the approximate position 

of the Grand Wash Fault (Billingsley and others, 2004). 

The Grand Wash Trough is a 47 mile (mi) long depression, the north half of which comprises two major subbasins. 

The southern subbasin is a small 1- to1.5-mi deep half-graben 

that lies west of the Wheeler Fault; the northern subbasin, 

which is more than 2.5 mi deep, represents the deepest part of 

the Grand Wash Trough (fig. 2; Langenheim and others, 2010). 

The western margin of the Colorado Plateau consists of Paleozoic rocks that have been downfaulted and tilted westward 

toward the Grand Wash Trough. The west-dipping 
Introduction 3

Grand 

Wash 

Cliffs

Wilderness 

Paiute 

Wilderness 

Mt Logan 

Wilderness 

Mt Trumbull 

NEVADA 

ARIZONA 

Wilderness 

Colorado River

Land managed by BLM

BLM Wilderness Area 

State trust land

Privately owned land

Hualapai Reservation 

National monument boundary 

0 2.5 5 10 15

Miles

0 5 2.5 10 15

Kilometers 

National park/national recreation area

Uinkaret Plateau

Grand Wash Cliffs

Tassi Spring

Pakoon Springs

Hualapai Tribe 

Grand CanyonParashant NM 

Tucson

Phoenix 

Flagstaff

ARIZONA

Virgin Mountains

EXPLANATION

Pigeon Wash

Cottenwood Wash

Grand Wash drainage

Littlefield

BLAC KROCK ROA D

Wolf Hole

MountTrumbull

LAKE

MEAD

NATIONAL 

RECREATION 

AREA

GRAND

CANYON

NATIONAL

PARK

Hualapai Reservation 

15 KILOMETERS

15 MILES

0 2.5

0

5

2.5 5 10

10

LAKE

MEAD

NATIONAL 

RECREATION 

AREA

Shivwits Plateau

 M

TDELLENBAUGH ROAD

36°43’0”

36°13’0”

36°05’05”

MT TRUMBULL LOOP ROAD

Mesquite

Potato

Valley

Grand Wash Fault

Wheeler Fault

Grand

Wash

Trough

St. George, Utah

Figure 1. Grand Canyon-Parashant National Monument, northwestern Arizona, showing location of Tassi and Pakoon Springs.

For fault locations, see fig. 2. Modified from Bureau of Land Management (BLM), 2012.
4 Preliminary Hydrologic Assessment near Tassi and Pakoon Springs, Western Part of Grand Canyon-Parashant National Monument

Wheeler Ridge

Pakoon

Springs

Tassi

Spring

COLORADO

PLATEAU

Cenozoic surficial deposits and 

sedimentary rocks

Cenozoic volcanic and intrusive rocks

Mesozoic rocks

Paleozoic and Neoproterozoic rocks

Mesoproterozoic and Paleoproterozoic 

rocks

EXPLANATION

Fault—dashed where uncertain

Subbasin boundary

Northern Grand Wash Trough

BASIN 

AND

RANGE

PROVINCE

Southern subbasin 

estimated 1 to 1.5 miles

deep (Langenheim 

and others, 2011)

Northern subbsasin estimated

to be greater than 2.5 miles

deep (Langenheim and 

others, 2011)

113°30'0"

113°37'30"

36°30'0"

36°15'0"

36°7'30"

36°0'0" 

113°15'0"

114°0'0"

113°45'0"

36°45'0"

Base from U. S. Geological Survey

digital data, 1:100,000, 1982

Universal Transverse Mercator

Projection, Zone 12

0 10 20

0 15 30 KILOMETERS

MILES

Grand Wash Fault

Grand Wash Fault

Wheeler Fault

strata may represent large blocks of Paleozoic rocks that have 

been tilted along the Grand Wash Fault by footwall drag. Most 

of these tilted Paleozoic rocks have been buried by Cenozoic 

sedimentary and volcanic deposits. The major faults include 

the Grand Wash Fault, along which the Paleozoic strata of 

Wheeler Ridge were downdropped to the west and tilted eastward, and the Wheeler Fault, which truncates Wheeler Ridge 

and drops Paleozoic strata down to the west in the subsurface 

(Billingsley and others, 2004). 

Four Tertiary assemblages occupy the Grand Wash 

Trough and mostly bury the downdropped east-tilted fault 

blocks of Paleozoic and Mesozoic strata. (1) Earliest Cenozoic (24–18 Ma) sedimentary rocks consist of a lower redbrown conglomerate, a middle red siltstone and sandstone 

Figure 2. Generalized geologic map of Grand Canyon-Parashant National Monument, northwestern Arizona. Modified from Felger 

and Beard (2010).
Geochemistry 5

interbedded with gray silty limestone, and an upper limestone 

sequence (Bohannon, 1984). (2) The early Cenozoic sedimentary rocks are unconformably overlain by Tertiary rocks 

of the Grand Wash Trough and consist of fluvial and alluvial 

sedimentary deposits, freshwater-shallow-lake deposits, and 

shallow-basin evaporite deposits. (3) The deposits in the 

Grand Wash Trough are overlapped by the late Tertiary and 

Quaternary rocks of Grand Wash that crop out mostly west 

of the trace of the Wheeler Fault. These deposits consist of a 

basal conglomerate exposed along Grand Wash, overlain by 

red siltstone and sandstone of mostly fluvial and eolian origin. 

(4) Rocks of both the Grand Wash Trough and the Grand Wash 

are partly covered by extensive Pliocene basalt flows and 

interbedded fluvial gravel deposits between some of the flows. 

Early and late Tertiary alluvium and calcrete overlie the basalt 

flows (Billingsley and others, 2004). 

Tertiary basalt flows in the Grand Wash Trough are 

associated with fissure eruptions and pyroclastic vents in the 

upper reaches of Grand Wash Trough to the north of Pakoon 

Springs, with some dikes along Cottonwood Wash southeast 

of Pakoon Springs. Most of the basalt along Grand Wash 

originated from sources to the north of the Grand CanyonParashant National Monument boundary and flowed southward down ancestral Grand Wash and Cottonwood Wash 

toward the Colorado River during late Pliocene time (Billingsley and others, 2004). 

Tassi and Pakoon Springs, which are both to the west 

of the Grand Wash Fault within the Grand Wash Trough, 

discharge from the Cenozoic surficial deposits and sedimentary rocks that overlie the downfaulted east-dipping 

Paleozoic rocks. Pakoon Springs is to the east of the exposed 

east-dipping Paleozoic strata that form Pakoon Ridge, and 

Tassi Spring is on the west side of the exposed east-dipping 

Paleozoic strata along the Wheeler Fault (fig. 2; Billingsley 

and others, 2004). 

Previous Investigations

Levings and Farrar (1979) completed a groundwater 

study that included limited spring inventory data. The Grand 

Canyon Wildlands Council (2002) inventoried 100 springs on 

the Arizona Strip between 1999 and 2002, including an allinclusive survey of the fauna and water conditions at each site. 

 Multiple studies conducted within riparian areas along 

the upper Colorado River corridor have shown that the perennial and intermittent springs, seeps, and natural ponds support 

riparian habitats which house endangered, endemic, or other 

species of special concern (Clover and Jotter, 1944; Polhemus 

and Polhemus, 1987). 

Previous geologic maps provide descriptions of the geology and structure in the monument boundaries and surrounding area (Fisher, 1961; Bohannon and others, 1993; Beard, 

1996; Billingsley and Workman, 2000; Billingsley and others, 

2004; Billingsley and Wellmeyer, 2003; Felger and Beard, 

2010; Langenheim and others, 2010).

Acknowledgments

 I thank Gary Karst of the NPS and Kathleen Harcksen of 

BLM for their help and guidance in visiting Tassi and Pakoon 

Springs, for their assistance in developing an understanding 

of the landscape, and for their interest in guiding the preservation, restoration, and understanding of the hydrogeology of 

these springs. 

Hydrogeology

The hydrogeologic system that supports spring flow to 

Tassi and Pakoon Springs consists of complex lithologic and 

structural controls. The relation between groundwater discharge 

from Tassi and Pakoon Springs and groundwater movement 

within the Grand Wash Trough is poorly understood. Tassi 

Spring comprises several springs and seeps discharging along 

the west side of the Wheeler Fault alongside Pigeon Wash. 

Discharge from Tassi Spring was estimated to be 25 gallons per 

minute (gpm) in 1980. Pakoon Springs, which discharges from 

late Tertiary sedimentary rocks, is the largest spring in Grand 

Canyon-Parashant National Monument. Discharge from Pakoon 

Springs was estimated at 130 gpm in 1976.

Groundwater-level data for wells and springs measured 

in 1976 and 1997 that were retrieved from the USGS GWSI 

database (table 1) indicate that: (1) groundwater may be 

moving from north to south in the alluvium and sedimentary 

deposits within the Grand Wash Trough (fig. 3); (2) groundwater may be moving from east to west from Paleozoic 

rocks of the Grand Wash Cliffs into sedimentary rocks of the 

Grand Wash Trough (fig. 3); and (or) (3) groundwater may 

be moving from the northwest in Mesoproterozoic crystalline 

rocks of the Virgin Mountains into the northern part of the 

Grand Wash Trough. Regional groundwater recharge to the 

Grand Wash Trough may occur on the Grand Wash Cliffs and 

(or) the Virgin Mountains. Surface-water flows in washes in 

the Grand Wash Trough are ephemeral and occur only during 

larger runoff events. 

Geochemistry

A subset of water-chemical data obtained by the Grand 

Canyon Wildlands Council Inc. (2002) provides an initial 

characterization of the groundwater discharging from springs 

within the Grand Canyon-Parashant National Monument 

boundary (table 2). Water chemistry parameters that were 

analyzed included selected major ions (calcium, magnesium, 

sodium, chloride, sulfate, and bicarbonate) and stable isotopes 

of (oxygen-18 [18O] and deuterium [2H]). 

The variations in water chemistry and specific conductance measured from spring discharge (Grand Canyon 

Wildlands Council Inc., 2002) primarily reflect the rock types 

through which the water is moving (fig. 4). Tassi and Pakoon 

Springs are similar in water chemistry to many other springs in 
6 Preliminary Hydrologic Assessment near Tassi and Pakoon Springs, Western Part of Grand Canyon-Parashant National Monument

4500

4000

3500

3500

3000

2500

2000

1500

1000

5000

5500

2122

Spring—number is elevation, in feet above sea level

Well—number is water level, in feet above sea level

Water-level contour, in feet above sea level

(Dashed where uncertain)

EXPLANATION

COLORADO 

PLATEAU

Virgin Mountains

Grand Wash Trough

1

(Number in the center of the well correlates 

 to the well number in table 1)

113°30'0" 

113°37'30" 

 36°30'0"

36°15'0"N

36°7'30"

36°0'0" 

113°15'0" 

114°0'0"

113°45'0"

36°45'0"

Base from U.S. Geological Survey

digital data, 1:100,000, 1982

Universal Transverse Mercator

Projection, Zone 12

0 10 20

0 15 30 KILOMETERS

MILES

2122

3491

3556

2230

2231

1995

1918

4380

4120

4320

4220

5180

5500

3580 1180

1310

2240

420

1610

1720

1560

5780

7310

6580

6470

6360 6870

5120

4797

5750

5760

5960

6040

1

2

3 4

5

7

6

Arrow indicates direction of groundwater flow 

Figure 3. Water-level contours, springs, and wells in Grand Canyon-Parashant National Monument, northwestern Arizona.
 Summary 7

Well number

(from fig. 3)

Station name

Elevation 

of land

surface 

 (feet) 

Water level, 

below land

 surface 

 (feet)

Water level, 

elevation 

above sea level

 (feet)

Date of measurement Aquifer geology

1 (B-38-15) 27CCA 759 3,491 10/29/1991 Unconsolidated sedimentary deposits

2 (B-37-15) 18DBC 3,562

4,250

6 3,556 10/15/1997 Unconsolidated sedimentary deposits

3 (B-36-15) 28BDD 2,880 650 2,230 9/22/1976 Unconsolidated sedimentary deposits

4 (B-36-15) 25DCD 2,739 508 2,231 1/15/1997 Basalt

5 (B-35-16) 36DAD 2,000 5 1,995 9/22/1976 Unconsolidated sedimentary deposits

6 (B-35-15) 22BAD 2,340 218 2,122 9/21/1976 Basalt

7 (B-34-15) 05DAB 2,044 126 1,918 9/21/1976 Basalt

the western part of Grand Canyon-Parashant National Monument, characterized by low dissolved solids (< 500 milligrams 

per liter (mg/L); fig. 4). However, both Spring 106 and Cove 

Springs in the western part of the monument have a high content of total dissolved solids (>2,500 mg/L) with elevated concentrations of sulfate (SO4

2-) and calcium (Ca2+), suggesting the 

presence of gypsum (CaSO4

.

2H2O) and (or) anhydrite (CaSO4) 

along the groundwater flowpath. The water from Burro Spring 

has the highest content of total dissolved solids in the study 

area (6,677 mg/L), with elevated concentrations of sodium 

(Na+), chloride (Cl−), and SO4

2-, suggesting the presence of 

halite (NaCl). The chemistry of Burro Spring differs significantly from that of Tassi, Buckhorn, and Whiskey Springs, all 

of which are relatively close to Burro Spring (fig. 4).

Stable-isotopic data (Grand Canyon Wildlands Council 

Inc., 2002) indicate that Tassi and Pakoon Springs have a more 

depleted isotopic signature relative to that of other springs on 

the Arizona Strip, including those in Grand Canyon-Parashant 

National Monument (fig. 5A). Isotopic signatures for springs 

in the monument generally indicate that springs located in the 

western part of the monument may have different recharge 

regimes from those in the eastern part (fig. 5B; table 2). 

Tassi and Pakoon Springs have a more depleted stableisotopic signature and elevated temperture relative to other 

springs in Grand Canyon-Parashant National Monument. 

Several environmental conditions that could result in these 

signatures include (1) deep-circulating groundwater flowpaths; (2) a mixture of older and younger groundwater, 

suggesting multiple recharge sources and groundwater 

flowpaths; (3) seasonal variations from winter and summer 

storms; and (or) (4) a higher recharge elevation. Tassi Spring 

discharges from multiple seeps along the Wheeler Fault, and 

its depleted isotopic signature suggests that water may be 

flowing from multiple places into Lake Mead that seem to 

have a higher elevation or an older climate source. Elevated 

water temperatures and a depleted stable-isotopic signature 

for Pakoon Springs suggest that the water may be traveling 

along a deep-circulating flowpath, have multiple sources, 

has been recharged at a high elevation, and (or) has an older 

climate source. 

Summary 

Available hydrologic and water-chemical data are 

sparse for the western part Grand Canyon-Parashant 

National Monument near Tassi and Pakoon Springs in 

the Grand Wash Trough. Groundwater movement in and 

recharge to the Grand Wash Trough is poorly understood. 

Existing groundwater-level data indicate that groundwater may be moving from north to south in the Grand 

Wash Trough and receiving recharge from the Grand 

Wash Cliffs and the Virgin Mountains to the east and 

northwest, respectively. Water-chemical data indicate 

that many of the springs, including Tassi and Pakoon 

Springs, have a low content of total dissolved solids, and 

only a few springs have higher content of total dissolved 

solids. Tassi and Pakoon Springs have depleted 18O and 2

H stable-isotopic signatures relative to springs on the 

Arizona Strip or within the monument. Stable-isotopic 

signatures for Tassi and Pakoon Springs may result from 

(1) deep-circulating groundwater flowpaths; (2) a mixture 

of older and younger groundwater suggesting multiple 

recharge sources and groundwater flow paths; (3) seasonal 

variations from winter and summer storms; and (or) (4) a 

higher recharge elevation.

Future Studies

Previous studies did not focus on constructing a 

conceptual hydrogeologic-framework model to better 

understand the relation of the geologic structure, lithology, and groundwater movement between Grand CanyonParashant National Monument and the towns of Mesquite, 

Nev., and St. George, Utah. Historical water-level data 

from the few existing wells in the monument provided 

Table 1. Water levels and aquifer geology in wells in the western part of Grand Caynon-Parashant National Mounment, 

northwestern Arizona. 

[Data from U.S. Geological Survey Groundwater Site Inventory]
Table 2. Major-ion and stable-isotope chemistry from springs in the western part of Grand Canyon-Parashant National Monument, northwestern Ariz[All data collected by the Grand Caynon Wildlands Council Inc. (2002); mg/L, milligram per liter; per mil, parts per thousand; --, no data; latitude and longitude in degrees-minu

Site Latitude Longitude Calcium Magnesium Sodium Potassium Chloride Sulfate Bicarbonate Alkalinity, as CaCO 3 Dissolved solids De

mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L 

Buckhorn Spring 361909 1135828 77.0 37.0 20.7 7.1 91 106 255 209 464 

Burro Spring 361700 1140015 399 130 1655 10.5 2,254 2,147 166 136 6,677 

Cane Spring 363912 1134709 36.3 10.0 7.2 1.5 3 10 168 138 151 

Cove Spring 363259 1140000 386.0 164.0 143.0 1.6 158 1,618 180 148 2,559 

Hidden Spring 362812 1133744 58.2 19.9 9.3 1.3 28 67 169 139 267 

Lower Pigeon Spring 361800 1134115 44.1 33.7 13.2 2.3 49 12 246 202 276 

Middle Spring 363207 1140245 43.4 35.3 4.5 0.7 5 9 291 239 241 

Mud Spring 364146 1134649 43.9 16.1 17.5 1.7 24 19 166 136 203 

Pakoon Springs 362458 1135726 99.2 19.0 18.0 13.0 57 50 185 152 348 

Rattlesnake Spring 362753 1134039 54.1 14.2 13.8 0.8 19 28 194 159 224 

Red Rock Spring 363304 1140129 87.2 34.0 20.0 1.7 25 6 421 345 380 

Spring 106 364120 1134444 492.0 268.0 217.0 6.1 182 2,315 230 189 3,592 

Tassi Spring 361524 1135729 45.7 28.0 25.2 2.6 27 84 169 139 296 

Upper Jump north 363552 1134437 84.8 26.0 8.0 0.8 18 221 146 120 431 

Upper Jump south 363546 1134443 62.8 22.4 7.2 0.9 13 111 154 126 293 

Upper Pigeon Spring 361733 1133951 52.3 25.0 25.7 1.2 98 17 243 199 339 

Lower Pigeon Spring 361730 1133951 23.0 28.3 25.7 0.6 89.8 21.5 172 141 273 

Whiskey Spring 361848 1135852 50.6 26.5 17.0 2.1 8 88 190 156 286 
 Summary 9

 80 64 48 32 16 16 32 48 64 80 (meq/l)

Sodium and potassium Chloride and fluoride

Calcium Bicarbonate and carbonate

Magnesium Sulfate

WATER-CHEMISTRY DIAGRAM - Shows major

 chemical constituents in Millequivalence per

 liter. The diagrams are a variety of shapes and 

 sizes and provide a means of comapring,

 corrolating, and characterizing types of water. 

 Number, 6677, is dissolved-solids concentration,

 in milligrams per liter

6677

Cenozoic surficial deposits and 

sedimentary rocks

Cenozoic volcanic and intrusive rocks

Mesozoic rocks

Paleozoic and Neoproterozoic rocks

Mesoproterozoic and Paleoproterozoic rocks

Spring used for collection of water-quality data

0 10 20

0 15 30 KILOMETERS

MILES

EXPLANATION

Buckhorn Spring

Whiskey Spring

Middle Spring

Red Rock Spring

Pakoon Springs

Mud Spring

Cane Spring south

Upper Jump north

Upper Jump south

Spring 106

Upper Pigeon Spring

Lower Pigeon Spring

Rattlesnake Spring

Hidden Spring

Tassi Spring

Burro Spring

Cove Spring

276

464

6677

151

2559

267

203

348

224

380

3592

296

431

293

339

273

286

241

Virgin Mountains

Northern Grand Wash Trough

COLORADO

PLATEAU

113°30'0" 

113°37'30" 

 36°30'0"

 36°15'0"

36°7'30"

36°0'0"

113°15'0" 

 114°0'0"

113°45'0"

36°45'0"

Base From U.S. Geological Survey

digital data, 1:100,000, 1982

Universal Transverse Mercator

Projection, Zone 12

Figure 4. Grand Canyon-Parashant National Monument, northwestern Arizona, showing water chemistry and distribution of 

dissolved solids in the groundwater from springs. Data from the Grand Canyon Wildland Council, Inc. (2002).
10 Preliminary Hydrologic Assessment near Tassi and Pakoon Springs, Western Part of Grand Canyon-Parashant National Monument

-140.0

-120.0

-100.0

-80.0

-60.0

-40.0

-20.0

0.0

-18.00 -16.00 -14.00 -12.00 -10.00 -8.00 -6.00 -4.00 -2.0 0

West Grand Canyon-Parashant Springs

Tassi and Pakoon Springs

East Grand Canyon-Parashant Springs

Tassi Spring

Pakoon Springs

GLOBAL MEAN METEORIC-WATER LINE

0.0

A

B

-140.0

-120.0

-100.0

-80.0

-60.0

-40.0

-20.0

0.0

-20.00 -15.00 -10.00 -

 

 

 

Arizona Strip Springs

5.0 0.0 10.0 15.0 20.0

Tassi and Pakoon Springs GLOBAL MEAN METEORIC-WATER LINE

δ O, 

Pakoon Springs

Tassi Spring

δ O, 

δ

H, δ

H, in per mil in per mil

in per mil

in per mil

Figure 5. Signature of oxygen and hydrogen isotopes in water from selected springs in the Arizona Strip 

(A) and in Grand Canyon-Parashant National Monument, northwestern Arizona (B). Stable isotopic data 

are from the Grand Canyon Wildlands Council, Inc., (2002). Units are given in parts per thousand (per mil).
Summary 11

some indication of groundwater movement and direction 

but did not account for structural and lithologic controls. For 

example, does water move east to west from the Paleozoic 

rocks downward into the Grand Wash Trough, and what are 

the hydrogeologic units? How do the subbasins below the 

Grand Wash Trough (Langenheim and others, 2010) affect 

the movement of groundwater? Are the Virgin Mountains 

a barrier to groundwater movement between the towns of 

Mesquite, Nev., St. George, Utah, and the monument? The 

existing water-chemistry data were collected (Grand Canyon 

Wildlands Council Inc., 2002) with a primary focus on each 

individual spring and do not provide information about the 

regional connectedness of the springs to the local groundwater systems and hydrogeologic units. What are the groundwater flowpaths, and how old is the water discharging from 

the springs? Is there a mixture of old and young groundwater, suggesting local and nonlocal recharge? Where are the 

recharge sites for the regional groundwater system? What 

is the hydrologic connection between Tassi and Pakoon 

Springs and (or) other springs and the regional groundwater 

system? How old is the water from wells developed in Mesquite, Nev., and St. George, Utah, and does it have a similar 

recharge signature to water in the monument?

Answers to these questions can be addressed through 

studies that include remeasuring water levels from existing 

wells to compare the water levels measured in the late 1960s 

to mid-1970s and in the late 1990s, which could be used to 

discern any changes in the elevation of the groundwater table. 

Water-level measurements from wells developed in Mesquite, 

Nev., and St. George, Utah, would provide additional information about groundwater movement and direction in relation to 

the faults and fractures through the Mesoproterozoic crystalline rocks of the Virgin Mountains. 

Additional water-chemical sampling from Tassi and 

Pakoon Springs and selected springs and wells will include (1) 

resampling for major and minor ions and for stable isotopes 

(

18O and 2

H) to reduce the uncertainty in seasonal variations and 

the variation due to discharge points; (2) analysis of 14C to date 

the older groundwater component; (3) analyses of chlorofluorocarbons (CFCs), noble gases, sulfur hexafluoride (SF6

), and 

tritium (3H) to date the modern component of the groundwater; 

(4) analysis of groundwater and rocks for strontium-87 (87Sr), to 

provide geochemical signatures in order to discern groundwater 

flowpaths and identify the hydrogeologic units; (5) analysis 

for noble gases from selected springs and wells within Grand 

Canyon-Parashant National Monument and the cities of Mesquite, Nev., and St. George, Utah, to define recharge elevations; 

and (6) deployment of three to four sets of rain buckets from 

upper elevations down to lower elevations to collect rainwater 

in order to measure 18O and 2H to determine the most likely 

source elevation from the spring water.

Geophysical tools can be used to measure the resistivity 

of the rocks in order to characterize the structure and subsurface lithology, and to better understand local structural and 

lithologic controls near Tassi and Pakoon Springs. Geophysical tools can also be used to understand the subsurface 

structure and lithology of the rocks in areas where no other 

subsurface data exist. 
12 Preliminary Hydrologic Assessment near Tassi and Pakoon Springs, Western Part of Grand Canyon-Parashant National Monument

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References Cited 13

Menlo Park Publishing Service Center, California

Manuscript approved for publication November 9, 2012

Edited by George Havach and Claire Landowski

Layout and design by Judy Weathers
Truini—Preliminary Hydrogeologic Assessment near Tassi and Pakoon Springs, Western Part of Grand Canyon-Parashant National

Monument, Arizona—Scientific Investigations Report 2012–5276