Water-Quality Data Analysis of the 

Upper Gunnison River Watershed, 

Colorado, 1989–99

By Jason J. Gurdak, Adrienne I. Greve, and Norman E. Spahr

Denver, Colorado

2002

Prepared in cooperation with the

CITY OF GUNNISON

COLORADO RIVER WATER CONSERVATION DISTRICT

CRESTED BUTTE SOUTH METROPOLITAN DISTRICT

GUNNISON COUNTY

MOUNT CRESTED BUTTE WATER AND SANITATION DISTRICT

NATIONAL PARK SERVICE

TOWN OF CRESTED BUTTE

UPPER GUNNISON RIVER WATER CONSERVANCY DISTRICT

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02–4001
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

U.S. Geological Survey

Information Services

Box 25286

Denver Federal Center

Denver, CO 80225

from:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046
FOREWORD

The U.S. Geological Survey (USGS) is committed 

to serve the Nation with accurate and timely scientific 

information that helps enhance and protect the overall 

quality of life, and facilitates effective management 

of water, biological, energy, and mineral resources. 

(http://www.usgs.gov/). Information on the quality 

of the Nation’s water resources is of critical interest to 

the USGS because it is so integrally linked to the longterm availability of water that is clean and safe for 

drinking and recreation and that is suitable for industry, irrigation, and habitat for fish and wildlife. Escalating population growth and increasing demands for 

the multiple water uses make water availability, now 

measured in terms of quantity and quality, even more 

critical to the long-term sustainability of our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. (http://water.usgs.gov/nawqa). Shaped by 

and coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is 

designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the 

conditions changing over time? How do natural features and human activities affect the quality of streams 

and ground water, and where are those effects most 

pronounced? By combining information on water 

chemistry, physical characteristics, stream habitat, and 

aquatic life, the NAWQA Program aims to provide 

science-based insights for current and emerging water 

issues and priorities. NAWQA results can contribute to 

informed decisions that result in practical and effective 

water-resource management and strategies that protect 

and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 50 

of the Nation’s most important river basins and aquifers, referred to as Study Units. (http://water.usgs.gov/

nawqa/nawqamap.html). Collectively, these Study 

Units account for more than 60 percent of the overall 

water use and population served by public water 

supply, and are representative of the Nation’s major 

hydrologic landscapes, priority ecological resources, 

and agricultural, urban, and natural sources of 

contamination.

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments thereby build local knowledge 

about water-quality issues and trends in a particular 

stream or aquifer while providing an understanding 

of how and why water quality varies regionally and 

nationally. The consistent, multi-scale approach helps 

to determine if certain types of water-quality issues are 

isolated or pervasive, and allows direct comparisons of 

how human activities and natural processes affect 

water quality and ecological health in the Nation’s 

diverse geographic and environmental settings. Comprehensive assessments on pesticides, nutrients, volatile organic compounds, trace metals, and aquatic 

ecology are developed at the national scale through 

comparative analysis of the Study-Unit findings. 

(http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and relevant 

science so that the most recent and available knowledge about water resources can be applied in management and policy decisions. We hope this NAWQA 

publication will provide you the needed insights and 

information to meet your needs, and thereby foster 

increased awareness and involvement in the protection 

and restoration of our Nation’s waters. 

The NAWQA Program recognizes that a national 

assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for a fully integrated 

understanding of watersheds and for cost-effective 

management, regulation, and conservation of our 

Nation’s water resources. The Program, therefore, 

depends extensively on the advice, cooperation, and 

information from other Federal, State, interstate, 

Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder 

groups. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch

Associate Director for Water

FOREWORD III
CONTENTS V

CONTENTS

Foreword ................................................................................................................................................................................ III

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

Introduction............................................................................................................................................................................ 2

Purpose and Scope....................................................................................................................................................... 4

Acknowledgments ....................................................................................................................................................... 4

Study Area ............................................................................................................................................................................. 4

Hydrology .................................................................................................................................................................... 6

Geology........................................................................................................................................................................ 6

Methods of Data Analysis ..................................................................................................................................................... 8

Data Sources ................................................................................................................................................................ 10

Data Quality Assurance ............................................................................................................................................... 10

Data Compilation and Comparison ............................................................................................................................. 10

Temporal Trend Analysis............................................................................................................................................. 11

Surface-Water Quality ........................................................................................................................................................... 12

Field Properties............................................................................................................................................................ 12

Major Ions.................................................................................................................................................................... 15

Nutrients ...................................................................................................................................................................... 17

Spatial Distribution and Comparison to State Standards................................................................................... 18

Temporal Trends ................................................................................................................................................ 18

Land-Use Comparison....................................................................................................................................... 22

Trace Elements............................................................................................................................................................. 24

Spatial Distribution and Comparison to State Standards................................................................................... 24

Temporal Trends ................................................................................................................................................ 28

Streambed Sediment .......................................................................................................................................... 28

Suspended Sediment.................................................................................................................................................... 28

Biology and Other Characteristics............................................................................................................................... 30

Chlorophyll-a..................................................................................................................................................... 30

Blue Mesa Reservoir Chlorophyll-a ........................................................................................................ 30

Stream Chlorophyll-a .............................................................................................................................. 35

Biochemical Oxygen Demand........................................................................................................................... 35

Fecal Coliform................................................................................................................................................... 35

Ground-Water Quality ........................................................................................................................................................... 39

Field Properties............................................................................................................................................................ 41

Major Ions and Dissolved Solids ................................................................................................................................. 41

Nutrients ...................................................................................................................................................................... 44

Trace Elements and Radon .......................................................................................................................................... 45

Pesticides and Volatile Organic Compounds ............................................................................................................... 46

Summary................................................................................................................................................................................ 46

References.............................................................................................................................................................................. 48

Appendix A—Selected surface-water sites in the upper Gunnison River Basin................................................................... 53

Appendix B—Characteristics of ground-water-quality sites in the upper Gunnison River watershed, 1970–99 ................. 59

FIGURES

1–8. Maps showing:

1. Location of the upper Gunnison River watershed study area ......................................................................... 3

2. Land use in the upper Gunnison River watershed, 1990 ................................................................................ 5

3. Location of selected U.S. Geological Survey streamflow-gaging stations and mean monthly 

discharge (water year 1999) for selected stations ........................................................................................... 7

4. Geology of the upper Gunnison River watershed........................................................................................... 8

5. Spatial distribution of median specific conductance, October 1989 to December 1999 ................................ 16
VI CONTENTS

6. Spatial distribution of median ammonia concentrations, October 1989 to December 1999 .......................... 19

7. Spatial distribution of median nitrate concentrations, October 1989 to December 1999............................... 20

8. Spatial distribution of median total phosphorus concentrations, October 1989 to December 1999 .............. 21

9. Boxplots showing distribution of (A) ammonia, (B) nitrate, and (C) total phosphorus concentrations 

by land-use classification for surface water, October 1989 to December 1999 ...................................................... 23

10–13. Maps showing:

10. Spatial distribution of median cadmium concentrations, October 1989 to December 1999 .......................... 25

11. Spatial distribution of median silver concentrations, October 1989 to December 1999 ................................ 26

12. Spatial distribution of median zinc concentrations, October 1989 to December 1999 .................................. 27

13. Exceedances of Colorado Department of Public Health and Environment in-stream water-quality 

standards for dissolved trace elements, October 1989 to December 1999 ..................................................... 31

14. Graph showing flow-adjusted dissolved iron concentration at site 47 (Gunnison River at County 

Road 32), October 1995 to December 1999............................................................................................................ 32

15–20. Maps showing:

15. Spatial distribution of streambed-sediment samples, October 1995 to August 1999, and 

comparison of selected trace-element concentrations to the Canadian Sediment Quality 

Guidelines Probable Effect Level ................................................................................................................... 33

16. Spatial distribution of median suspended-sediment concentrations, October 1994 to 

December 1999............................................................................................................................................... 34

17. Spatial distribution of median chlorophyll-a concentrations, December 1996 to 

September 1998 .............................................................................................................................................. 36

18. Spatial distribution of median biochemical oxygen demand concentrations, 

July 1995 to October 1999.............................................................................................................................. 37

19. Spatial distribution of median fecal coliform concentrations, October 1989 to 

December 1999............................................................................................................................................... 38

20. Spatial distribution of wells according to aquifer type, 1970 to 1999............................................................ 40

21. Boxplot showing distribution of dissolved-solids concentrations by aquifer type for ground-water 

samples, 1970 to 1999............................................................................................................................................. 43

22. Boxplot showing distribution of nitrate concentrations by land-use classifications for ground-water 

samples, 1970 to 1999............................................................................................................................................. 45

TABLES

1. Land use for the upper Gunnison River watershed ................................................................................................. 6

2. Summary of the number of analyses, minimum, median, and maximum concentrations for 

surface-water-quality samples in the upper Gunnison River watershed ................................................................. 13

3. Seasonal Kendall trend-analysis results for dissolved oxygen and pH in the upper Gunnison 

River watershed....................................................................................................................................................... 15

4. Seasonal Kendall trend-analysis results for selected nutrient species in the upper Gunnison 

River watershed....................................................................................................................................................... 22

5. Exceedances of Colorado Department of Public Health and Environment in-stream water-quality 

standards for dissolved trace elements in the upper Gunnison River watershed, October 1989 to 

December 1999 ....................................................................................................................................................... 29

6. Seasonal Kendall trend-analysis results for selected dissolved trace elements in the upper 

Gunnison River watershed ...................................................................................................................................... 32

7. Sites and number of samples with fecal coliform concentrations greater than 200 counts per 

100 milliliters in the upper Gunnison River watershed, October 1989 to December 1999 .................................... 39

8. Summary of the number of analyses, minimum, median, and maximum concentrations for 

ground-water-quality samples in the upper Gunnison River watershed ................................................................. 42

9. Description of dominant water types of sampled wells in the upper Gunnison River watershed........................... 44
CONTENTS VII

CONVERSION FACTORS AND ABBREVIATIONS

Degrees Fahrenheit (oF) may be converted to degrees Celsius (oC) by using the following equation: o

C = 5/9 (oF – 32).

Degrees Celsius (o

C) may be converted to degrees Fahrenheit (oF) by using the following equation: oF = 9/5 (oC) + 32.

Additional Abbreviations or Terms

BOD, Biochemical Oxygen Demand

CDPHE, Colorado Department of Public Health and Environment

ft, feet

LOWESS, Locally Weighted Scatterplot Smoothing

L, liter

MCL, Maximum Contaminant Level

mg/L, milligrams per liter

mi2

, square mile

mL, milliliter

mg/m2, milligrams per square meter

NPS, National Park Service

NTU, nephelometric turbidity unit

NWIS, U.S. Geological Survey National Water Information System

PEL, Probable Effect Level

pCi/L, picocuries per liter

s, second

STORET, U.S. Environmental Protection Agency Storage and Retrieval database

SDWR, Secondary Drinking Water Regulation

TVS, Table Value Standard

USEPA, U.S. Environmental Protection Agency

USFS, U.S. Forest Service

USGS, U.S. Geological Survey

VOC, Volatile Organic Compound

μg/L, micrograms per liter

μS/cm, microsiemens per centimeter at 25 degrees Celsius

WY, water year (October 1 to September 30) [WY 1980 = October 1, 1979, to September 30, 1980]

>, greater than

≅ , approximately equal to

Multiply By To obtain

acre 0.4049 hectare

acre-foot (acre-ft) 1,233 cubic meter

cubic foot (ft3) 0.02832 cubic meter

cubic foot per second (ft3

/s) 0.02832 cubic meter per second 

cubic foot per second (ft3/s) 28.32 liter per second

foot (ft) 0.3048 meter

foot per second (ft/s) 0.3048 meter per second

pound (lb) 0.4536 kilogram

square mile (mi2

) 2.59 square kilometer 
Abstract 1

Water-Quality Data Analysis of the Upper Gunnison 

River Watershed, Colorado, 1989–99

By Jason J. Gurdak, Adrienne I. Greve, and Norman E. Spahr

Abstract

Water-quality data from October 1969 

to December 1999 for both surface water and 

ground water in the upper Gunnison River 

watershed were retrieved and compiled from 

the U.S. Geological Survey National Water 

Information System and the U.S. Environmental 

Protection Agency Storage and Retrieval databases. Analyses focused primarily on a subset of 

these data from October 1989 to December 1999. 

The upper Gunnison River watershed is located 

west of the Continental Divide in the Southern 

Rocky Mountains physiographic province.

Surface-water-quality data were compiled 

for 482 sites in the upper Gunnison River watershed. Most values of surface-water temperature, 

dissolved oxygen, and pH were within Colorado 

Department of Public Health and Environment 

(CDPHE) in-stream standards. Calcium bicarbonate type water was the most spatially dominant water type in the basin. 

Nutrients were most commonly sampled 

along the Slate River and East River near Crested 

Butte and along the Gunnison River from the 

confluence of the East and Taylor Rivers to the 

western edge of the watershed. Median ammonia 

concentrations were low, with many concentrations less than laboratory reporting levels. All 

nitrate concentrations met the CDPHE in-stream 

standard of 10 milligrams per liter. More than 

30 percent of stream sites with total phosphorus 

data (23 of 61 sites) had concentrations greater 

than the U.S. Environmental Protection Agency 

(USEPA) recommendation for controlling 

eutrophication.

Ammonia concentrations at a site on 

the Slate River near Crested Butte had a statistically significant upward trend for the 1995–99 

period. The Slate River near Crested Butte site is 

located immediately downstream from the towns 

of Crested Butte and Mount Crested Butte and 

may reflect recent population growth or other 

land-use changes. However, the rate of change 

of the trend is small (0.017 milligram per liter 

per year). 

Although a multiple comparison test 

showed nitrate concentrations were statistically 

different between agriculture and forest sites and 

between agriculture and urban land-use classified 

sites, median concentrations were low among all 

land-use settings. Median concentrations of total 

phosphorus were greatest in rangeland areas and 

least in urban areas. No significant differences 

were identified for median concentrations of total 

phosphorus in agriculture and forest land-use 

areas.

Median concentrations of arsenic, lead, 

mercury, selenium, and silver were low or 

below reporting levels throughout the watershed. 

Aluminum, cadmium, copper, lead, manganese, 

and zinc concentrations were elevated near the 

town of Crested Butte and on Henson Creek 

upstream from Lake City, which may be 

explained by upstream areas of historical mining. 

Samples for six trace elements exceeded standards: cadmium, copper, lead, manganese, silver, 

and zinc. A downward trend (3 micrograms per 

liter per year) was identified for the dissolved iron 

concentration at a site on the Gunnison River at 

County Road 32 downstream from the city of 
2 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Gunnison. Streambed-sediment samples from 

areas affected by historical mining also had 

elevated concentrations of some trace elements.

Chlorophyll-a concentrations in samples 

from Blue Mesa Reservoir and streams in the 

Crested Butte and Gunnison areas were typical 

of unenriched to moderately enriched conditions. 

Median concentrations of 5-day biochemical 

oxygen demand concentrations for sites between 

Crested Butte and Blue Mesa Reservoir were 

less than 2 milligrams per liter. Occasional high 

(greater than 200 counts per 100 milliliters) 

concentrations for fecal coliform were determined 

at selected sites within the study area. However, 

median concentrations were less than 100 counts 

per 100 milliliters except for the Squaw Creek and 

Cimarron River areas in the western part of the 

watershed.

Ground-water-quality data have been 

collected by the U.S. Geological Survey from 

99 wells. Many wells were completed in aquifers 

composed of Holocene-age valley fill and alluvium. Most field properties were within the 

USEPA Secondary Drinking Water Regulations 

(SDWR) range for treated drinking water, except 

for 2 (of 40) pH samples. Calcium bicarbonate 

was the predominant water type in nearly all aquifers except for the aquifers composed of volcanic 

rock, which had more sodium and sulfate mixed 

water types. Wells with sulfate concentrations 

exceeding the SDWR of 250 milligrams per 

liter were completed in aquifers composed of 

volcanic rock near Lake City. Dissolution and 

oxidation of sulfide minerals in these aquifers 

may explain the elevated sulfate concentrations 

in ground water at these locations. 

Nutrient concentrations in ground water 

were generally low, and median concentrations 

for ammonia, nitrite, and dissolved phosphorus 

were below reporting levels. All nitrate concentrations in the samples were below the USEPA 

drinking-water maximum contaminant level of 

10 mg/L. No statistical difference was found in 

nitrate concentrations among the four land-use 

classifications (agriculture, forest, rangeland, 

and urban).

Trace elements in ground water were 

generally below the USEPA SDWR. Three 

iron samples exceeded the USEPA SDWR of 

300 micrograms per liter at two wells located 

near the city of Gunnison and at a well south of 

the town of Powderhorn near the Cebolla River. 

Nine of 39 manganese samples exceeded the 

USEPA SDWR of 50 micrograms per liter 

and were collected from aquifers composed 

of Holocene-age valley fill and alluvium near 

Gunnison and Crested Butte and in one well 

near the Cebolla River. Radon gas is a natural 

radioactive decay product of uranium. All 

39 radon samples collected from ground water 

in the watershed exceeded the proposed USEPA 

drinking-water maximum contaminant level of 

300 picocuries per liter and ranged from 426 to 

3,830 picocuries per liter. 

INTRODUCTION

The upper Gunnison River, located in 

south-central Colorado (fig. 1), drains approximately 

3,965 mi2

. The East and Taylor Rivers drain an area 

west of the Continental Divide, converge upstream 

from the city of Gunnison, and form the Gunnison 

River, which flows into the Wayne N. Aspinall Unit 

of the Colorado River Storage Project (Blue Mesa, 

Morrow Point, and Crystal Reservoirs) and the 

Curecanti National Recreation Area. Currently (2001), 

the Curecanti National Recreation Area, along with 

the Crested Butte Mountain Resort, attracts a large 

number of recreational visitors to the upper Gunnison 

River watershed, which historically was dominated by 

ranching and mining.

Population growth and changes in land-use 

practices have the potential to affect both water 

quality and quantity in the upper Gunnison River 

watershed. In 1995, the U.S. Geological Survey 

(USGS), in cooperation with local sponsors—City 

of Gunnison, Colorado River Water Conservation 

District, Crested Butte South Metropolitan District, 

Gunnison County, Mount Crested Butte Water and 

Sanitation District, National Park Service, Town of 

Crested Butte, and Upper Gunnison River Water 

Conservancy District—established a water-qualitymonitoring program in the upper Gunnison River 

watershed to characterize current water-quality 

conditions and to assess the effects of increased 
INTRODUCTION 3

urban development and other land-use changes on 

water quality. In order to evaluate the outcome of the 

water-quality monitoring program initiated in 1995, 

identify spatial and temporal gaps within the available 

water-quality data, evaluate the needed focus of future 

water studies, and ultimately aid in making informed 

land-use decisions in the watershed, the local sponsors 

expressed a need for a compilation and analysis of 

existing water-quality data. In 1999, the USGS, in 

cooperation with the local sponsors, initiated a retrospective analysis of water quality in the upper 

Gunnison River watershed.

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Colorado

107o30'

Upper Gunnison River Watershed

39o

107o

Lake City

SAN JUAN MOUNTAINS

Ceboll a Creek

Gunnison

Tomich i Creek

Gunnison Rive r

Blue Mesa Reservoir

Morrow Point

Reservoir Cocheto pa Creek

Q uartz Creek

Cimarron

Rive r

GUNNISON

MONTROSE

SAGUACHE

HINSDALE

Wil lo

w

Cr eek

We st Elk Creek

COCHET OPA HILLS

Crested Butte

Pitkin

Taylor Park Reservoir

Mount Crested

Butte

SAWATCH RANGE

SAWATCH

RANGE

Taylor River

East River

Red

Mountain

106o30' ELK MOUNTAINS

Slate River

Whetstone

Mountain

Ohio Cree

WEST ELK MOUNTA

k

INS

Soap Creek

Curecanti Creek

38 Crystal Reservoir o30'

38o

Watershed boundary

County boundary

Mountain

City or Town

EXPLANATION

Figure 1. Location of the upper Gunnison River watershed study area. 
4 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Purpose and Scope

This report presents the results of the 

compilation and analysis of available water-quality 

data for the upper Gunnison River watershed. The 

retrospective water-quality analysis was limited to 

water-quality data in an electronic (computerized 

database) format and included only samples gathered 

from October 1969 to December 1999. These waterquality data were gathered and reported by the 

USGS, U.S. Environmental Protection Agency 

(USEPA), Colorado Department of Public Health 

and Environment (CDPHE), National Park Service 

(NPS), U.S. Forest Service (USFS), Colorado 

Department of Natural Resources, and the Bureau 

of Reclamation. 

For selected water-quality properties and 

constituents in the watershed, this report presents 

a data summary, spatial distribution evaluation, 

comparison to Federal and State standards, and 

analyzes relations between land-use practices and 

water quality. Where the length of record was sufficient, trend analysis was conducted to identify changes 

in water quality over time. To assess the effects of land 

use on water quality, sites were grouped according to 

current land-use practices adjacent to each site, and 

water-quality data were compared among land-use 

classification groups.

Acknowledgments

The authors thank Matt Malick (National 

Park Service), Nancy Bauch, Bob Boulger, and 

Paul von Guerard (all U.S. Geological Survey) 

for assistance with compilation of water-quality 

data. Acknowledgments also are extended to 

Tyler Martineau and Tony Ranalli for technical 

reviews, Carol Anderson and Mary Kidd for 

editorial reviews, Joy Monson for manuscript and 

layout, and Sharon Powers Clendening for graphic 

design. 

STUDY AREA

The upper Gunnison River watershed is located 

west of the Continental Divide in the southern Rocky 

Mountains of Colorado. The watershed is primarily 

within Gunnison County, with smaller sections located 

in Saguache, Hinsdale, and Montrose Counties. The 

headwaters are in the Elk and West Elk Mountains to 

the north and in the San Juan Mountains, Cochetopa 

Hills, and Sawatch Range to the south and east (fig. 1). 

Major tributaries in the upstream portion of the watershed are the Slate River, East River, Taylor River, 

Ohio Creek, Tomichi Creek, and Cochetopa Creek. 

Other tributaries (such as Cebolla Creek, Lake Fork 

Gunnison River, and the Cimarron River) drain into 

the reservoirs of the Wayne N. Aspinall Unit of the 

Colorado River Storage Project west of Gunnison. The 

Aspinall Unit reservoirs include Blue Mesa, Morrow 

Point, and Crystal and are in the Curecanti National 

Recreation Area. The maximum elevation and outlet 

elevation of the watershed are 14,265 and 6,526 ft, 

respectively. The watershed area-weighted average 

annual precipitation is 23 inches (Colorado Climate 

Center, 1984).

Forest and rangeland are the dominant land 

uses in the watershed (fig. 2). About 57 percent of 

the watershed is forested and about 32 percent is 

used as rangeland (table 1). Barren land or tundra 

is the next largest land-use category, comprising about 

7.79 percent. Urban and built-up lands comprise only 

6 mi2 (0.14 percent) of the watershed (Fegeas and 

others, 1983; refined by Hitt, 1995). 

Communities were first established in the upper 

Gunnison River watershed during the mid- to late 

1800’s as a result of the boom in silver mining. By the 

end of the 1800’s, the silver mining boom had ended, 

leaving only towns that had other industries on which 

to base their economies. Crested Butte and Gunnison 

were able to rely on ranching, industry brought by 

the railroad and coal mining, and beginning in 1911, 

Western State College in Gunnison (Vandenbusche, 

2000).

Today, there are many small towns and 

communities in the watershed, but only two areas 

have populations numbering in the thousands: the city 

of Gunnison (1999 population of 5,498) and the town 

of Crested Butte, including the surrounding upper East 

River valley (1999 population of 2,274) (Colorado 

Department of Local Affairs, 2000). Although the 

resident population is relatively small, the region 

attracts a large number of visitors. The largest tourist 

draws in the watershed are the Curecanti National 

Recreation Area and Crested Butte Mountain Resort, 

which together attract more than 1.5 million visitors 
STUDY AREA 5

Urban or built-up

Agriculture

Rangeland

Forest

Water or wetland

Barren land or tundra

Crested Butte

Gunnison

Lake City

Pitkin

38°30'

107°30'

39°

107°

106°30'

38°

EXPLANATION

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 2. Land use in the upper Gunnison River watershed, 1990.
6 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

yearly (National Park Service, 2000; Gunnison County 

Chamber of Commerce, 2000). Tourism is the largest 

industry in Gunnison County, followed by education 

(Western State College) and ranching (Gunnison 

County Chamber of Commerce, 2000). Between 

1990 and 1999, the population of Gunnison had a 

modest increase from 4,636 to 5,498 (18 percent 

increase); however, during the same period, the 

combined population of Crested Butte and Mount 

Crested Butte increased from 1,214 to 2,274 

(87 percent increase) (Colorado Department of Local 

Affairs, 2000). Recently, plans were announced to 

construct 163 new homes in Crested Butte (Colorado 

Department of Labor and Employment, 2000). 

Hydrology

The USGS has operated 21 streamflow-gaging 

stations within the upper Gunnison River watershed 

at some time during the period of October 1969 to 

December 1999 (fig. 3). Some gages were discontinued at the end of WY 1970 and, therefore, have 

only 1 year of data within the period of study. During 

WY 1999, 13 gages were in operation, covering the 

major drainages in the watershed. Typical of the 

southern Rocky Mountains, the annual discharge 

pattern is dominated by spring snowmelt (fig. 3). A 

substantial increase in discharge is common beginning 

in April, peaking in May or June, and decreasing in 

July and August (sites 103 and 45) (fig. 3). The 

remainder of the year has relatively constant flow. 

Exceptions to the snowmelt-dominated hydrograph, 

recorded downstream from the Taylor and Crystal 

Reservoirs (sites 97 and 50), reflect controlled releases 

from upstream reservoirs (fig. 3). 

Surface water that is not used consumptively 

in the watershed drains to the three reservoirs of the 

Aspinall Unit. The operation of the three reservoirs—

Blue Mesa, Morrow Point, and Crystal—is controlled 

by the Bureau of Reclamation, whereas recreation in 

the Curecanti National Recreation Area is controlled 

by the National Park Service. Together, the reservoirs 

have a storage capacity of 1,083,126 acre-ft (Bureau 

of Reclamation, 1999). Blue Mesa Reservoir is the 

largest and most upstream of the three reservoirs, 

followed in size and downstream location by Morrow 

Point and Crystal Reservoirs. Based on data from 

1979 to 1999, Blue Mesa Reservoir has a maximum 

storage capacity of 940,700 acre-ft, a surface area 

of 9,180 acres at full pool, and an average residence 

time of 202 days, whereas Morrow Point and Crystal 

Reservoirs, respectively, have maximum storage 

capacities of 117,190 and 25,236 acre-ft, surface areas 

of 817 and 301 acres at full pool, and average residence times of 36 and 4.5 days (capacity and surfacearea data from Bureau of Reclamation [1999]; residence times from Nancy Bauch, U.S. Geological 

Survey, and Matt Malick, National Park Service, 

written commun., 2001).

Geology

Rocks of Precambrian age to unconsolidated 

alluvium of Quaternary age underlie the upper 

Gunnison River watershed (fig. 4). The oldest rocks 

are in the eastern one-half (western flank of the 

Sawatch Range) and central portions of the watershed. 

Sedimentary rocks are exposed in central and northern 

locations, ranging from Paleozoic to Cretaceous in 

age (Green, 1992; Tweto, 1979). Erosion has exposed 

these sedimentary rocks as the primary feature 

forming many of the mountain sides and stream drainages in the central part of the watershed. Many of 

the taller mountains, like those in the Sawatch Range, 

are formed by Precambrian granite as well as by 

younger, Tertiary-age basalt caprock (Red Mountain) 

and laccolith intrusions (Mount Crested Butte and 

Whetstone Mountain). Tertiary igneous rocks, 

including ash flows, tuff, breccia, conglomerates, 

basalt, and other intrusive bodies, are the dominant 

rock types in the southern one-half and much of the 

northwestern sections of the watershed. The youngest 

formations include unconsolidated alluvium and 

glacial and landslide deposits of Quaternary age. The 

Table 1. Land use for the upper Gunnison River watershed

[Fegeas and others, 1983; refined by Hitt, 1995; mi2, square miles]

Land 

use

Area

(mi2)

Percentage of

study area

Agriculture 92.3 2.33

Barren land or tundra 308.8 7.79

Forest 2,258.8 56.97

Mining 0.7 0.02

Rangeland 1,272.8 32.10

Water or wetland 25.8 0.65

Urban or built-up 5.7 0.14
STUDY AREA 7

MEAN MONTHLY DISCHARGE, I N 

CUBIC FEET PER SECOND

OCTOBER

NOVEMBER

DECEMBER

JANUARY

FEBRUARY

MARCH

APRIL

MAY

JUNE

JULY

AUGUST

SEPTEMBER

500

1,000

1,500

2,000

2,500

0

WATER YEAR 1999

50

45

97

107

103

Site number

Gunnison Rive r

0 5 1 15 2 25 MILES 10 20

0 5 10 15 20 25 KILOMETERS

Crested Butte

Gunnison

Lake City

 50 (WY 1970-99)

29 (WY 1970-72)

14 (WY 1970-99)

61 (WY 1970-99)

58 (WY 1980-86)

24 (WY 1980-99)

107 (WY 1970-99)

45 (WY 1970-99)

105 (WY 1970)

76 (WY 1970)

69 (WY 1970-81)

68 (WY 1970)

5 (WY 1992-98)

37 (WY 1970-72, 

1979-81,1993-99)

83 (WY 1993-99)

Tomich

Blue Mesa Reservoir i Creek

Morrow Point

Reservoir

Crystal Reservoir

Taylor River

Slate River

Cocheto pa Creek

Ceboll a Creek

Q uartz Cre ek

Ohio Creek

Cimarron Rive r

Wil low Cr eek

Soap Creek

We st Elk Crrek

Curecanti Creek

Pitkin

103 (WY 1970-72,

1992-99)

99 (WY 1970-99)

97 (WY 1970-99)

101 (WY 1987-92)

96 (WY 1987-99)

East River

41(WY 1970-99)

Taylor Reservoir

EXPLANATION

U.S. Geological Survey gaging station

Historical station (discontinued 

 prior to WY 1999)

Current station (operational as of WY 1999)

47 Site number (Appendix A) 

(WY 1980–86) Water years of operation

38°30'

107°30'

39°

107°

106°30'

38°

Figure 3. Location of selected U.S. Geological Survey streamflow-gaging stations and mean monthly 

discharge (water year 1999) for selected stations.
8 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

most common of these unconsolidated features are 

landslide deposits, present largely in the western 

portions of the watershed. The two largest glacial drift 

features, of the Pinedale and Bull Lake Glaciations, 

are located northeast of Taylor Park Reservoir. The 

two youngest formations within the unconsolidated 

surficial deposits of Quaternary age, modern alluvium 

and gravels and alluvium, are present in most major 

drainages. 

METHODS OF DATA ANALYSIS

Methods of water-quality data analysis 

for the upper Gunnison River watershed consisted 

of retrieving all available water-quality data, in 

electronic format, collected from October 1969 

to December 1999; performing quality-assurance 

measures; and presenting summary statistics, 

temporal and spatial trends, and comparisons to 

Federal and State standards. 

Phm

Phm

Phm

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl

Tpl Tpl

Tpl

Tpl

Tpl

YXg

YXg

YXg

YXg

YXg

YXg

Tbb

Tbr

Tbb

Tbb

Tbb

Tbb

Tbb

Tbb

Tbr

Tbr

Tbr

Tbr

Tbr

Kmv

Kmv

Kmv

Kmv

Kmv

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

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Taf

Taf

Taf

Taf

Taf

Taf

Taf

Taf

Xb

Xb

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Xb

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Xb

Xb

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Xb

Xb

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Xfh

Xfh

Xfh

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Tiql

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Tial

Tiql

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Tial

Tial

Qd

Ql

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Tbrt Tbrt

Ql

Ql

Qd

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Ql

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Qd

Qd

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Ql Ql

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Jm

Jmw

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Jmj

Jmj

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Jmj Jmj Jmj

Tial

Xg

Xg

Xg

Xg

Xg MDO

MDO

Me

Me

Me

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Me

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Me

Me

Xm Tmi

Tmi

Tmi

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Tmi

Tmi

Tmi

Tmi

Tmi

Tmi

Tmi

Qg

Qg

Qg

Qg

Qg

Qg

Qg

Qa

Qa

Qa

Qa Qa

Xg

Xg

Xg

Xg

Xg

Xg

Xg

Xg

Xg

Xg

Xg

Xg

Tial

Tial

Tial

Tiql

Xg

Yg

Tki

Km

Km

Km

Km

Km

KJde

KJdj

KJdj

Km

KJde

KJde

Km

Km

KJdj

KJdj

Kd

Kd

Kd

Kd

Kdb Kdb

Qg

KJdw

Km

Km

Km

Tos

Tos

Tos

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Tos Tos

Tos

Tos

Xm

Xm

hmb

hmb

Xm

Km

Km

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KJdj KJdj

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Two

Two

Two

Te

Te

KJdm

Jme

hmb

hmb

hmb

hmb

hm

Tkec

Tkec

Qdo

Crested 

 Butte

Gunnison

Lake City

Pitkin

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

38o

107o30'

38o

30'

39o

107o

106o30'

Figure 4. Geology of the upper Gunnison River watershed.
METHODS OF DATA ANALYSIS 9

Qg

Qa Modern alluvium

Qd

Tpl

Taf

Kmv

Tiql

Tial

Ql

Tbrt

Km

KJde

KJdj

Kd

Kdb

KJdw

Tos

Tmi

Tui

Tbr

Tbb

Two

Te

KJdm

Tki

Tkec

Qdo

Gravels and alluvium

Glacial drift of Pinedale and Bull Lake Glaciations

Older glacial drift

Landslide deposits

Unconsolidated surficial deposits of Quaternary age

Sedimentary rocks of Tertiary age

Oligocene rocks

Wasatch Formation

Eocene prevolcanic rocks

Basalt flows and tuff, breccia, and conglomerate

Igneous rocks of Tertiary age

Rhyolitic intrusive rocks and flows

Ash-flow tuff of late-volcanic bimodal suite

Ash-flow tuff of main volcanic sequence

Intra-ash-flow andesitic lavas

Intra-ash-flow quartz latitic lavas

Pre-ash-flow andesitic lavas, breccias, tuffs, and 

 conglomerates

Upper Tertiary intrusive rocks of 20 Ma

Upper Tertiary intrusive rocks of 20 – 40 Ma

Sedimentary and igneous rocks of early Tertiary

 and Late Cretaceous age

Telluride conglomerate

Laramide intrusive rocks

Sedimentary rocks of Cretaceous age

Dakota Sandstone

Mesaverde Group, undivided

Mancos Shale

Dakota Sandstone and Burro Canyon Formation

Sedimentary rocks of Cretaceous and Jurassic ages

Dakota and Morrison Formations

Dakota, Burro Canyon, Morrison, and Junction 

 Creek Formations

Dakota, Burro Canyon, Morrison, and Wanakah

 Formations

Dakota, Burro Canyon, Morrison, Wanakah, and 

 Entrada Formations

EXPLANATION

Phm

Jmj

Jmwe

Jmw

Jme

hm

Sedimentary rocks of Jurassic age

Morrison Formation and Junction Creek Sandstone

Morrison Formation and Wanakah Formation

Morrison Formation and Entrada Sandstone

Morrison, Wanakah, and Entrada Formations

hmb

Me

MDO

eam

Xb

hb

Xfh

Yg

Yam

Xg

Xm

YXg

Sedimentary rocks of Permian and Pennsylvanian age

Maroon Formation

Sedimentary rocks of Pennsylvanian age

Minturn Formation

Belden Formation

Minturn and Belden Formations

Sedimentary rocks of Pre-Pennsylvanian Paleozoic age

Leadville, Gilman, Dyer, Parting, Fremont, Harding, 

 Manitou, Dotsero, Peerless, and Sawatch Formations

Leadville, Gilman, Dyer, Parting, Fremont, Harding, and 

 Manitou Formations

Igneous rocks of Cambrian age

Alkalic and mafic intrusive rocks in small plutons, 

 and diabase dikes

Metamorphic rocks of Precambrian age

Igneous rocks of Precambrian age

Biotite gneiss, schist, and migmatite

Felsic and hornblende gneisses

Granitic rocks of 1,400 Ma

Alkalic and mafic rocks in small plutons, and 

 diabase and gabbro dikes

Granitic rocks of 1,700 Ma

Mafic rocks of 1,700 Ma

Granitic rocks of 1,400 and 1,700 Ma

MA, mega-annum

Figure 4. Geology of the upper Gunnison River watershed—Continued.
10 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Data Sources

The data analyzed in this report were collected by Federal and State agencies: USGS, USEPA, 

CDPHE, NPS, USFS, and the Bureau of Reclamation. 

The data set consists of water-quality and waterquantity information for surface and ground water. 

Data were obtained in electronic format from the 

USGS National Water Information System (NWIS) 

and the USEPA Storage and Retrieval (STORET) 

databases. 

Data for 779 sites were retrieved from NWIS 

and STORET: 680 surface-water sites (including 

lakes and reservoirs) and 99 ground-water sites. 

Approximately 727 different constituents or properties 

were included in the retrieval. Substantially fewer than 

727 constituents were analyzed and presented in this 

report. These were field properties (water temperature, 

pH, dissolved oxygen, and specific conductance), 

major ions, nutrients, trace elements, streambed sediment, suspended sediment, chlorophyll, biochemical 

oxygen demand, and fecal coliform. The period of 

record varied for water-quality sites, many of which 

had limited data, often only one sample. Many USGS 

surface-water-quality sites also measured instantaneous discharge, daily discharge, and stream stage. 

There were substantially fewer ground-water sites than 

surface-water sites with water-quantity data. Groundwater-level data were compiled for 37 wells in the 

basin.

Data Quality Assurance

Prior to analysis, several quality-assurance 

measures were taken. The initial quality-assurance 

measures were used to identify gross errors in the 

data. The USEPA has established typical ranges for 

many constituents and properties, which have been 

used as a quality-assurance guideline for data entered 

into STORET since 1983 (National Park Service, 

1998). All data obtained from STORET and NWIS 

were checked using these guidelines. Data values also 

were checked to ensure that they fit into the context 

of other concentrations identified in a given sample. 

Dissolved concentrations were checked to be less than 

or equal to total concentrations when both total and 

dissolved concentrations were reported for a given 

sample. An ion balance was calculated for each 

sample with adequate data, which provided an 

effective method to check the accuracy of major 

dissolved constituent concentrations. An ion balance 

is a charge balance of a water sample, commonly 

calculated in milliequivalents per liter.

Concentration of cations in milliequivalents ≅

Concentration of anions in milliequivalents

Cations: calcium, magnesium, sodium, potassium

Anions: sulfate, chloride, fluoride, carbonate

A water-quality value identified as suspect 

by any data-quality-assurance measure was evaluated 

individually, taking into account the collection location, time of year, and other samples gathered at, or 

near, the site. In several cases, a value outside the 

range of STORET guidelines was actually determined 

to be correct. This determination was most common 

at sites located at the outlet of a particular abandoned 

mine in which trace-element concentrations were 

above the typical maximum value defined by 

STORET. At the conclusion of the data-qualityassurance measure, eight data values were deleted 

and one was corrected.

Data Compilation and Comparison

Methods described by Mueller and others 

(1995) were used to combine equivalent nitrogen 

and phosphorus species. Equivalent nitrogen and 

phosphorus species were combined because nutrient 

data were collected and reported by different agencies 

that use different laboratory methods and sampling 

and reporting conventions. For example, within the 

entire data set, nitrate nitrogen data were reported 

as dissolved nitrate as nitrogen, dissolved nitrate as 

nitrate, and total nitrate as nitrogen. Thus, nutrient 

species are summarized in this report as follows: 

ammonia as nitrogen (hereinafter referred to as 

“ammonia”), nitrite as nitrogen (hereinafter referred to 

as “nitrite”), nitrate as nitrogen (hereinafter referred to 

as “nitrate”), dissolved orthophosphate as phosphorus 

(hereinafter referred to as “orthophosphate”), total 

phosphorus for surface-water analysis, and dissolved 

phosphorus for ground-water analysis. At pH 9.24, 

the transformation of aqueous ammonia, NH3, to 

ammonium ion, NH4

+, is half complete, so in most 

natural water (pH lower than 9.24), ammonia nitrogen 

would primarily be in the ammonium ion form (Hem, 

1992). Aqueous ammonia (hereinafter referred to 

as “un-ionized ammonia”) was computed using pH, 
METHODS OF DATA ANALYSIS 11

water temperature, concentration of ammonium ion, 

and an equilibrium constant. The CDPHE has not 

established in-stream water-quality standards for 

the ammonium ion but has established an in-stream 

chronic standard for aqueous ammonia (un-ionized 

ammonia).

Major-ion concentrations were compiled to 

develop water types for water-quality sampling sites. 

Water types were calculated based on the percentage 

of milliequivalents of the major ions present within 

each sample. For those samples that exhibit a predominant water type, the cation and anion that makes up 

more than 50 percent of the total milliequivalents of 

cations and anions are identified. A number of samples 

had mixed water types, when no single cation or anion 

constitutes 50 percent or more of the totals (Hem, 

1992). The cations and anions of a mixed water type 

are identified in order from highest to lowest in total 

percentage to their respective sums of cations and 

anions.

After compilation, the water-quality data were 

compared to standards (or guidelines) and land-use 

classifications. Stream-water-quality data were 

compared to CDPHE in-stream water-quality standards, which are based on the stream reach classifications: cold-water aquatic life, recreation, water supply, 

and agriculture. A number of the trace elements have 

Table Value Standards (TVS), which are site-specific 

in-stream standards calculated using stream hardness. 

TVS equations use a stream hardness value calculated 

from the “lower 95th-percent confidence limit of the 

mean hardness value at the periodic low-flow criteria 

determined from a regression analysis of site-specific 

data” (Colorado Department of Public Health and 

Environment, 1999). In this study, the annual low-flow 

period was defined as October through March. When 

there were more than five hardness values at a given 

sampling site during the low-flow period, the lower 

95th-percent confidence limit of the mean hardness 

value was used in the TVS equation. If fewer than five 

samples were available during the low-flow period, the 

mean of the low-flow hardness values was used in the 

TVS equation. If there were no hardness samples 

available for the low-flow period, all hardness values 

were used and a lower 95th-percent confidence limit 

of the mean was determined (for five or more available 

non-low-flow samples). If fewer than five non-lowflow samples were available, the mean hardness of 

non-low-flow samples was used in the TVS equation.

The CDPHE has set chronic and acute instream standards for trace elements. According to the 

CDPHE (Colorado Department of Public Health and 

Environment, 1999), “chronic represents the level that 

protects 95 percent of the genera from chronic effects 

of metals that may include the following: demonstrable abnormalities and adverse effects on survival, 

growth, or reproduction,” and “acute represents half 

the concentration that is lethal to 50 percent of the test 

organisms in a 96-hour period.” For a given constituent, acute standards are usually higher than the 

chronic standards.

 Ground-water-quality data were compared to 

the USEPA maximum contaminant levels (MCL’s) and 

Secondary Drinking Water Regulations (SDWR). The 

USEPA MCL’s are enforceable standards for public 

water-supply systems but are not enforceable for individual domestic wells. SDWR’s are nonmandatory 

standards established to manage esthetic qualities 

(taste, odor, color) for public water supplies. Comparisons of ground-water-quality data in the upper 

Gunnison River watershed to USEPA MCL’s are 

offered only as a point of reference. 

Land-use classifications for water-quality 

sampling sites were determined based on comparison 

of site location to the land-use distribution map (fig. 2) 

and by incorporating recent changes (typically urban 

development) from upstream and surrounding landuse practices. Four land-use classifications were used: 

agriculture, forest, rangeland, and urban or built up. 

Temporal Trend Analysis

Trend analyses were performed using the 

seasonal Kendall test (Helsel and Hirsch, 1993) for 

sites having at least 5 years of quarterly data, a period 

of record ending within the last decade, and less than 

50 percent censored data (below laboratory reporting 

level). This analysis measured the monotonic relation 

between constituent concentration and time. Because 

the analysis is rank-based, it is resistant to the effects 

of small sample size, censored data, and non-normal 

population distributions. A positive correlation was 

identified if the constituent concentration increased 

more often than it decreased over time. In this report, 

a trend was determined to be present when the p-value 

of the statistical test was less than the decision level 

(alpha-level) of 0.05. The smaller the p-value, the 
12 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

stronger the evidence for rejection of the null 

hypothesis (Helsel and Hirsch, 1993). For this report, 

a p-value below 0.05 is sufficient evidence for rejection of the null hypothesis which states that no relation 

between concentration and time is present. Where 

instantaneous discharge data were available, flowadjusted concentrations were used in the Kendall’s 

tau analysis using a locally weighted scatterplot 

smoothing (LOWESS). A detailed discussion of 

Kendall’s tau and its application is included in 

Helsel and Hirsch (1993). 

 Due to data availability, several of the trend 

analyses were conducted over a short time period, 5 to 

10 years. In many cases, longer time periods may be 

required to identify a trend, particularly trends that are 

small in magnitude. In order to identify a trend, the 

change in concentration with time must be larger than 

the variability inherent in a given data set. Thus, trends 

may be present that are not identified due to the variability in the data. Conversely, trends that are identified over a 5-year period may not continue over a 

longer period, such as 10 years.

SURFACE-WATER QUALITY

Surface-water-quality data were collected and 

compiled at 482 sites located on streams and rivers in 

the upper Gunnison River watershed. Numerous agencies, over varying periods of record, collected a variety 

of water-quality data at these 482 sites. The USGS and 

NPS collected surface-water-quality data at the most 

sites, having sampled 192 and 168 sites, respectively. 

During the 1990’s, data were collected at 118 sites, 

whereas during the 1980’s and 1970’s, data were 

collected at 151 and 324 sites, respectively. More than 

one-half (255) of the sites had only one water-quality 

sample collected. During the 1970’s, 217 sites had 

only one water-quality sample collected, and during 

the 1990’s, 20 sites had only one water-quality sample 

collected. In comparison, during the entire period 

of study, 6.4 percent (31) of the total sites had more 

than 100 samples collected. Water-quality data for the 

upper Gunnison River watershed are summarized in 

table 2. Specific sites discussed or shown in figures are 

listed in Appendix A. Field properties were collected 

at nearly all surface-water sites, and major ions, nutrients, and trace elements also were commonly 

collected. 

Field Properties 

Temperature affects the life cycles and activity 

of biota in an aquatic environment (Allan, 1996) 

and the rate and equilibria of chemical reactions. 

Surface-water temperature in the upper Gunnison 

River watershed ranged between –0.7° and 22°C from 

October 1989 to December 1999 (table 2). Spatially, 

median water temperatures usually were lower in 

headwater areas compared to areas farther downstream. The highest median water temperatures were 

measured on the main stem of the Gunnison River, 

downstream from the city of Gunnison, and at the 

mouth of several other tributaries to the Aspinall Unit. 

Only 11 samples had water temperatures exceeding 

the CDPHE in-stream standard of 20°C. These 

measurements were made during summer periods at 

two sites on Tomichi Creek (104 and 107) and one 

site on Cochetopa Creek (24). One water-temperature 

measurement at site 104 and eight water-temperature 

measurements at site 107 exceeded 20°C; however, all 

were 22°C or less. Two exceedances at site 24 were 

recorded and both water-temperature measurements 

were 20.5°C. Differences in temperature with respect 

to land use are not presented because differences can 

be attributed to other factors such as shading, stream 

gradient, elevation, season, and streamflow rather than 

land use.

Dissolved oxygen is important in maintaining 

healthy stream biota as oxygen is necessary for the 

survival of many aquatic organisms. During the 

1990’s, no site in the watershed had a median 

dissolved-oxygen concentration less than the 

minimum CDPHE standard of 6 mg/L. Dissolvedoxygen concentrations were typically near saturation. 

Differences in dissolved-oxygen concentration among 

sites can be attributed to differences in physical variables such as temperature and reaeration rather than 

land-use practices. Six stream-water-quality sites had 

adequate dissolved-oxygen data to support a flowadjusted seasonal Kendall’s tau test for temporal trend 

analysis; however, no trends were identified, as shown 

in table 3.

Acidic or basic streams can affect biotic 

communities by reducing numbers of species and individual organisms (Allan, 1996). Few pH values were 

outside the range defined by CDPHE in-stream standards (6.5 to 9.0); three pH values were more acidic 

than standards, and only two values were more basic. 

The sites with pH below 6.5 were located on Henson 
SURFACE-WATER QUALITY 13

Table 2. Summary of the number of analyses, minimum, median, and maximum concentrations for surface-water-quality 

samples in the upper Gunnison River watershed

[No., number; mg/L, milligrams per liter; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; NTU, 

nephelometric turbidity units; mg/m2, milligrams per square meter; mL, milliliter; <, less than; --, not available]

Property or constituent

(reporting units)

No. of

analyses/

No. of

censored

values,

1970–99

October 1989 to December 1999

No. of

analyses/

No. of

censored

values

No. of

sites

Minimum

value

Median

value

Maximum

value

In-streamsegment 

standards1

Field properties

Temperature (oC) 10,567/6 5,248/4 134 –0.7 10.54 22 20

Oxygen, dissolved (mg/L) 5,828/1 2,393/0 122 2.6 8.88 16.64 6.0

pH, field (standard units) 3,345/83 1,614/0 115 3.43 7.9 9.4 6.5–9.0

Specific conductance (μS/cm) 7,158/5 2,589/0 90 24 175 921 --

Turbidity (NTU) 1,181/0 174/0 15 0.1 1.5 35 --

Alkalinity (mg/L as CaCO3) 404/0 367/0 30 16 79 175 --

Major ions

Bicarbonate, dissolved 

(mg/L as HCO3)

207/0 207/0 20 21 95 182 --

Calcium, dissolved (mg/L) 917/0 444/0 31 6.2 26.5 60 --

Chloride, dissolved (mg/L) 536/18 377/14 29 <0.1 0.89 4.4 --

Chloride, total (mg/L) 469/2 0/0 -- -- -- -- 250

Fluoride, dissolved (mg/L) 688/123 378/4 30 <0.1 0.15 0.5 --

Magnesium, dissolved (mg/L) 753/3 444/0 31 0.51 5.1 13 --

Potassium, dissolved (mg/L) 668/1 378/0 30 0.19 0.9 5.6 --

Silica, dissolved (mg/L) 622/0 378/0 30 2.8 6.8 22 --

Sodium, dissolved (mg/L) 722/0 378/0 30 0.6 3.7 10 --

Sulfate, dissolved (mg/L) 549/16 377/0 29 4.3 17 53

Sulfate, total (mg/L) 1,020/70 258/41 33 5 18 260 250

Dissolved solids (mg/L) 557/0 359/0 28 27 112 218 --

Nutrients

Ammonia (mg/L as N) 2,330/1,119 1,228/657 100 <0.002 0.009 0.7 --

Nitrate (mg/L as N) 2,550/908 1,190/413 99 <0.005 0.07 2.55 10, 100

Nitrite, dissolved (mg/L as N) 858/563 775/561 56 <0.001 0.01 0.03 0.02, 0.05

Orthophosphate, dissolved

(mg/L as P)

2,736/600 2,028/562 85 <0.001 0.008 0.143 --

Phosphorus, total (mg/L as P) 3,357/748 2,258/380 117 <0.001 0.05 4.05 --

Un-ionized ammonia (computed

as mg/L)

734/0 427/0 56 0.000003 0.0003 0.008 0.02, 0.05

Trace elements

Aluminum, dissolved (μg/L) 322/169 256/162 38 Greater than 50 percent of 

data censored

Reporting levels of 50, 15, 

and 5

3,900 --

Arsenic, dissolved (μg/L) 227/112 56/51 23 Greater than 50 percent of 

data censored

Reporting levels of 1

5 --

Cadmium, dissolved (μg/L) 775/618 498/428 59 Greater than 50 percent of 

data censored

Reporting levels of 1, 0.3, 

0.25, and 0.14

19 Footnote 2
14 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Trace elements—Continued

Copper, dissolved (μg/L) 904/611 521/394 62 Greater than 50 percent of 

data censored

Reporting levels of 5, 4, 

and 1

4,700 Footnote 2

Chromium, dissolved (μg/L) 302/218 10/9 9 Greater than 50 percent of 

data censored

Reporting level of 1

2 Footnote 2

Iron, dissolved (μg/L) 1,097/298 465/115 71 <3 4

14 14,000 Footnote 3

Iron, total (μg/L) 407/14 252/0 23 10 220 6,400 Footnote 3

Lead, dissolved (μg/L) 880/690 495/455 56 Greater than 50 percent of 

data censored

Reporting levels of 1 and 5

19 Footnote 2

Manganese, dissolved (μg/L) 1,307/410 736/155 74 <1 5

10 1,200 Footnote 3

Manganese, total (μg/L) 379/88 248/35 23 <3 30 430 --

Mercury, dissolved (μg/L) 284/263 194/194 35 All data censored

Reporting levels of 0.2 and 0.1 

--

Nickel, dissolved (μg/L) 251/132 9/8 10 Greater than 50 percent of 

data censored

Reporting levels of 10 and 1

1.3 Footnote 2

Silver, dissolved (μg/L) 377/337 268/265 51 Greater than 50 percent of 

data censored

Reporting levels of 1, 0.32, 

and 0.2

0.2 Footnote 2

Selenium, dissolved (μg/L) 284/224 187/183 40 Greater than 50 percent of 

data censored

Reporting levels 8, 5, and 1

2.8 --

Uranium, natural dissolved 

(μg/L)

333/32 61/28 37 <1 1 630 Footnote 3

Zinc, dissolved (μg/L) 950/433 547/280 64 Greater than 50 percent of 

data censored

Reporting levels of 25, 20, 

10, 8, and 3

2,100 Footnote 2

Suspended sediment

Suspended sediment (mg/L) 385/0 385/0 40 0 48 205 --

Other parameters

Stream chlorophyll-a (mg/m2) 34/0 34/0 17 0.1 2.4 70 --

Biochemical oxygen demand 

(mg/L)

661/0 163/0 12 0.0 0.8 3.2 --

Fecal coliform (counts/100 mL) 3176/0 1070/0 79 0 7 3,500 Footnote 3

1

In-stream-segment standards from Colorado Department of Public Health and Environment, Water Quality Control Commission, 1999.

2Table value standard, which varies with hardness (see Colorado Department of Public Health and Environment, Water Quality Control Division, 1999). 3

Standard varies by stream reach (see Colorado Department of Public Health and Environment, Water Quality Control Division, 1999). 4

Median calculation omitted sites that utilized a reporting level of 100.

5Median calculation omitted sites that utilized a reporting level of 50 micrograms per liter.

Table 2. Summary of the number of analyses, minimum, median, and maximum concentrations for surface-water-quality 

samples in the upper Gunnison River watershed—Continued

[No., number; mg/L, milligrams per liter; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; μg/L, micrograms per liter; NTU, 

nephelometric turbidity units; mg/m2

, milligrams per square meter; mL, milliliter; <, less than; --, not available]

Property or constituent

(reporting units)

No. of

analyses/

No. of

censored

values,

1970–99

October 1989 to December 1999

No. of

analyses/

No. of

censored

values

No. of

sites

Minimum

value

Median

value

Maximum

value

In-streamsegment 

standards1
SURFACE-WATER QUALITY 15

Creek and Palmetto Gulch in the Lake City area 

(sites 52, 55, and 72—Appendix A). These sites 

are upstream from Lake City in a subbasin affected 

by historical mining, which can be reflected in the 

more acidic pH values. The two sites with single 

values greater than pH 9.0 were located on the 

Cimarron River (pH of 9.05, site 15—Appendix A) 

and Cebolla Creek at Hot Springs Ranch (pH of 9.4, 

site 7). Sufficient data for trend analysis were available 

for 14 sites in the basin (table 3); no trends were 

identified.

Specific conductance is a measure of the ability 

of water to conduct an electric current. In natural 

water, specific conductance commonly is related to 

the concentration of dissolved solids (Hem, 1992). 

At least one specific-conductance measurement was 

made at 605 sampling sites since 1970. At sites with a 

minimum of five samples since 1970, specific conductance ranged from 41.5 to 3,200 μS/cm. Only seven 

sampling sites had a median specific-conductance 

value greater than 500 μS/cm. Four of the sites 

were near hot springs (sites 8, 11, 12, and 108—

Appendix A), and the remaining three sites were 

near Crested Butte (sites 22 and 86) or on Squaw 

Creek near Cimarron (site 90). At sites with at least 

five measurements since October 1989, median 

specific conductance ranged from 49 to 848 μS/cm 

(fig. 5). Only one site, Squaw Creek above Cimarron 

(site 90), had a median specific conductance greater 

than 500 μS/cm. Higher specific-conductance values 

are probably related to the geology and soils in the 

Squaw Creek–Cimarron areas.

Major Ions

Major ions summarized in this report are 

common constituents dissolved in most natural water 

and include bicarbonate, calcium, chloride, fluoride, 

magnesium, potassium, silica, sodium, and sulfate. 

Table 3. Seasonal Kendall trend-analysis results for dissolved oxygen and pH in the upper Gunnison River watershed 

Site name and number

(Appendix A)

Period of

record

Number of

samples

Flow

adjustment p-Value Trend

direction

Median

value

Dissolved oxygen

(milligrams per liter)

Slate River near Crested Butte, 83 1994–98 30 Yes 1.0 None 10.3

East River below Cement Creek near Crested Butte, 37 1994–99 85 Yes 0.68 None 9.7

East River at Almont, 41 1991–99 51 Yes 0.24 None 9.7

Taylor River at Almont, 99 1994–99 31 Yes 0.48 None 9.6

Tomichi Creek at Gunnison, 107 1991–99 40 Yes 0.73 None 9.3

Gunnison River below Gunnison Tunnel, 50 1995–99 68 Yes 0.11 None 9.8

pH

(standard units)

Slate River above Oh-Be-Joyful Creek near Crested Butte, 78 1995–99 26 No 1.0 None 7.8

Slate River above Coal Creek near Crested Butte, 79 1995–99 36 No 0.68 None 7.6

Slate River near Crested Butte, 83 1995–99 39 No 0.89 None 7.6

Slate River above the East River near Crested Butte, 88 1995–99 30 No 0.59 None 7.6

East River below Gothic, 33 1995–99 32 No 1.0 None 8.1

East River above Crested Butte, 34 1995–99 30 No 0.86 None 8.0

East River above Slate River near Crested Butte, 36 1995–99 34 No 1.0 None 8.2

East River below Cement Creek near Crested Butte, 37 1994–99 86 No 0.57 None 8.3

East River at Almont, 41 1991–99 52 No 0.71 None 8.3

Taylor River at Almont, 99 1994–99 31 No 0.06 None 8.1

Tomichi Creek at Gunnison, 107 1991–99 42 No 1.0 None 8.2

Gunnison River near Gunnison, 45 1995–99 28 No 1.0 None 8.2

Gunnison River at County Road 32 below Gunnison, 47 1995–99 53 No 0.67 None 8.1

Gunnison River below Gunnison Tunnel, 50 1995–99 67 No 0.55 None 8.0
16 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Pitkin

Gunnison Rive r

24

96

101

99

98, 99

41

44

42

70, 71

37

87, 88

34

33

66

78

83

85

107

46, 47, 48 45

49 91

113

112

109

74

73

28

4

3

18, 19

16

17

9

61

62

90

5

106°30'

39°

107°

107°30'

38°

38°30'

0 5 1 15 2 25 MILES 10 20

0 5 10 15 20 25 KILOMETERS

Gunnison

Cochetopa Creek

Q uartz Creek

Tomich i Creek

Blue Mesa Reservoir

Ceboll a Creek

Crystal Reservoir

Cimarron

Rive r Squaw Creek

50, 51

14

Lake City

Slate River

Crested Butte

Taylor River

East Rive

O

r

hio Creek

36

35

EXPLANATION

Median specific conductance, in 

 microsiemens per centimeter at 

 25 degrees Celsius (with site number

 from Appendix A)

49 to 199

200 to 499

500 to 848

Lake Fork Gunn

ison River

79, 80, 81

56

103

Taylor Park

 Reservoir

84

Morrow Point

Reservoir

Figure 5. Spatial distribution of median specific conductance, October 1989 to December 1999.
SURFACE-WATER QUALITY 17

Unless specifically stated otherwise, ion concentrations discussed in this section refer to dissolved 

concentrations. These major ions are dissolved in 

water as a result of interactions among surface and 

ground water, geology, soils, aquifer material, and 

human activities.

In most stream reaches, the dominant ions in 

solution are the cation calcium and anion bicarbonate. 

During spring runoff (May–June), recently melted 

snow dilutes solute concentrations and produces 

water ionically similar to precipitation. Other natural 

and anthropogenic factors that may affect water 

quality are often masked during spring runoff. 

Calcium-bicarbonate type water was the most spatially 

dominant from July to April (nonspringtime runoff 

conditions) and was present in nearly all the reaches 

sampled. A calcium-bicarbonate type water reflects 

weathering of underlying geology and soil material. 

Calcium-sulfate type water is found exclusively in 

Henson Creek and the Lake Fork of the Gunnison 

River, upstream from Lake City, and is attributed to 

the weathering of sulfate-bearing rocks associated 

with historical mining. Other water types in the basin 

(calcium sodium mixed, carbonate; magnesiumcarbonate; calcium magnesium mixed, sulfate; 

sodium-carbonate; sodium, carbonate sulfate mixed; 

and sodium-sulfate) are less common than calciumcarbonate and calcium-sulfate water samples and 

reflect the weathering of underlying geologic material.

The CDPHE has established two in-stream 

standards for major ions in the upper Gunnison River 

watershed, 250 mg/L for both total chloride and total 

sulfate (Colorado Department of Public Health and 

Environment, 1999). Total chloride concentrations 

were well within in-stream standards, and only one 

total sulfate concentration (260 mg/L) exceeded the 

standard (table 2) and was measured at Indian Creek 

near Sargents (site 56—Appendix A). Total concentrations are determined from nonfiltered samples and 

contain both dissolved and particulate matter.

Hardness of water was computed from the sum 

of calcium and magnesium concentrations expressed 

as calcium carbonate (CaCO3). Calcium and magnesium commonly are the result of weathering of the 

underlying rocks and soils in a region. In the upper 

Gunnison River watershed, the hardness was generally 

low. Since WY 1990, the range of median CaCO3 

concentrations was between 21 and 240 mg/L. During 

the entire period of study, less than 30 percent of the 

sampling sites in the watershed had median hardness 

values greater than 100 mg CaCO3/L. There were 

large gaps in the spatial coverage of hardness data. 

However, based on the available information, sites 

located closer to headwaters in the watershed had 

the lowest hardness values, except Indian Creek in the 

upper Tomichi subbasin (sites 56 and 57). The highest 

hardness values were at sites classified as mining and 

rangeland. Increased hardness in water near mined 

areas may be due to increased weathering rates of 

rocks, which generally have more surface area 

exposed to water and oxygen after being mined. 

Forested sites had the lowest hardness values; 16 

of 20 forested sites had a hardness less than 60 mg 

CaCO3/L. The higher hardness concentrations in the 

rangeland areas are probably associated with underlying geology rather than land-use practices.

Nutrients

Nutrients (ammonia, nitrate, nitrite, phosphorus, 

and orthophosphate) in surface water can originate 

from various sources and are essential to most aquatic 

life; however, excessive nitrogen and phosphorus 

concentrations can produce an overgrowth of algae, 

which can lead to degraded aquatic habitat and a lower 

dissolved-oxygen concentration. In addition, excessive 

nitrogen concentrations are toxic to fish when in 

the form of un-ionized ammonia. Excessive nitrate 

concentrations also can be toxic to humans, causing 

methemoglobinemia in infants (Klaassen, 1996). 

Concentrations of nutrients originate from both natural 

and anthropogenic sources. The major factors causing 

excessive nutrient concentrations are human activities, 

including the combustion of fossil fuels, application 

of fertilizers, phosphate detergents, discharge of 

effluent from wastewater-treatment facilities, and 

seepage from septic systems and animal feedlots. 

Natural sources of nutrients include erosion of rocks 

and soils containing phosphorus minerals, decomposition of organic matter, and atmospheric deposition.

Nutrient samples were collected at surfacewater sites in most stream reaches within the watershed. Summary statistics for these nutrients are listed 

in table 2. Phosphorus data were collected at more 

sites and more frequently than other nutrient data. 

Nitrite and orthophosphate have been excluded from 

the analysis of spatial distribution and temporal trends 

due to the large number of nitrite and orthophosphate 

concentrations reported as less than a laboratory 

reporting level (censored values) (table 2).
18 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Spatial Distribution and Comparison to State 

Standards

Spatial distribution of nutrient concentrations 

and comparison to CDPHE in-stream standards were 

evaluated for sites with five or more samples since 

WY 1990. Most sites sampled for nutrients were 

located along the Slate River and East River near 

Crested Butte and along the Gunnison River from 

the confluence of the East and Taylor Rivers to the 

western edge of the watershed. Fewer sites with 

nutrient data were located from upstream reaches 

of the watershed (Lake Fork of the Gunnison River, 

Cebolla Creek, Ohio Creek, Tomichi Creek, Quartz 

Creek, and Cochetopa Creek).

Spatial distributions of median concentrations 

for ammonia, nitrate, and total phosphorus are illustrated in figures 6, 7, and 8, respectively. Median 

ammonia concentrations were relatively low, and 

many of the sampling sites had more than 50 percent 

censored data. Sites with the highest median ammonia 

concentrations were on the Cimarron River, near the 

confluence with the Gunnison River (fig. 6). Reasons 

for the higher concentrations in this area are unknown. 

Similar to ammonia, many sites in the upstream 

reaches of the watershed that were sampled for nitrate 

concentrations had more than 50 percent censored 

data. Of the sites having less than 50 percent censored 

nitrate concentration data, three sites had median 

concentrations (0.44, 0.25, and 0.24 mg/L) greater 

than 0.21 mg/L (fig. 7, sites 90, 85, and 87). Sites 

sampled for total phosphorus had fewer median values 

that were below censoring levels than sites sampled for 

either ammonia or nitrate. Sites along the Slate and 

East Rivers near Crested Butte had lower total phosphorus median values than sites in areas farther 

downstream in the watershed, particularly along 

the Gunnison River and its tributaries, downstream 

from Gunnison (fig. 8). Sites with total phosphorus 

median values greater than 0.15 mg/L were on the 

Gunnison River downstream from Crystal Reservoir, 

Squaw Creek, and the Cimarron River, Cochetopa 

Creek, and the Gunnison River downstream from 

Gunnison.

CDPHE in-stream water-quality standards 

for selected stream reaches are based on water-use 

classifications in the upper Gunnison River watershed (Colorado Department of Public Health and 

Environment, 1999). In-stream standards for nitrite, 

nitrate, and un-ionized ammonia vary spatially 

(according to stream reach) within the watershed. 

For example, in selected tributaries of the Gunnison 

River, an in-stream standard for nitrite was established 

at 0.02 mg/L, whereas the remainder of the watershed 

was set at 0.05 mg/L for nitrite concentration. No 

in-stream standards for nitrite were exceeded in 

the watershed. Three stream reaches have nitrate 

in-stream standards of 100 mg/L, and the standard for 

the remainder of the stream reaches is set at 10 mg/L. 

All nitrate concentrations were below 10 mg/L. All 

computed un-ionized ammonia concentrations were 

well below the chronic standard of 0.02 mg/L, and the 

maximum concentration was an order of magnitude 

below the standard.

The CDPHE has not established in-stream 

standards for total phosphorus; however, for 

controlling eutrophication, the USEPA has recommended that concentrations of total phosphorus be 

less than 0.1 mg/L in rivers and less than 0.05 mg/L 

in rivers that directly enter lakes and reservoirs 

(U.S. Environmental Protection Agency, 1986). More 

than 30 percent of stream sites in the watershed (23 of 

61 sites) had median total phosphorus concentrations 

greater than the USEPA recommendations. These 

sites are located on the Cimarron River and tributaries 

(sites 15, 16, 17, 19, and 90); tributaries to Blue Mesa, 

Morrow Point, Crystal Reservoirs (sites 4, 6, 7, 9, 28, 

73, 74, 91, 92, 94, 109, 112, and 113); the Gunnison 

River downstream from Gunnison (46, 49, and 51); 

Mill Creek (tributary to Ohio Creek, site 65); and 

Cochetopa Creek (site 23).

Temporal Trends

Temporal trend analyses were conducted for 

ammonia, nitrate, and total phosphorus at sites that 

met the statistical requirements discussed in the 

“Temporal Trend Analysis” section. These statistical 

requirements were met at two sites containing 

ammonia data, eight sites containing nitrate data, and 

four sites containing total phosphorus data. Sites with 

nitrite, orthophosphate, and un-ionized ammonia data 

did not meet statistical requirements.

At sites analyzed for temporal trends, the period 

of record was either 5 or 6 years of data, beginning in 

the mid-1990’s and ending in 1999 (table 4). Neither 

nitrate nor total phosphorus had statistically significant 

trends at any site. However, at the Slate River near 

Crested Butte (site 83), ammonia concentrations had a 

statistically significant upward trend, with a p-value of 

0.016 (table 4). The smaller the p-value, the stronger 

the evidence for rejection of the null hypothesis 

(Helsel and Hirsch, 1993), which states that no 
SURFACE-WATER QUALITY 19

EXPLANATION

Median ammonia concentration, in 

 milligrams per liter (with site number

 from Appendix A)

0.22 to 0.24

0.12 to 0.21

0.051 to 0.11

Less than 0.051

Less than 0.1 (censored)

Less than 0.015 (censored)

Crested Butte

Gunnison

Lake City

Pitkin

Tomich i Creek

Gunnison Rive r

Blue Mesa Reservoir

Morrow Point

Reservoir

Crystal Reservoir

Lake Fork Gunnison River

Taylor River

Slate River East River Cochetopa Creek

Ceboll a Creek

Q uartz Creek

Ohio Creek

Cimarron

Rive r

107°

106°30'

39°

38°30'

107°30'

38o

Taylor Park

 Reservoir

60

53

6

7

23

57

56

104

102

43

75

100

65

50

131

134

90

17 15 16

19 130 135

74132

124

125 123

115

92 48

47

46 107

71 45

70

44

99

98 41

42

37

13 87

88

36

35

40

33

34

83

80 84

79 81

66

78

85

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 6. Spatial distribution of median ammonia concentrations, October 1989 to December 1999.
20 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Lake City

Tomich

Morrow Point i Creek

Reservoir

Crystal Reservoir

Lake Fork Gunnison River

Cochetopa Creek

Ceboll a Creek

Cimarron

Rive r Squaw Creek

60

53

6

7

23

50

131

90 134

17 15 16

19 130 135

74132 Blue Mesa Reservoir

125 123

115

92 Gunnison Gunnison Rive r

Taylor River

East River

Q uartz Creek

Ohio Creek

65

48

47

46 107

71 45

44

99 41

98

42

37

13 88 87

70

Crested Butte

Slate River 36 85

35

40

33

34

83

80

84

79 81

66

78

Taylor Park

 Reservoir

100

Pitkin

102

43

75

57

56

104

38°30'

107°30'

39°

107°

106°30'

38°

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

0.21 to 0.44

0.12 to 0.21

0.051 to 0.11

Less than 0.051

Less than 0.5 (censored)

Less than 0.05 (censored)

EXPLANATION

Median nitrate concentration, in

 milligrams per liter (with site number

 from Appendix A)

Figure 7. Spatial distribution of median nitrate concentrations, October 1989 to December 1999.
SURFACE-WATER QUALITY 21

0.15 to 0.24

0.1 to less than 0.15

0.05 to less than 0.1

Less than 0.05

Less than 0.05 (censored)

Less than 0.01 (censored)

EXPLANATION

Median total phosphorus concentration,

 in milligrams per liter (with site number

 from Appendix A)

Lake City

Lake Fork Gunnison River

Cimarron

Rive r

60

38°

Morrow Point

Reservoir

Crystal Reservoir

38°30'

50

131

90 134 15 16

17

19 130

135

51 129

4

28

62

Blue Mesa Reservoir

Ceboll a Creek

107°30'

74

132

125

133

73 126

128127

124

109

Gunnison

Tomich i Creek

Gunnison Rive r

Cochetopa Creek

Ohio Creek

65

123 115

92

49

47

46 107

71

45

44

99 41 98

42

70

119

118

48 116 94

117

113

112

91

Taylor River

East River

104

37

87 88

Crested Butte

Slate River

107°

39°

13

85 36

35

40

33

34

83

84 80

79 81

66

78

106°30'

Taylor Park

 Reservoir

100

Pitkin

Q uartz Creek

56

102

43 75

23

57

6

7

9

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 8. Spatial distribution of median total phosphorus concentrations, October 1989 to December 1999.
22 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

relation between concentration and time is present. 

The Slate River near Crested Butte site is located 

immediately downstream from the towns of Crested 

Butte and Mount Crested Butte and may reflect 

recent population growth or other land-use changes 

in the area. The rate of change of the trend is small 

(0.017 mg/L/year). Un-ionized ammonia concentrations at this site are relatively low and well below 

CDPHE in-stream standards, presenting no apparent 

environmental concern.

Land-Use Comparison

Distribution of ammonia, nitrate, and total 

phosphorus concentration by agriculture, forest, rangeland, and urban land-use classifications is shown in 

figure 9. Most nutrient data were collected at urban 

sites, followed by rangeland sites.

Because the nutrient data were not normally 

distributed, nonparametric statistics were used to 

determine differences among land-use groups. 

Statistical comparison of the median concentrations 

between the land-use groups was accomplished using 

an unbalanced analysis of variance and Tukey’s 

multiple comparison test on the rank-transformed 

data (Helsel and Hirsch, 1993). Nitrate and total phosphorus were found to be different among agriculture, 

forest, rangeland, and urban land-use classified sites. 

Ammonia was not compared among the groups 

because more than 50 percent of the ammonia data 

was censored. Results of the multiple comparison 

test are represented by letters adjacent to the median 

values on the boxplots in figure 9. Plots with different 

letters adjacent to the medians (defined as multiple 

comparison groups) are statistically different at 

Table 4. Seasonal Kendall trend-analysis results for selected nutrient species in the upper Gunnison River watershed

[No., number; mg/L, milligrams per liter; --, not available] 

Site name and number

(Appendix A)

Period of

record

Number of

samples/

No. of

censored

values

Flow

adjustment p-Value Trend

direction

Magnitude of

trend slope

(mg/L

per year)

Median

concentration

(mg/L)

Ammonia

Slate River near Crested Butte, 83 1995–99 36/2 Yes 0.02 Upward 0.017 0.08

East River below Cement Creek near Crested 

Butte, 37

1994–99 80/37 Yes 0.84 None -- 0.01

Nitrate

Slate River above Coal Creek near Crested 

Butte, 79

1995–99 34/2 Yes 0.32 None -- 0.10

Slate River near Crested Butte 83 1995–99 36/0 Yes 0.67 None -- 0.12

Slate River above East River near Crested 

Butte, 88

1995–99 30/1 Yes 0.77 -- 0.13

East River above Crested Butte, 34 1995–99 28/2 Yes 0.48 None -- 0.09

East River below Cement Creek near Crested 

Butte, 37

1994–99 79/5 Yes 0.69 None -- 0.09

East River at Almont, 41 1994–99 37/8 Yes 0.22 -- 0.08

Gunnison River at County Road 32 below the 

City of Gunnison, 47

1995–99 51/12 Yes 0.67 None -- 0.06

Gunnison River below Gunnison Tunnel, 50 1995–99 63/12 Yes 0.90 None -- 0.06

Total phosphorus

East River below Cement Creek near Crested 

Butte, 37

1995–99 74/30 Yes 0.88 None -- 0.01

East River at Almont, 41 1995–99 32/15 Yes 0.89 None -- 0.01

Gunnison River at County Road 32 below the 

City of Gunnison, 47

1995–99 51/7 Yes 0.24 -- 0.03

Gunnison River below Gunnison tunnel, 50 1995–99 65/19 Yes 0.54 None -- 0.02
SURFACE-WATER QUALITY 23

EXPLANATION

Percentiles

(65)

Reporting level (RL)

- Multiple comparison 

 group

AMMONIA, IN

MILLIGRAMS PER LITER

NITRATE, IN

MILLIGRAMS PER LITER

TOTAL PHOSPHORUS, IN

MILLIGRAMS PER LITER

Agriculture Forest Rangeland Urban

10

1

0.1

0.01

0.001

RL = 0.02

 (65) (73) (255) (398) 

A

Agriculture Forest Rangeland Urban

10

1

0.1

0.01

0.001

RL = 0.01

 (65) (73) (255) (397)

B

Agriculture Forest Rangeland Urban

10

1

0.1

0.01

0.001

 (139) ( 210) (671) (434)

C

RL = 0.05

a

b

c

b

a a

b a b

90

75

50

25

10

a

Data values outside

 the 10th and 90th 

 percentiles

Number of samples

Figure 9. Distribution of (A) ammonia, (B) nitrate, and (C) total phosphorus concentrations by land-use classification 

for surface water, October 1989 to December 1999.
24 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

an alpha level of 0.05. In figure 9, multiple comparison groups with the same letters are not statistically 

different. If two letters are given (for example, ab), 

then the median is not statistically different from other 

groups with either of the letters (Mueller and others, 

1995). The Tukey test showed nitrate concentrations 

were significantly different between agriculture and 

forest and between agriculture and urban land-use 

classifications (fig. 9). No significant differences were 

identified between agriculture and rangeland (fig. 9). 

Although differences were identified between median 

nitrate values of some land uses, the median nitrate 

concentrations were low for all land-use classifications. Median concentrations of total phosphorus 

were greatest in rangeland and least in urban classifications. The multiple comparison test identified no 

differences for median total phosphorus concentrations between agriculture and forest classifications 

(fig. 9). Specific reasons for the higher concentrations 

in rangeland sites are unknown. However, most 

concentrations of ammonia and nitrate were less than 

the 0.1 and 0.6 mg/L national background concentrations (Mueller and others, 1995). With the exception 

of rangeland sites, most concentrations of total 

phosphorus were below the national background 

concentration of 0.1 mg/L (Mueller and others, 

1995).

Trace Elements 

Many trace elements are required, in small 

amounts, by plant and aquatic life. However, in 

larger concentrations, trace elements can be harmful 

to plants and animals and, in sufficient concentrations, 

to humans. Trace elements are most often defined as 

those elements that occur in concentrations below 

1 mg/L and are normally reported in micrograms per 

liter (μg/L). Unless specifically stated otherwise, traceelement concentrations discussed in this section refer 

to dissolved concentrations.

Trace elements enter the water column through 

both natural and anthropogenic sources. In the absence 

of anthropogenic influence, the types and relative 

concentrations of trace elements in surface water are 

related directly to the geology of a region. In the upper 

Gunnison River watershed, mining and urban areas 

have the potential to increase trace-element contributions to surface water. Active and historical mining 

exposes the underlying formations to water and air, 

resulting in increased physical and chemical weathering that alters the chemistry of the water contacting 

the exposed formation. Trace elements in urban areas 

are associated with industrial waste and processes, 

transportation, such as roads and vehicles, and many 

items used and found in homes, such as paint, piping, 

and plastics. 

Of the 73 trace elements in the data set 

(WY 1970 to December 1999), many had too few 

samples to support statistical analyses. For example, 

23 trace elements had fewer than 20 samples, over 

30 years and 611 sites. Since WY 1990, 837 samples 

at 99 sampling sites included at least one traceelement concentration. Selection of trace elements 

for analysis was based on sites with five or more 

samples or the availability of CDPHE water-quality 

standards. The selected trace elements were 

aluminum, arsenic, cadmium, chromium, copper, 

iron, lead, manganese, mercury, nickel, selenium, 

silver, uranium, and zinc. 

Spatial Distribution and Comparison to State 

Standards

The spatial distribution of trace-element 

samples was not evenly distributed within the 

watershed. The Slate, East, and Gunnison Rivers 

from Crested Butte to the city of Gunnison had more 

trace-element sampling sites than any other stream 

reach in the watershed. Since WY 1990, there were 

between 15 and 35 sites with five or more samples 

for most trace elements. Adequate data for analysis 

for arsenic and uranium were available at two sites. 

No sites had adequate data for analysis of chromium 

and nickel.

The distribution of median concentrations for 

cadmium, silver, and zinc (figs. 10, 11, and 12) is 

representative of the sampling locations and spatial 

distribution of concentrations for other trace elements 

in the watershed. Median concentrations of arsenic, 

lead, mercury, selenium, and silver were low or 

censored throughout the basin. Concentrations of 

aluminum, cadmium, copper, lead, manganese, and 

zinc had elevated concentrations near the town of 

Crested Butte and on Henson Creek upstream from 

Lake City. These were the only two areas in which 

elevated trace-element concentrations were consistently detected, and both are located downstream 

from historical mining areas. 
SURFACE-WATER QUALITY 25

0.3 to 1.0

Median less than 1.0 (censored)

Median less than 0.3 (censored)

EXPLANATION

Median cadmium concentration,

 in micrograms per liter (μg/L)

 (with site number from Appendix A)

H

Lake City enson Cr

53

60

38°

Cimarron

Rive r

2

38°30'

Morrow Point

Reservoir

Crystal Reservoir

15

107°30'

Blue Mesa Reservoir

Gunnison

Ohio Creek

92

48

47

107

71

45

65

Tomich i Creek

Cochetopa Cr eek

Q uartz Creek

104

44 42

98

99

41

Pitkin

75

43

East River

Taylor River

Crested Butte

Slate River

37

13

83

84 79

80

66

40

78

107°

39°

Taylor Park

 Reservoir

100

106°30'

57

56

23

Ceboll a Creek

7

6

61

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 10. Spatial distribution of median cadmium concentrations, October 1989 to December 1999.
26 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Median silver concentration,

 in micrograms per liter (μg/L)

 (with site number from 

 Appendix A)

EXPLANATION

Median less than 1.0 (censored)

Cochetopa Creek

Ceboll a Creek

7

Tomich i Creek

57

Pitkin

Q uartz Creek

75

43

G

Gunnison unnison Rive r

Taylor River

East Rive r

Ohio Creek

41

99

37

13

Crested Butte

Slate River

83 84

79

78

80

107°

39°

106°30'

Taylor Park

 Reservoir

H

Lake City enson Cr

60

53 38°

2

Cimarron

Rive r

Morrow Point

Reservoir

15

Crystal Reservoir

Blue Mesa Reservoir

92 47

107

61

107°30'

38°30'

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 11. Spatial distribution of median silver concentrations, October 1989 to December 1999.
SURFACE-WATER QUALITY 27

42

109

31 to 57

10 to 30

Median less than 20 (censored)

Median less than 10 (censored)

EXPLANATION

Median zinc concentration,

 in micrograms per liter (μg/L)

 (with site number from Appendix A)

60

Lake City

Ceboll a Creek

Cimarron

Rive r

Henson Cr

53

2

6

7

61

62

9

107°

106°30'

39°

38°30'

107°30'

38°

Blue Mesa Reservoir

Morrow Point

Reservoir

Crystal Reservoir

19

15

28

92

Gunnison

Ohio Creek

48

47

107

45

71

65

Tomich i Creek

Taylor River

Cochetopa Cre ek

Q uartz Creek

23

75

43

44

41

99

98

37

13

83 84

Crested Butte

Slate River

79

78

66 80

40

Pitkin

Taylor Park

 Reservoir

100

104

56

57

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 12. Spatial distribution of median zinc concentrations, October 1989 to December 1999.
28 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Due to changes in standards and improvements 

in constituent minimum reporting levels, only data 

collected since WY 1990 were compared to CDPHE 

standards. Trace-element concentrations exceeded 

standards for six elements: cadmium, copper, lead, 

manganese, silver, and zinc (table 5). Manganese 

concentrations exceeded standards more often than 

any other constituent. Sites near Crested Butte and on 

Henson Creek upstream from Lake City had several 

trace elements in exceedance of CDPHE standards 

(fig. 13).

Temporal Trends

Temporal trend analysis was conducted on 

sites with at least 5 years of data, a period of record 

that ended within the last decade, and had less than 

50 percent of the data censored. If instantaneous 

discharge data were not collected and a site was collocated with a USGS gage, the mean daily streamflow 

was used for flow adjustment. In some cases, the waterquality data record was longer than the streamflow 

record. A trend analysis was conducted without flow 

adjustment over the entire data record, and a second 

analysis was conducted with flow adjustment over the 

period of record that also had streamflow data. Results 

of the trend tests are listed in table 6. A downward trend 

(3 μg/L per year) was identified for dissolved iron 

concentration at the site on the Gunnison River at 

County Road 32 downstream from the city of Gunnison, 

site 47 (fig. 14). Dissolved iron concentrations at this 

site were low; the highest detected concentration was 

120 μg/L, which is below the 300-μg/L CDPHE standard. The cause of this trend was difficult to identify 

due to the lack of data from upstream sites and from 

other tributaries, such as Tomichi Creek. A site on 

the East River downstream from the confluence with 

Cement Creek (site 37) also was evaluated for trend 

in dissolved iron; however, no trend was identified.

Streambed Sediment

Streambed-sediment samples have been collected 

at several locations. In 1977, the USEPA collected 

streambed-sediment samples at five sites near Gunnison 

and south of Blue Mesa Reservoir. The U.S. Forest 

Service collected samples in 1982 and 1991 near 

Sargents and Taylor Reservoir. Samples have been 

collected at 11 sites by the USGS during 1995–99 in the 

Crested Butte and Lake City areas. Results for selected 

trace elements from the 1995–99 samples are compared 

to the Canadian Sediment Quality Guidelines Probable 

Effect Level (PEL) (Canadian Council of Ministers of 

the Environment, 1999) in figure 15. The PEL defines 

the concentration level above which adverse effects 

to aquatic biota are predicted to occur frequently. The 

streambed-sediment results are similar to the watersample trace-element results in that concentrations 

tend to be greater in areas downstream from historical 

mining (Crested Butte and Lake City). Concentrations 

in the lower parts of the basin are less than the Canadian 

PEL’s.

Suspended Sediment

Measured suspended-sediment concentrations 

within the study area were generally low and typical 

of areas in the southern Rocky Mountains. Within 

the upper areas of the watershed, the snowmelt runoff 

periods are generally the only time when sediment 

concentrations are greater than a few milligrams per 

liter. Median concentrations at sites with four or more 

samples during October 1994 to December 1999 are 

shown in figure 16. The Cimarron River below Squaw 

Creek (site 18) in the western area of the basin was 

the only site with a median concentration greater than 

20 mg/L. The higher concentration in this area is probably related to the geology and the more easily erodible soils. Five sites had sufficient data for trend 

analysis of flow-adjusted suspended-sediment concentrations. Trends in suspended-sediment concentration 

were not determined at any site. Results of the trend 

tests are listed below. 

Site name

and number

(Appendix A)

Period

of

record

Flow

adjustmentp-Value

Trend

direction

Suspended

sediment,

median

concentration

(mg/L)

Slate River above 

Oh-Be-Joyful 

Creek, 78

1995–99 Yes 0.19 None 1.5

Slate River above 

Coal Creek, 79

1995–99 Yes 0.24 None 1.5

East River 

below Cement 

Creek, 37

1995–99 Yes 0.21 None 5.0

East River at 

Almont, 41

1995–99 Yes 0.54 None 5.0

Gunnison River 

at County 

Road 32, 47

1995–99 Yes 0.48 None 7.5
SURFACE-WATER QUALITY 29

Table 5. Exceedances of Colorado Department of Public Health and Environment in-stream water-quality standards for 

dissolved trace elements in the upper Gunnison River watershed, October 1989 to December 1999

[No., number; conc., concentration; μg/L, micrograms per liter; <, less than]

Site name and number

(Appendix A)

No. of

samples/

No. of

censored values

Range 

of conc.

(μg/L)

CDPHE

standard

(μg/L)

(chronic/acute)

No. of

samples over

the standards

(chronic/acute)

Cadmium

Oh-Be-Joyful Creek above Slate River near Crested Butte, 66 10/5 <1–1.6 0.47/1.1 5/2

Slate River near Crested Butte, 83 6/5 <1–1.2 0.72/2.0 1/0

Slate River below Crested Butte, 84 58/24 <0.25–1.1 0.72/2.0 2/0

Big Blue in Wilderness Area, 2 5/4 <0.25–2.2 0.60/1.6 1/1

Steuben Creek North of Blue Mesa Reservoir, 92 10/9 <0.25–0.4 0.35/0.72 1/0 

Henson Creek above Lake City, 53 10/3 <0.25–0.97 0.90/0.16 2/7

Copper

Oh-Be-Joyful Creek above Slate River near Crested Butte, 66 10/0 1.9–4.6 4.5/6.2 1/0 

Slate River above Coal Creek, 80 18/17 <4–30 6.7/9.5 1/1

Slate River below Crested Butte, 84 58/54 <4–8 7.2/10.3 1/0

Sc01308603ac00–Rm Biological Laboratory, 32 1/0 184 16/24 1/1

East River below Cement Creek near Crested Butte, 37 25/16 <1–15 13.7/20.9 1/0

Upper Tomichi Creek above Whitepine, 102 4/0 5–11 10.8/16.1 1/0 

Cebolla Creek at USGS gage, 6 6/4 <4–5 4.6/6.2 1/0

Cimarron River below Little Cimarron, 15 10/6 <4–8 7.1/10 1/0

Henson Creek above Lake City, 53 10/8 <4–15 1.1/1.2 2/2

Henson Creek above North Fork Henson, 52 1/0 7 6.2/8.7 1/0

Lead

Oh-Be-Joyful Creek above Slate River near Crested Butte, 66 10/0 3–9.1 8/16 1/0

Slate River below Crested Butte, 84 58/53 <1–5 1.7/38 3/0

Gold Creek above Ohio, 43 9/6 <1–2 1.9/43 1/0 

Cebolla Creek at USGS Gage, 6 6/5 <1–2 0.81/16 1/0

Henson Creek above Lake City, 53 10/1 <1–5 3.0/1.0 1/9

Manganese

Slate River at Highway 135 at Crested Butte, 81 7/0 23–150 50 (chronic) 4 

Slate River near Crested Butte, 83 18/0 15–158 50 (chronic) 9

Slate River below Crested Butte, 84 57/5 13–150 50 (chronic) 30

Slate River above Baxter Gulch at Highway 135 near 

Crested Butte, 85

7/0 46–84 50 (chronic) 4 

Slate River above East River near Crested Butte, 88 6/0 4–70 50 (chronic) 1 

Mill Creek at West Elk Wilderness Trailhead, 65 5/0 12–51 50 (chronic) 1

East River Below Cement Creek near Crested Butte, 37 81/10 <1–54 50 (chronic) 1

Marshall Creek near Sargents, 63 1/0 78 50 (chronic) 1 

Tomichi Creek at Highway 114, 104 8/0 19–62 57 (chronic) 2

Tomichi Creek at Gunnison, 107 21/0 15–90 57 (chronic) 4

Stewart Creek at La Garita Wilderness Area, 95 4/0 28–99 50 (chronic) 2

Cebolla Creek, 9 17/0 9–52 50 (chronic) 1 

Willow Creek West of Lake Fork, 111 1/0 67 50 (chronic) 1

Cimarron Creek below Squaw Creek, 19 18/0 10–100 50 (chronic) 1

Henson Creek above Lake City, 53 10/0 6–97 50 (chronic) 2

Silver

East River at Almont, CO, 41 29/28 <0.2–0.2 0.11/2.9 1/0

Little Cimarron below Firebox Canyon, 20 1/0 0.2 0.01/0.29 1/0
30 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Biology and Other Characteristics

Biological data available for analysis are limited 

and have been published in other reports. Deacon and 

Stephens (1996) summarize historical biological investigations for the Upper Colorado River Basin. Stephens 

and Deacon (1998) present data on fish tissue and 

organic compounds in streambed sediment for the 

Upper Colorado River Basin including three sites 

within the study area. Habitat and fish community 

are discussed for three sites in the study area in Deacon 

and Mize (1997) and Deacon and others (1999). Algal 

biomass in the Slate and East Rivers during winter 

conditions are investigated in Spahr and Deacon (1998). 

Algal and invertebrate data from the East River are 

compared to other sites in the Upper Colorado River 

Basin in Spahr and others (2000). Data for other types 

of water-quality indicators are available for selected 

areas in the basin. Chlorophyll, biochemical oxygen 

demand, and fecal coliform data have been collected 

in the basin and are discussed in the following sections.

Chlorophyll-a

Chlorophyll-a is a measure of the photosynthetic pigments and is used to estimate or indicate 

algal biomass. Data are available for lakes and 

streams in the study area.

Blue Mesa Reservoir Chlorophyll-a

Most of the lake chlorophyll data in the study 

area were collected from Blue Mesa Reservoir by 

the National Park Service. Samples were collected 

at several sites in the reservoir during 1975 and 1983 

to 1985. Four sites in Blue Mesa Reservoir have 

been sampled several times each year for the 1988 

through 1996 period. Concentrations at these four 

sites vary by season and year. Summary statistics 

and results of trend tests for these four Blue Mesa 

Reservoir sites are given below.

Median concentrations were low, and according 

to Likens (1975), values in the 0- to 3-μg/L range 

are typical of oligotrophic lakes (lakes with low 

productivity and supplies of nutrients) and values in 

the 2- to 15-μg/L range are typical of mesotrophic 

lakes (lakes with moderate productivity and supplies 

of nutrients). Reasons for the downward trend at the 

Sunnyside and Iola sites are unknown. The trends are 

not statistically strong (the p-values are close to 0.05), 

and if the 1988 data (which had greater concentrations 

than subsequent years) are removed from the time 

series, these sites no longer show a statistically significant trend. 

Site name

and number

(Appendix A)

Period of

record p-Value Trend

 direction

Chlorophyll-a

minimum,

median, and

maximum

concentration

(μg/L)

Iola, 116 1988–96 0.04 Downward 0.85, 4.92, 16.4

Sunnyside, 117 1988–96 0.03 Downward 1.49, 5.13, 49.1

Haystack 

Gulch, 118

1988–96 0.92 None 0.18, 4.34, 27.3

Lake Fork 

Arm, 126

1988–96 1.0 None 0.21, 3.08, 17.7

Zinc

Slate River above Oh-Be-Joyful Creek near Crested Butte, 78 14/10 <3–61 60/67 1/0 

Slate River near Crested Butte, 83 6/0 31–455 65/72 1/1

Slate River below Crested Butte, 84 57/3 <8–310 65/72 21/17

Sc01308603ac00–Rm Biological Laboratory, 32 1/0 180 141/156 1/1

Gold Creek above Ohio, 43 9/0 9–110 69/77 1/1 

Cebolla Creek at Hot Springs Ranch, 7 11/7 <8–51 40/44 1/1

Cimarron River below Little Cimarron, 15 10/8 <8–160 64/71 1/1

Henson Creek above Lake City, 53 10/0 14–190 110 (acute) 3 (acute)

Table 5. Exceedances of Colorado Department of Public Health and Environment in-stream water-quality standards for 

dissolved trace elements in the upper Gunnison River watershed, October 1989 to December 1999—Continued

[No., number; conc., concentration; μg/L, micrograms per liter; <, less than]

Site name and number

(Appendix A)

No. of

samples/

No. of

censored values

Range 

of conc.

(μg/L)

CDPHE

standard

(μg/L)

(chronic/acute)

No. of

samples over

the standards

(chronic/acute)
SURFACE-WATER QUALITY 31

Mn (95)

Mn (95)

EXPLANATION

Sites with exceedances of CDPHE standards 

 (constituent(s) in exceedance are listed, with site number

 from Appendix A)

Henson Cr

Cd, Cu, Pb, Mn, Zn (53) Cu (52)

Lake City

38°

Cd (2) Ag (20)

Cimarron

Rive r

Cd (92)

Mn (111)

Mn (19)

Cu, Zn (15)

Blue Mesa Reservoir

Morrow Point

Reservoir

Cu, Pb (6)

Crystal Reservoir

107°

106°30'

39°

38°30'

107°30'

Mn (9)

Ceboll a Creek

Zn (7)

Mn (107)

G

Gunnison unnison Rive r

Cochetopa Creek

Tomichi Creek

Q uartz Creek

Ag (41)

Cu (102)

Mn (104)

Mn (63)

Pb, Zn (43)

Pitkin

Cu, Mn (37)

Mn (88)

Mn (85)

Taylor River

Ohio Creek

Crested Butte

Mn (65)

Cu, Zn (32)

Four sites:

Cu (80)

Cd, Cu, Pb, Mn, Zn (84)

Cd, Mn, Zn (83)

Mn (81)

Cd, Cu, Pb (66) 

Zn (78)

Two sites:

Taylor Park

 Reservoir

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 13. Exceedances of Colorado Department of Public Health and Environment in-stream water-quality standards for 

dissolved trace elements, October 1989 to December 1999 (Ag, silver; Cd, cadmium; Cu, copper; Mn, manganese; Pb, 

lead; Zn, zinc).
32 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Table 6. Seasonal Kendall trend-analysis results for selected dissolved trace elements in the upper Gunnison River 

watershed

[No., number; μg/L, micrograms per liter]

Site name and number

(Appendix A)

Period of

record

No. of samples/

No. of censored values

Flow

adjustment p-Value Trend

direction

Median

concentration

(μg/L)

Aluminum

East River below Cement Creek near 

Crested Butte, 37

1995–99 19/8 Yes 1.0 None 11

Cadmium

Slate River below Crested Butte, 84 1994–98 30/12 Yes 0.48 None 0.3

Iron

East River below Cement Creek near 

Crested Butte, 37

1995–99 74/16 Yes 0.69 None 11

Gunnison River at County Road 32 

below the city of Gunnison, 47

1995–99 46/1 Yes 0.01 Downward 28

Manganese

East River below Cement Creek 

near Crested Butte, 37

1995–99 66/6 Yes 0.12 None 5

Slate River below Crested Butte, 84 1990–98 48/0 No 0.44 None 54

Slate River below Crested Butte, 84 1994–98 29/0 Yes 0.76 None 54

Gunnison River at County Road 32 

below the city of Gunnison, 47

1995–99 46/0 Yes 0.26 None 15

Uranium

Indian Creek near Sargents, 56 1979–92 73/1 No 1.0 None 160

Zinc

Slate River below Crested Butte, 84 1988–98 73/7 No 0.75 None 51

Slate River below Crested Butte, 84 1994–98 29/0 Yes 0.26 None 52

120

100

80

60

40

20

0

1995 1996 1997 1998 1999 2000

FLOW-ADJUSTED DISSOLVED IRON, 

IN MICROGRAMS PER LITER

WATER YEAR 

Figure 14. Flow-adjusted dissolved iron concentration at site 47 (Gunnison River at County 

Road 32), October 1995 to December 1999.
SURFACE-WATER QUALITY 33

47

47

Cadmium (3.5)

Copper (197)

Lead (91.3)

Zinc (315)

Arsenic (17)

Less than PEL

Greater than PEL

Element (PEL, micrograms per kilogram)

EXPLANATION

Sampling site and number

 (Appendix A)

Gunnison

Lake City

Morrow Point

Reservoir

Crystal Reservoir

Cochetopa Creek

Ceboll a Creek

Cimarron

Rive r

38°30'

107°30'

38°

50

59

54

Gunnison Rive r

Blue Mesa Reservoir

Tomich i Creek

Q uartz Creek

Crested Butte

Taylor River

East River

Ohio Creek

107°

106°30'

39°

3 sites

 79, 82, 83

Taylor Park

 Reservoir

37

67

78

21

Slate Ri ver

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Pitkin

Figure 15. Spatial distribution of streambed-sediment samples, October 1995 to August 1999, and comparison of 

selected trace-element concentrations to the Canadian Sediment Quality Guidelines Probable Effect Level (PEL).
34 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Gunnison Rive r

83

EXPLANATION

Median suspended-sediment concentration,

 in milligrams per liter (with site number

 from Appendix A)

Less than 10

10 to 20

36

Crested Butte

Gunnison

Lake City

Pitkin

Tomich

Morrow Point Blue Mesa Reservoir i Creek

Reservoir

Crystal Reservoir

Taylor River

Slate River East River Cochetopa Creek

Ceboll a Creek

Q uartz Creek

Ohio Creek

Cimarron

Rive r

107°

106°30'

39°

38°30'

107°30'

38°

Taylor Park

 Reservoir

78

66

79

36

88

37

41

44

71

107

45

47

1

93

10

61

77 30

110

89

74

3

25

29

26

50

64

18

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 16. Spatial distribution of median suspended-sediment concentrations, October 1994 to December 1999.
SURFACE-WATER QUALITY 35

Stream Chlorophyll-a

Samples for stream periphyton chlorophyll-a

have been collected in the Crested Butte, Gunnison, 

and Tomichi Creek areas of the watershed. Data are 

limited with only one to five samples per site from 

December 1996 to September 1998. Figure 17 shows 

the spatial distribution and median concentrations for 

the available data. Concentrations below 3 mg/m2

 are 

typically considered unenriched, and concentrations 

from 3 to 20 mg/m2

 are considered moderately 

enriched (Biggs, 1996). Greater concentrations of 

chlorophyll-a indicate greater algal biomass. The 

abundance of algae increases when nutrient concentrations, light conditions, velocity, and other factors are 

favorable (Porter and others, 1993). Insufficient data 

were available for trend testing or land-use comparisons for periphyton chlorophyll-a.

Biochemical Oxygen Demand

Biochemical oxygen demand (BOD) is a 

measure of the oxygen used during a given period 

(for example, 5 days) for the biochemical degradation 

of organic material plus the oxygen used to oxidize 

inorganic matter. BOD is primarily used as a measure 

of waste loading. The BOD data discussed in this 

section are 5-day BOD concentrations in milligrams 

per liter. The data were collected at several sites during 

the 1970’s and 1980’s by the CDPHE and the USEPA. 

Data for the 1990’s have been collected at 12 sites 

by the USGS in cooperation with local sponsors. 

Concentrations are typically low, and for the 1990’s 

data, range from 0 to 3.2 milligrams per liter (table 2). 

Median concentrations for sites with five or more 

samples during the 1990’s are shown in figure 18. 

Median concentrations in the Crested Butte to 

Gunnison area were less than 2 mg/L. As a point of 

reference, concentrations in a wastewater-dominated 

stream could be in the 10- to 20-milligrams-per-liter 

range or greater. Insufficient biochemical oxygen 

demand data were available for trend testing or landuse comparisons.

Fecal Coliform

Fecal coliforms are those organisms in the 

coliform bacteria group that are present in the feces 

and intestines of warm-blooded animals (Britton and 

Greeson, 1987). Fecal coliforms are considered indicator bacteria for the presence of fecal pollution. 

More than 3,000 fecal coliform samples have been 

collected at 125 sites since 1970. Sixty-seven sites 

had five or more samples during the 1990’s, and the 

spatial distribution of median concentrations for 

these sites is shown in figure 19. With the exception 

of the Cimarron River and Squaw Creek area in the 

western part of the basin, median concentrations of 

fecal coliform were low (less than 100 counts per 

100 milliliters). Sites with low median concentrations 

occasionally had higher concentrations. Table 7 

lists the sites and number of samples that exceed 

200 counts per 100 milliliters. This concentration 

was used for comparison because the CDPHE 

in-stream standard for fecal coliform is 200 counts 

per 100 milliliters based on the geometric mean of 

representative stream samples. Again, with the exception of the Cimarron River and Squaw Creek areas, 

high concentrations were infrequent. Sufficient data 

were available at nine sites to test for trends in fecal 

coliform data. Results of the trend tests are listed 

below. The East River at Almont was the only site 

with a statistically significant trend in fecal coliform 

concentrations. Reasons for the downward trend 

are unknown. Mining and forest classified sites have 

slightly lower median concentrations than sites classified as urban, rangeland, or agriculture. Statistically, 

there were no differences in median concentrations of 

urban, rangeland, or agriculture sites (medians of 9, 

14, and 10 counts per 100 milliliters, respectively). 

Site name

and number

(Appendix A)

Period of

record

Flow

adjustmentp-Value Trend

direction

Fecal

coliform,

median

concentration

(counts per

100 mL)

East River 

below Cement 

Creek, 37

1993–99 No 1.0 None 5

East River at 

Almont, 41

1991–99 No 0.002 Downward 6

 Slate River below 

Crested Butte, 84

1979–98 No 0.4 None 23

Tomichi Creek 

at Gunnison, 107

1991–99 No 0.4 None 45

Iola, 116 1986–96 No 1.0 None 1

Sunnyside, 117 1986–96 No 0.2 None 1

Haystack Gulch, 118 1986–96 No 0.4 None 0

Old Highway 50 

Beach, 120

1986–96 No 0.3 None 1

Cimarron Creek 

below Squaw 

Creek, 19

1986–96 No 0.1 None 105
36 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

41

Crested

 Butte

Gunnison

Lake City

Pitkin

Tomichi Creek

Gunnison Rive r

Blue Mesa Reservoir

Morrow Point

Reservoir

Crystal Reservoir

Taylor River

Slate River East River Cochetopa Creek

Ceboll a Creek

Q uartz Creek

Ohio Creek

Cimarron

Rive r

107°

106°30'

39°

38°30'

107°30'

38°

EXPLANATION

Median chlorophyll-a concentration, in

 milligrams per square meter

 (with site number from Appendix A)

Less than 3

3 to 20

Taylor Park

 Reservoir

106

103

107

39 38

37

36

87,88

35

31

85

83

78, 81 78

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 17. Spatial distribution of median chlorophyll-a concentrations, December 1996 to September 1998.
SURFACE-WATER QUALITY 37

EXPLANATION

Median biochemical oxygen demand,

in milligrams per liter

Median concentration

 and (site number from

 Appendix A)

1.0 (37)

0.7 (36)

0.8 (88)

1.8 (44)

0.9 (47)

1.2 (107)

0.8 (45)

0.6 (70)

0.6 (41)

0.6 (37)

Crested Butte

Gunnison

Lake City

Pitkin

Tomichi Creek

Gunnison Rive r

Morrow Point

Reservoir

Crystal Reservoir

Taylor River

Slate River East River Cochetopa Creek

Ceboll a Creek

Q uartz Creek

Ohio Creek

Cimarron Rive r

107°

106°30'

39°

38°30'

107°30'

38°

Taylor Park

 Reservoir

Blue Mesa Reservoir

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 18. Spatial distribution of median biochemical oxygen demand concentrations, July 1995 to October 1999.
38 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

102

4

EXPLANATION

Median fecal coliform concentration,

 in counts per 100 milliliters

(with site number from Appendix A)

Less than 100

100 to 200

Greater than 200

Crested Butte

Gunnison

Lake City

Pitkin

Tomichi Creek

Gunnison Rive r

Blue Mesa Reservoir

Morrow Point

Reservoir

Crystal Reservoir

Taylor River

Slate River East River Cochetopa Creek

Ceboll a Creek

Q uartz Creek

Ohio Creek

Cimarron

Rive r

107°

106°30'

39°

38°30'

107°30'

38°

Squaw Creek

Taylor Park

 Reservoir

23

57

56

104

43

75

100

107

45

70, 71

44

41, 42 98, 99 65

37

13

88

36

34

33

40

66, 78

79, 80

84, 85

46, 47, 48 114

91

92

116

117

112, 113

119

118, 120

121, 122

109

124

126

127

128

73

7

9

61

62

60

53

28

50

51

19

15

90

16, 17

0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 19. Spatial distribution of median fecal coliform concentrations, October 1989 to December 1999.
GROUND-WATER QUALITY 39

GROUND-WATER QUALITY

Many wells were completed in aquifers 

composed of valley fill and alluvium of Holocene 

age, which included more than 50 percent (55 of 

99 wells) of the total wells and all wells that were 

constructed in the 1990’s. Aquifers composed of 

valley fill and alluvium tend to be relatively shallow 

and unconfined and are located in and near stream 

valleys, primarily near Crested Butte, Lake City, and 

Gunnison (fig. 20). Seventeen wells were completed in 

consolidated sandstone of varying age and are scattered throughout the watershed. Four wells were 

completed in volcanic rocks of varying age and are 

located primarily in the southwestern part of the 

watershed, near Lake City (fig. 20). Seven wells 

were completed in igneous and metamorphic 

rocks of Cambrian age and are located in central and 

northern areas (fig. 20). Well-completion data are 

provided in Appendix B; however, data were not available for 15 wells that were completed during the mid1970’s. Specific sites discussed or shown in figures are 

listed in Appendix B.

Ground-water-quality data were collected by 

the USGS from all 99 wells, 71 of which have historical ground-water-quality data from the mid-1970’s 

and early 1980’s. The water-quality data from the 

remaining 28 wells were collected in 1996 and 1997 as 

part of the USGS National Water-Quality Assessment 

(NAWQA) Program. Many of these wells were 

installed following NAWQA protocols designed to 

limit possible contamination (Lapham and others, 

1995). 

Table 7. Sites and number of samples with fecal coliform concentrations greater than 200 counts per 100 milliliters in the 

upper Gunnison River watershed, October 1989 to December 1999

Site name and number

(Appendix A)

Total number of

samples collected

Range of concentrations

(counts per 100 milliliters)

Number of samples

greater than 200 counts

per 100 milliliters

East River above Crested Butte, 34 30 1–200 1

East River at Almont, 41 48 1–210 1

Slate River near Crested Butte, 83 32 1–340 3

Slate River below Crested Butte, 84 43 1–2,300 5

Slate River above East River, 88 31 1–420 1

Ohio Creek above mouth, 70 6 1–270 1

Ohio Creek above mouth, 71 8 2–250 1

Indian Creek near Sargents, 56 23 3–430 1

Cochetopa Creek above Dome Lakes, 23 6 3–230 1

Tomichi Creek at Gunnison, 107 39 1–230 2

Gunnison River at Riverway, 46 35 0–2,000 2

Steuben Creek north of Blue Mesa, 92 7 0–475 1

Upper North Willow, 113 21 0–3,500 9

Cebolla Creek at USGS gage, 6 4 0–230 1

Cebolla Creek, 9 22 0–255 1

Iola Beach, 114 46 0–3,500 2

Old Highway 50 beach, 120 50 0–1,500 1

Bay of Chickens East, 121 47 0–3,500 5

Bay of Chickens West, 122 48 0–3,500 4

Blue Creek, 4 6 2–207 1

McIntyre Gulch, 127 24 0–345 1

Cimarron Creek above Benney’s, 16 24 0–3,500 11

Cimarron Creek above Squaw Creek, 17 24 0–3,500 11

Cimarron Creek below Squaw Creek, 19 57 0–3,500 22

Squaw Creek above Cimarron Creek, 90 24 0–3,500 16

Crystal Creek, 27 3 60–3,500 1
40 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Qa

Aquifer type near well screen

 (with site number from Appendix B)

Alluvial

Sedimentary

Volcanic

Crystalline

Unknown

Quaternary alluvial and 

unconsolidated material

Tertiary and Late Cretaceous 

 igneous and volcanic rocks

Cretaceous and Jurassic 

sedimentary rocks

Permian and Pennsylvanian 

sedimentary rocks

Cambrian and Precambrian 

igneous and metamorphic rocks

EXPLANATION

Geology

Crested Butte

Gunnison

Lake City

Pitkin

146

143

142

141

140

151

154 153

150 148

149

147

152

145

174

144

138

137 139

136

156 158

159

155

160

169

178 181

215

223

218

216 217

204

195

231

230

234

233

232 228

229

227 224 226

225

221

222

220 219

214

212

209

213 210

211 207

206 208

205

199

203

200

202

201

190

194 197

196 193

198

162 164

163

157

161

166

165 167

168

170

171

173

172

179 180

176

175

177 182

183

184

185

186

187

188 189

192 191

38°30'

107°30'

39°

107°

106°30'

38° 0 5 10 15 20 25 MILES

0 5 10 15 20 25 KILOMETERS

Figure 20. Spatial distribution of wells according to aquifer type, 1970 to 1999.
GROUND-WATER QUALITY 41

Water-quality sampling for field properties 

(water temperature, pH, dissolved oxygen, alkalinity, 

specific conductance, and turbidity) were collected 

at nearly all wells sampled in the 1990’s, whereas 

data from wells sampled before 1990 contained less 

dissolved oxygen, alkalinity, or turbidity data (table 8). 

Major-ion data were collected at nearly all historically 

sampled wells and wells sampled in the mid-1990’s. 

Nutrient (ammonia, nitrate, nitrite, dissolved phosphorus, and orthophosphate) data were collected 

in all wells sampled in the 1990’s, but only nitrate 

and orthophosphate data were available for the historical well-water samples. Trace-element data were 

available for all wells sampled in the 1990’s, but only 

iron and manganese data were consistently available 

for the historical wells.

Field Properties

Physical properties were measured at nearly 

all wells in the 1990’s, and summary statistics are 

presented in table 8. Water temperature ranged 

from 4.3° to 13.8°C, with a median of 10.1°C (table 8). 

Five of the 37 (13 percent) well-water samples had 

dissolved-oxygen concentrations of less than 1 mg/L. 

The range of pH values in the well-water samples 

was 6.2 to 7.8, with a median value of 7.2. Two of 

the 40 samples (at sites located just west of Lake 

City, site 144—Appendix B, and north of Gunnison, 

site 179) had pH values below the USEPA SDWR 

range (6.5 to 8.5) for treated drinking-water 

(U.S. Environmental Protection Agency, 2000).

Major Ions and Dissolved Solids

The following major ions were analyzed in 

ground-water samples from the watershed: bicarbonate, bromide, calcium, chloride, fluoride, magnesium, potassium, silica, sodium, and sulfate (table 8). 

The USEPA has established the SDWR’s for chloride, 

fluoride, and sulfate (table 8). All chloride samples 

met the SDWR of 250 mg/L. All chloride concentrations in ground water were at least one order of magnitude lower than 250 mg/L except for three samples 

collected at site 232, which had concentrations of 100, 

140, and 200 mg/L. The well at this site is located in 

the town of Crested Butte and is constructed in a 

aquifer composed of Holocene-age valley fill and 

alluvium. Elevated chloride concentrations may be 

attributed to anthropogenic activity and may cause 

the drinking water to taste salty if concentrations 

are above 250 mg/L (Apodaca and Bails, 2000). 

The maximum fluoride concentration sampled 

in ground water during the 1990’s was 1.3 mg/L, 

which was below the USEPA SDWR of 2.0 mg/L. 

Four historical fluoride samples, collected from the 

mid-1970’s, exceeded 2.0 mg/L. Two of these wells 

(located east and north of Gunnison, sites 175 and 

187) are completed in sedimentary rocks (Brushy 

Basin Member and Dakota Sandstone). There are no 

well-completion data available for the other two wells 

(located south and east of Gunnison, sites 161 and 

176). No natural or hydrogeologic cause is apparent 

for these elevated concentrations of fluoride. 

All sulfate concentrations, except for one well 

(site 129) with a concentration of 230 mg/L, were 

nearly one order of magnitude smaller than the SDWR 

of 250 mg/L. This well and four historically sampled 

wells (sites 137, 138, 146, and 194) with sulfate 

concentrations exceeding 250 mg/L were completed in 

volcanic-rock aquifers near Lake City. Dissolution and 

oxidation of sulfide minerals in the volcanic-rock 

aquifers may explain the elevated sulfate concentrations in ground water at these locations.

Calcium and magnesium are dominant cations in 

most ground water, and both ions contribute to the hardness of water. Calcium generally is a product of the 

dissolution of carbonate minerals and limestone, 

whereas magnesium is more commonly produced from 

the dissolution of igneous and metamorphic rocks that 

contain ferromagnesian minerals (Hem, 1992). Groundwater samples throughout the watershed tended to have 

higher calcium than magnesium concentrations.

Two of 39 dissolved-solids concentrations in 

ground-water samples exceeded the SDWR of 500 mg/L 

(table 8). These two dissolved-solids concentrations were 

collected from site 232 in Crested Butte. Because all 

dissolved-solids samples collected during the 1990’s 

were from wells constructed in aquifers composed of 

alluvium, a comparison among aquifer types was 

performed on samples collected from 1970 to 1999 

(fig. 21). Due to the small number of ground-water 

samples from wells completed in volcanic and cystalline 

rock, a multiple comparison test of the medians among 

aquifer types was not done. Three of the four dissolvedsolids concentrations from aquifers composed of volcanic 

rock were nearly one order of magnitude greater than 

ground-water samples collected from other aquifer types. 

The volcanic lithology of these aquifers are generally ash 

flow, tuff, and breccia, which tend to dissolve in ground 

water. 
42 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Table 8. Summary of the number of analyses, minimum, median, and maximum concentrations for ground-water-quality 

samples in the upper Gunnison River watershed

[No., number; conc., concentration; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; SDWR, secondary drinking-water regulation; MCL, 

maximum contaminant level; MoE, margin of exposure; NTU, nephelometric turbidity units; pCi/L, picocuries per liter; μg/L, micrograms per liter; <, less 

than; --, not defined]

Constituent or property

(reporting units)

No. of 

analyses/

No. of 

censored

values,

1970–99

No. of 

analyses/

No. of 

censored 

values,

1990–99

No. of

sites,

1990–99

Minimum

value,

1990–99

Median

value,

1990–99

Maximum

value,

1990–99

USEPA

drinkingwater

standards

and health

advisories1

Field properties

Water temperature (degrees Celsius) 109/0 39/0 28 4.3 10.1 13.8 --

Dissolved oxygen (mg/L) 37/2 37/2 27 0.1 2.4 7.3 --

Turbidity (NTU) 35/0 35/0 27 0.09 1.5 58 --

Specific conductance (μS/cm at 

25 degrees Celsius)

111/0 40/0 28 100 331 1,050 --

pH (standard units) 111/0 40/0 28 6.2 7.2 7.8 6.5–8.5 (SDWR)

Alkalinity (mg/L as CaCO3) 42/0 39/0 27 38 133 313 --

Major ions

Bicarbonate, dissolved, field 

(mg/L as HCO3)

10/0 10/0 9 83 168 226 --

Bromide, dissolved (mg/L) 39/14 39/14 27 <0.01 0.016 1.2 --

Calcium, dissolved (mg/L) 106/0 39/0 27 15 53 140 --

Chloride, dissolved (mg/L) 106/0 39/0 27 0.1 1.5 200 250 (SDWR)

Fluoride, dissolved (mg/L) 103/13 39/12 27 <0.1 0.16 1.3 2.0 (SDWR)

Magnesium, dissolved (mg/L) 106/0 39/0 27 1.6 7.8 21 --

Potassium, dissolved (mg/L) 106/0 39/0 27 0.24 1.7 7.4 --

Silica, dissolved (mg/L) 106/0 39/0 27 6.5 13 38 --

Sodium, dissolved (mg/L) 106/0 39/0 27 1.5 4.8 32 --

Sulfate, dissolved (mg/L) 106/0 39/0 27 3.7 17 230 250 (SDWR)

Dissolved solids (mg/L) 39/0 39/0 28 61 195 557 500 (MCL)

Hardness, total (as mg/L of CaCO3) 106/0 39/0 28 44 160 440 --

Nutrients

Ammonia (mg/L as N) 39/25 39/25 27 <0.015 <0.015 0.109 --

Nitrate (mg/L as N) 102/8 39/5 27 <0.05 0.261 4.55 10 (MCL)

Nitrite, dissolved (mg/L as N) 39/39 39/39 27 <0.01 <0.01 <0.01 1 (MCL)

Orthophosphate, dissolved 

(mg/L as P) 

101/23 39/15 27 <0.01 0.014 0.229 --

Phosphorus, dissolved (mg/L as P) 39/22 39/22 27 <0.01 <0.01 0.228 --

Trace elements and radon

Aluminum, dissolved (μg/L) 39/0 39/0 27 3 5.4 10 50–200 (SDWR)

Antimony, dissolved (μg/L) 39/39 39/39 27 <1 <1 <1 6.0 (MCL)

Arsenic, dissolved (μg/L) 61/46 39/32 27 <1 <1 4 10 (MCL)

Barium, dissolved (μg/L) 39/1 39/1 27 <1 73 299 2000 (MCL)

Beryllium, dissolved (μg/L) 39/39 39/39 27 <1 <1 <1 4.0 (MCL)

Boron, dissolved (μg/L) 67/14 28/1 28 6.2 24.5 89 --

Cadmium, dissolved (μg/L) 39/39 39/39 27 <1 <1 <1 5.0 (MCL)

Chromium, dissolved (μg/L) 39/7 39/7 27 <1 2.4 5.3 100 (MCL)

Cobalt, dissolved (μg/L) 39/36 39/36 27 <1 <1 2 --

Copper, dissolved (μg/L) 39/22 39/22 27 <1 <1 127 1,000 (SDWR)

Iron, dissolved (μg/L) 106/20 39/10 27 <3 5.9 7,400 300 (SDWR)

Lead, dissolved (μg/L) 41/38 39/38 27 <1 <1 1.4 --

Manganese, dissolved (μg/L) 105/40 39/12 27 <1 2.1 1,850 50 (SDWR)

Molybdenum, dissolved (μg/L) 39/24 39/24 27 <1 <1 3.7 --

Nickel, dissolved (μg/L) 39/21 39/21 27 <1 <1 3.8 --
GROUND-WATER QUALITY 43

Trace elements and radon—Continued

Selenium, dissolved (μg/L) 61/56 39/38 27 <1 <1 11 50 (MCL)

Uranium, dissolved (μg/L) 39/21 39/21 27 <1 <1 13 30 (MCL)

Zinc, dissolved (μg/L) 39/18 39/18 27 <1 1.4 303 5000 (SDWR)

Radon-222 (pCi/L) 39/0 39/0 426 1,175 3,830 300 (MCL)

Pesticides and volatile organic compounds

Alachlor, dissolved (μg/L) 33/33 33/33 21 <0.002 <0.002 <0.002 2.0 (MCL)

Atrazine, dissolved (μg/L) 33/33 33/33 21 <0.001 <0.001 <0.002 3.0 (MCL)

Bromacil, dissolved (μg/L) 21/20 21/20 9 <0.035 <0.035 0.050 --

Prometon, dissolved (μg/L) 33/32 33/32 21 <0.018 <0.018 0.0365 --

Benzene, total (μg/L) 33/33 33/33 21 <0.032 <0.032 <0.050 5.0 (MCL)

Toluene, total (μg/L) 33/33 33/33 21 <0.038 <0.038 < 0.060 1000(MCL)

Tricholoroethylene, total (μg/L) 33/32 33/32 21 <0.038 <0.038 0.177 5.0 (MCL)

Chloroform, total (μg/L) 33/32 33/32 21 <0.050 <0.052 0.232 80 (MCL)

Methyl tert-butyl ether (μg/L) 33/29 33/29 21 <0.100 <0.112 0.460 20-40 (MoE)

Tetrachloroethylene, total (μg/L) 33/33 33/33 21 <0.038 <0.038 <0.050 5.0 (MCL)

Vinyl chloride, total (μg/L) 33/33 33/33 21 <0.010 <0.112 <0.112 2.0 (MCL)

1,3-Dichlorobenzene (μg/L) 33/32 33/32 21 <0.054 <0.054 0.100 600 (MCL)

1,2,4-Trimethylbenzene, (μg/L) 33/32 33/32 21 <0.050 <0.050 0.328 --

1U.S. Environmental Protection Agency, 2000.

Table 8. Summary of the number of analyses, minimum, median, and maximum concentrations for ground-water-quality 

samples in the upper Gunnison River watershed—Continued

[No., number; conc., concentration; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; SDWR, secondary drinking-water regulation; MCL, 

maximum contaminant level; MoE, margin of exposure; NTU, nephelometric turbidity units; pCi/L, picocuries per liter; μg/L, micrograms per liter; <, less 

than; --, not defined]

Constituent or property

(reporting units)

No. of 

analyses/

No. of 

censored

values,

1970–99

No. of 

analyses/

No. of 

censored 

values,

1990–99

No. of

sites,

1990–99

Minimum

value,

1990–99

Median

value,

1990–99

Maximum

value,

1990–99

USEPA

drinkingwater

standards

and health

advisories1

0

250

500

750

1,000

1,250

1,500

1,750

2,000

 Alluvial Crystalline Sandstone Unknown Volcanic

TOTAL DISSOLVED SOLIDS, 

IN MILLIGRAMS PER LITER

AQUIFER TYPE

EXPLANATION

90

75

50

25

10

Percentiles

(64) 

Data values

 (64) (7) (16) (15) (4) 

Data values outside

the 10th and 90th

percentiles

Number of samples

Figure 21. Distribution of dissolved-solids concentrations by aquifer type for ground-water 

samples, 1970 to 1999.
44 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

Water sampled from similar aquifer types generally has similar water types; 58 of the 63 samples 

collected in alluvial aquifers were calcium bicarbonate 

water type (table 9). Calcium bicarbonate was the dominant water type in nearly all aquifers except for the 

volcanic-rock aquifers, which had more sodium and 

sulfate mixed water types (table 9). Calcium and bicarbonate occur naturally in most ground water and result 

from the dissolution of carbonate minerals such as 

limestone, whereas sodium and sulfate occur more 

commonly from the dissolution of minerals from 

igneous and volcanic rock (Hem, 1992). Although relatively few samples were collected from aquifers of sedimentary rock, the predominant water type was calcium 

bicarbonate because many of the aquifers composed 

of sedimentary rock contain sandy limestone layers.

Nutrients

Elevated concentrations of nutrients, particularly nitrate, can result from the seepage of animal and 

human waste or nitrogen fertilizers into the ground 

water. Wells that can be at risk from elevated nitrate 

concentrations include those constructed in aquifers 

near land-use activities that can result in the seepage or 

leaching of available nitrogen (such as in rangeland, 

urban, and agriculture land uses). Shallow, alluvial 

aquifers associated with these land uses can provide 

the most direct and efficient route for nitrate to enter 

the water-table aquifer. Mueller and Helsel (1996) 

define background levels as having nitrate concentrations less than 2 mg/L.

Table 9. Description of dominant water types of sampled wells in the upper Gunnison River watershed

[Ca, calcium; HCO3, bicarbonate; Cl, chloride; SO4, sulfate; Na, sodium; Mg, magnesium; --, not available]

Geohydrologic description Number of wells

(total 99)

Predominant water type

(number of samples)

Wells completed in alluvium

Cenozoic valley fill 1 --

Holocene flood-plain alluvium 10 Ca - HCO3 (7)

Holocene valley fill 45 Ca - HCO3 (51)

Ca - (HCO3 and Cl mix) (2)

Ca - SO4 (2)

Wells completed in volcanic rock

Tertiary System 1 Na - SO4 (1)

Miocene Series 1 (Ca and Na mixed) - HCO3 (1)

Oligocene Series 2 (Ca and Na mixed) - SO4 (1)

Na - (SO4 and HCO3 mix) (1)

Wells completed in sedimentary rock

Dakota Group, Cretaceous 2 Ca - HCO3 (2)

Dakota Group, Upper Cretaceous 4 Ca - HCO3 (2)

Na - HCO3 (1)

Mancos Shale, Upper Cretaceous 1 Ca - HCO3 (1)

Mesaverde Group, Upper Cretaceous 2 Ca - HCO3 (1)

Burro Canyon Formation, Upper Cretaceous 2 Ca - HCO3 (2)

Morrison Formation, Upper Jurassic Brushy Basin 

Member

4 Ca - HCO3 (3)

(Ca and Na mixed) - HCO3 (1)

Entrada Sandstone, Upper Jurassic 1 Ca - HCO3 (1)

Morrison Formation, Upper Jurassic 1 Ca - HCO3 (1)

Wells completed in crystalline rock

Precambrian Erathem 5 Ca - HCO3 (6)

Precambrian crystalline rock 2 Ca - HCO3 (1)

Wells completed in unidentified lithology

-- 15 Ca - HCO3 (9)

Ca - SO4 (2)

Na - HCO3 (2)

(Ca and Na mixed) - SO4 (1)

(Ca and Na mixed) - HCO3 (1)
GROUND-WATER QUALITY 45

Thirty-nine nutrient analyses were performed on 

water samples from 27 ground-water wells during the 

1990’s (table 8). Nutrient concentrations were generally low. Median concentrations for ammonia, nitrite, 

and dissolved phosphorus were below laboratory 

reporting levels (censored data). 

All nitrate samples were below the USEPA 

drinking-water MCL of 10 mg/L. The highest historical (WY 1970 to 1990) nitrate concentration was 

5.1 mg/L and was detected at a well (site 162) near the 

confluence of Cochetopa Creek and Tomichi Creek in 

WY 1974. The highest nitrate concentration measured 

in the 1990’s was 4.5 mg/L in a well located at Crested 

Butte (site 232).

 Aquifers composed of Holocene-age valley 

fill and alluvium were the only aquifer type to have 

nitrate concentrations exceeding 2 mg/L. The wells 

with nitrate concentrations exceeding 2 mg/L, as well 

as most wells completed in shallow, alluvial aquifers, 

are located in agriculture and urban land-use areas. 

The highest nitrate concentration (5.1 mg/L) was 

measured in 1974 at a well (site 162) in an agriculture 

land-use area. The next four highest nitrate concentrations (4.5, 4.1, 3.8, and 3.7 mg/L) were measured in 

two wells (sites 232 and 173, located in Crested Butte 

and Gunnison, respectively) classified as urban land 

use. The distribution of nitrate concentrations are 

represented on boxplots in figure 22. Differences 

were evaluated using the Kruskal-Wallis test on 

rank-transformed data to determine if median nitrate 

concentrations were significantly different among 

agriculture, forest, rangeland, and urban land-use 

classified wells. The p-value obtained from the 

Kruskal-Wallis test (p-value = 0.46) showed no 

statistical difference between median nitrate concentrations among the four land-use classifications.

Trace Elements and Radon

Summary statistics and USEPA drinking-water 

standards for trace elements and radon are listed in 

table 8. Thirteen of 18 trace elements have USEPAestablished drinking-water standards or regulations; 

for those 13 trace elements, only a few iron and 

manganese concentrations from ground-water samples 

in the watershed exceeded the standards and regulations. Three iron samples exceeded the USEPA SDWR 

of 300 μg/L at two wells (sites 163 and 171) near the 

city of Gunnison and at a well (site 147) south of the 

town of Powderhorn near Cebolla Creek. All three 

wells were completed in aquifers composed of 

Holocene-age valley-fill alluvium. Elevated iron 

concentrations can form red oxyhydroxide precipitates 

that stain laundry and plumbing, creating an objectionable impurity in water supplies (Hem, 1992). Nine of 

39 water samples at six sites (147, 163, 166, 171, 179, 

and 222) analyzed for manganese exceeded the 

USEPA SDWR of 50 μg/L and were collected from 

aquifers composed of Holocene-age valley-fill alluvium near Gunnison, Crested Butte, and in one well 

near Cebolla Creek. Elevated concentrations of 

Agriculture Forest Rangeland Urban

10

1

0.1

0.01

0.001

RL = 0.1

(22) (19) (21) (39)

NITRATE, IN MILLIGRAMS 

PER LITER

LAND USE

Reporting level (RL)

EXPLANATION

90

75

50

25

10

Percentiles

(22) 

Data values outside

the 10th and 90th

percentiles

Number of samples

Figure 22. Distribution of nitrate concentrations by land-use classifications for ground-water 

samples, 1970 to 1999.
46 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

manganese can cause a brown discoloration and affect 

the taste of drinking water and also can deposit blackoxide stains on plumbing and laundry fixtures (Hem, 

1992). Manganese sources are typically associated 

with minerals common to igneous and metamorphic 

rocks (Hem, 1992). No differences were found in 

median concentrations of trace elements for forest, 

rangeland, and urban land uses (Apodaca and Bails, 

2000). Insufficient data were available for comparison 

of other trace-element concentrations and land use. 

Radon gas is a natural radioactive decay product 

of uranium. Sources of radon include soil, rock, mine 

tailings containing uranium, and water that has passed 

through uranium-containing materials. Although still 

under review, the USEPA has established an MCL of 

300 pCi/L for radon in drinking water. The national 

average concentration for radon in ground water was 

350 pCi/L (Paulsen, 1991). All 39 radon samples 

collected at 27 sites (as noted in Appendix B) in the 

watershed exceeded the USEPA MCL and the national 

average. Measured concentrations ranged from 426 to 

3,830 pCi/L (table 8). 

Pesticides and Volatile Organic 

Compounds

Of the 120 pesticide samples summarized 

in table 8, only 2 (bromacil and prometon) had 

concentrations above laboratory reporting limits. 

Neither of the two pesticides have USEPA drinkingwater standards or regulations (table 8). Bromacil 

is a herbicide that controls annual and perennial 

grasses and broadleaf weeds, and prometon is a 

herbicide used as a nonselective soil sterilant in nonagricultural settings. The two pesticides were detected 

in wells located near Gunnison—bromacil at site 179 

and prometon at site 171.

Seven of 21 sites for which ground-water 

samples were analyzed for volatile organic compounds (VOC’s) contained detectable concentrations 

of VOC’s (table 8). The VOC’s detected include 

trichloroethylene (site 221), chloroform (site 229), 

methyl tert-butyl ether (MTBE) (sites 171, 147, 

and 232), 1,3-dichlorobenzene (site 164), and 

1,2, 4-trimethylbenzene (site 222). All detected 

VOC concentrations were below USEPA drinkingwater standards. These VOC’s have a varied use and 

source; trichloroethylene is a metal degreaser; MTBE 

is added to gasoline to increase the octane and reduce 

carbon monoxide emissions; 1,3-dichlorobenzene is 

common in insecticides and other fumigants; and 

1,2,4-trimethylbenzene is a petroleum by-product. 

The wells with VOC detections are located near 

Gunnison and Crested Butte. A well located in 

Crested Butte (site 232) had four detections of MTBE, 

which was the most frequently detected VOC in the 

watershed.

SUMMARY

The retrospective water-quality analysis for the 

upper Gunnison River watershed was limited to waterquality data in an electronic (computerized database) 

format and included only samples gathered from 

October 1969 to December 1999. Data were obtained 

from the USGS National Water Information System 

(NWIS) and the USEPA Storage and Retrieval 

(STORET) databases. For selected water-quality 

constituents in the watershed, this report presents a 

data summary, temporal trend analysis, spatial distribution evaluation, comparison to State and Federal 

standards, and an analysis of the relation between 

land-use practices and water quality.

Surface-water-quality data were collected and 

compiled at 482 sites in the upper Gunnison River 

watershed. Field properties (temperature, dissolved 

oxygen, pH, and specific conductance) were collected 

at nearly all surface-water sites. Major ions, nutrients, 

and trace elements also were commonly collected. 

Most values of surface-water temperature, 

dissolved oxygen, and pH were within CDPHE 

in-stream standard ranges. Only 11 samples had 

water temperatures exceeding the CDPHE in-stream 

standard of 20°C. These measurements were made 

during summer periods at two sites on Tomichi Creek 

and one site on Cochetopa Creek. During the 1990’s, 

no site in the watershed had a median dissolvedoxygen concentration below the minimum CDPHE 

standard of 6 mg/L. Few pH values were outside 

the range defined by CDPHE in-stream standards 

(6.5 to 9.0); three pH values were more acidic and 

only two values were more basic than the standards. 

No temporal trends in pH were identified. 

Calcium-bicarbonate type water was the most 

spatially dominant from July to April (nonspringtime 

runoff conditions) and was present in nearly all 
SUMMARY 47

reaches of the watershed. Calcium-sulfate type water 

is present in Henson Creek and the Lake Fork of the 

Gunnison River, upstream from Lake City, and is 

attributed to the weathering of sulfate-bearing rocks 

associated with historical mining. Total chloride 

concentrations were well below in-stream standards; 

only one total sulfate concentration (260 mg/L) 

exceeded the in-stream standard and was measured 

at Indian Creek near Sargents.

Most sites sampled for nutrients were 

along the Slate River and East River near Crested 

Butte and along the Gunnison River from the confluence of the East and Taylor Rivers to the western 

edge of the watershed. Median ammonia concentrations were relatively low, and many of the sampling 

sites had more than 50 percent censored data. All 

computed un-ionized ammonia concentrations were 

below the chronic standard of 0.02 mg/L, and the 

maximum concentration was an order of magnitude 

below the standard. Of the sites having less than 

50 percent censored nitrate concentration data, three 

sites had median concentrations (0.44, 0.25, and 

0.24 mg/L) greater than 0.21 mg/L. All nitrate concentrations were below the CDPHE in-stream standard 

of 10 mg/L. More than 30 percent of stream sites in 

the watershed (23 of 61 sites) had median total phosphorus concentrations greater than the USEPA recommendations for controlling eutrophication. These sites 

are located on the Cimarron River and tributaries 

(5 sites); tributaries to Blue Mesa, Morrow Point, 

Crystal Reservoirs (13 sites); the Gunnison River 

downstream from Gunnison (3 sites); Mill Creek 

(tributary to Ohio Creek, 1 site); and Cochetopa 

Creek (1 site).

 Temporal trends were not identified for 

either nitrate or total phosphorus. However, at the 

Slate River near Crested Butte site, ammonia concentrations had a statistically significant (alpha level of 

0.05) upward trend, with a p-value of 0.016. The Slate 

River near Crested Butte site is located immediately 

downstream from the towns of Crested Butte and 

Mount Crested Butte and may reflect recent population growth or other land-use changes in the area. The 

rate of change of the trend is small (0.017 mg/L/year). 

Un-ionized ammonia concentrations at this site were 

relatively low and well below CDPHE in-stream standards, presenting no apparent environmental concern 

from the un-ionized species of ammonia.

Although the multiple comparison test showed 

nitrate concentrations were statistically different 

between agriculture and forest and between agriculture 

and urban land-use classified sites, median concentrations were low among all land-use settings and most 

concentrations were less than national background 

levels (0.6 mg/L). Median concentrations of total 

phosphorus were greatest in rangeland areas and least 

in the urban areas. No significant differences were 

identified for median concentrations of total phosphorus in agricultural and forested areas.

Most trace-element samples were collected on 

the Slate, East, and Gunnison Rivers from Crested 

Butte to the city of Gunnison. Median concentrations 

of arsenic, lead, mercury, selenium, and silver were 

low or censored throughout the watershed. Aluminum, 

cadmium, copper, lead, manganese, and zinc had 

elevated concentrations near Crested Butte and on 

Henson Creek upstream from Lake City. These were 

the only two areas in which elevated trace-element 

concentrations were consistently detected, and both 

are downstream from historical mining areas. Samples 

exceeded standards for six trace elements: cadmium, 

copper, lead, manganese, silver, and zinc. Manganese 

concentrations exceeded standards more often than 

any other trace element. Sites near Crested Butte 

and on Henson Creek upstream from Lake City had 

several trace-element concentrations in exceedance 

of CDPHE standards. A downward trend (3 μg/L per 

year) was identified for dissolved iron concentration in 

samples from a site on the Gunnison River at County 

Road 32 below the city of Gunnison. Dissolved iron 

concentrations at this site were low; the highest 

detected concentration was 120 μg/L, which is 

below the 300-μg/L CDPHE standard. Trace elements 

in bed sediment had spatial distributions similar to 

trace elements in water, and the greater concentrations 

were measured in samples from historical mining 

areas near Lake City and Crested Butte. Concentrations of selected trace elements exceeded the Canadian 

Probable Effect Levels in the historical mining areas. 

Suspended-sediment concentrations were generally 

low (less than 20 mg/L), and no temporal trends 

were detected.

Biological data available for analysis are 

limited. Chlorophyll-a concentrations in samples from 

Blue Mesa Reservoir and streams in the Crested Butte 

and Gunnison areas were typical of unenriched to 

moderately enriched conditions. Biochemical oxygen 
48 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

demand was typically low, with median concentrations 

in the Crested Butte to Gunnison area of less than 

2 mg/L. Occasional high concentrations of fecal 

coliform occur in the watershed. However, with the 

exception of the Squaw Creek and Cimarron River 

area, median concentrations were less than 100 counts 

per 100 milliliters.

Ground-water-quality data were collected by the 

USGS from 99 wells. Water-quality samples for physical properties, major ions, nutrients, and trace 

elements were collected at nearly all wells sampled 

during the 1990’s. Many wells were completed in 

aquifers composed of Holocene-age alluvium and 

valley fill, which include more than one-half (56 of 

99 wells) of the total wells and all wells that were 

constructed in the 1990’s. 

Most field properties were within the USEPA 

SDWR range for treated drinking water. Calcium 

bicarbonate was the dominant water type in samples 

from nearly all wells except for samples from wells 

completed in volcanic rock, which had more sodium 

and sulfate mixed water types. All ground-water 

samples were lower than the SDWR for chloride. 

The three greatest concentrations of chloride were 

collected at site 232. This well is supplied by an 

aquifer composed of Holocene-age valley fill and 

alluvium and is located in the town of Crested Butte. 

Elevated chloride concentrations may be attributed to 

anthropogenic activity and may cause the drinking 

water to taste salty. Wells with sulfate concentrations 

exceeding the SDWR of 250 mg/L were completed in 

aquifers of volcanic rock near Lake City. Dissolution 

and oxidation of sulfide minerals in the aquifers 

composed of volcanic rock may explain the elevated 

sulfate concentrations in ground water at these locations. Dissolved-solids samples from 2 of 39 samples 

exceeded the SDWR of 500 mg/L. These samples 

were from site 232 in Crested Butte.

Thirty-nine nutrient analyses were performed 

on water samples from 27 wells during the 1990’s. 

Nutrient concentrations were generally low, and 

median concentrations for ammonia, nitrite, and 

dissolved phosphorus were below censoring levels. All 

nitrate samples were below the USEPA drinking-water 

MCL of 10 mg/L. Wells most at risk from elevated 

nitrate concentrations can include those constructed 

in aquifers near land-use activities that result in the 

seepage of animal and human waste (such as in rangeland, urban, and agriculture land uses). Shallow, 

alluvial aquifers associated with these land uses can 

provide the most direct and efficient route for nitrate to 

enter the water-table aquifer. However, there were no 

statistical differences between nitrate concentrations 

from wells in agriculture, forest, rangeland, or urban 

land-use settings.

Trace elements in ground water were 

generally below the USEPA SDWR. Three iron 

samples exceeded the USEPA SDWR of 300 μg/L 

at two wells near Gunnison and at a well south of the 

town of Powderhorn near the Cebolla River. Nine of 

39 manganese samples exceeded the USEPA SDWR 

of 50 μg/L; these samples were collected from aquifers composed of valley fill and alluvium of Holocene 

age near Gunnison and Crested Butte and in one well 

near the Cebolla River. All 39 radon samples collected 

from ground water in the watershed exceeded the 

proposed USEPA drinking-water standard (300 pCi/L 

MCL) and ranged from 426 to 3,830 pCi/L. 

Only 2 of 120 pesticide samples (bromacil 

and prometon) had concentrations above censoring 

limits. Five of 21 sites for which ground-water 

samples were collected and analyzed for volatile 

organic compounds (VOC’s) contained detectable 

concentrations. The VOC’s detected include trichloroethylene, chloroform, methyl tert-butyl ether (MTBE), 

1,3-dichlorobenzene, and 1,2,4-trimethylbenzene. All 

detected VOC concentrations met USEPA drinkingwater standards.

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Apodaca, L.E., and Bails, J.B., 2000, Water quality in 

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Water-Resources Investigations Report 99–4222, 

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and habitat on composition of fish communities in the 

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to stream water quality and environmental setting 

in the Upper Colorado River Basin, 1938–95: U.S. 

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and Hallam, C.A., 1983, U.S. Geological Survey 

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land cover digital data: U.S. Geological Survey 

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Community information—Economic base 

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in water resources: New York, Elsevier Science 

Publishers B.V., 529 p.

Hem, J.D., 1992, Study and interpretation of the chemical 

characteristics of natural waters: U.S. Geological 

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population data to indicate new residential development: U.S. Geological Survey Water-Resources Investigations Report 94–4250, 15 p.

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basic science of poisons: New York, McGraw-Hill, 

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and Ruddy, B.C., 1995, Nutrients in ground water 

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Area—Quick facts (accessed 07/26/01 on the World 

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rock, and soil, and indoor air of the Northeastern 

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review and summary of data, in Gunderson, L.C.S., 

and Wanty, R.B., eds., Field studies of radon in 

rocks, soils, and water: U.S. Geological Survey 

Bulletin 1971, p. 195–255.

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50 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

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N.J., Smith, C.M., and Driver, N.E., 2000, Water quality 

in the Upper Colorado River Basin, Colorado, 1996–98: 

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the winter recreational season, December 1996: U.S. 

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APPENDIXES
A

PPENDIXA53

Appendix A. Selected surface-water sites in the upper Gunnison River Basin[NWIS, National Water Information System; STORET, Storage and retrieval database; CDPHE, Colorado Department of Public Health and Environment; NPS, National SP, spring; LK, lake; UNLV, University of Nevada–Las Vegas Toxic Metals in Water data]

Site number for 

this report

Information from USGS NWIS or USEPA STORET

Site number as appears

in database

Site names as they appear

 in database Latitude Longitude

1 382943107015300 Beaver Creek at Beaver Creek Picnic Area 382943 1070153 2 10238 Big Blue in Wilderness Area 381243 1072312 3 382418107242600 Blue Creek at Hwy 50 382418 1072426 4 CURE_BC01 Blue Creek 382509.7 1072424.8 5 09113100 Castle Creek above Mouth near Baldwin, Co 384610 1070500 6 10282 Cebolla Cr. @ Usgs Gage 381339 1070422 7 10281 Cebolla Cr. @ Hot Springs Ranch 381339.5 1070422 8 381626107055400 Cebolla Hot Springs 'A' 381626 1070554 9 CURE_CB1A Cebolla Creek 381632.3 1070546.7 

10 381633107054700 Cebolla Creek at Bridge SE Of Powderhorn 381633 1070547 11 385006106493400 Cement Creek Warm Spring 385006 1064934 12 384857106522800 Ranger Warm Spring 384857 1065228 13 10121 Approx. 1/3 Mi. above Campground. 384943 1064945 14 09126000 Cimarron River near Cimarron, Co. 381525 1073245 15 10230 Cimarron River blw. Little Cimarron 382600 1073234 16 CURE_CM12 Cimarron Ck above Benny's 382611.6 1073251 17 CURE_CM08 Cimarron Ck above Squaw Ck 382627.5 1073314.4 18 09127000 Cimarron River bl Squaw Creek, Nr Cimarron, Co. 382647 1073318 19 CURE_CM10 Cimarron Ck below Squaw Ck 382653.6 1073312.2 20 10237 Little Cimmarron blw Firebox Canyon 381328 1072804 21 09111000 Coal Creek near Crested Butte, Co. 385123 1070319 22 03032231 Crested Butte Colorado Slate R.Coal Cr.Gunnison 385220 1070020 23 10325 Cochetopa Cr. above Dome Lakes 381816.2 1064449.2 24 09118450 Cochetopa Creek below Rock Creek Nr Parlin, Co. 382008 1064618 25 382730107232900 Corral Creek at Hwy 92 382730 1072329 26 383150107333300 Crystal Creek at Hwy 92 383150 1073333 27 CURE_CYC1 Crystal Creek 382946.6 1073503.8 28 CURE_CUR2 Curecanti Creek 382715.7 1072506.2 29 09125000 Curecanti Creek near Sapinero, Co. 382916 1072452 30 382900107101600 East Elk Creek at Campground abv Blue Mesa Res 382900 1071016 
54 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99 31 385741106592900 East River above Gothic 385741 1065929 

32 385726106591600 Sc01308603ac00–Rm Biological Laboratory 385700 1065910 33 385609106575800 East River below Gothic 385609 1065758 34 385408106543600 East River above Crested Butte 385408 1065436 35 09110500 East River near Crested Butte, Co. 385152 1065433 36 384950106544200 East River above Slate River Nr Crested Butte 384950 1065442 37 09112200 East River bl Cement Creek Nr Crested Butte, Co. 384703 1065213 38 384557106515000 East River Ditch Number 1 at Highway 135 384557 1065150 39 384541106513100 East River Ditch Number 1 near Spann Ranch 384541 1065131 40 10118 East R. above Gothic 384506 1065922 41 09112500 East River at Almont Co. 383952 1065051 42 000078 East River at Confl. With Taylor 383952 1065051 43 10336 Gold Cr. above Ohio 383455 1065031 44 383838106515400 Gunnison River below Almont 383838 1065154 45 09114500 Gunnison River near Gunnison, Co. 383231 1065657 46 CURE_GR07 Gunnison River - Riverway 383113.2 1065940.6 47 383103106594200 Gunnison River at Cnty Rd 32 below Gunnison, Co 383103 1065942 48 000057 Gunnison River West Of Gunnison 383100 1070000 49 CURE_GR4A Gunnison River - Cooper Ranch 382958.2 1070129.3 50 09128000 Gunnison River below Gunnison Tunnel, Co. 383145 1073854 51 CURE_GR01 Gunnison River - Black Canyon 383132.1 1073855 52 HC2 Henson Creek abv North Fork Henson 380022 1072706 53 10246 Henson Cr. above Lake City 380113 1071953 54 380133107190000 Hensen C at Mouth at Lake City, Co 380133 1071900 55 NHC1 North Fork Henson Creek 380027 1072800 56 000149 Indian Creek near Sargents 382832 1062127 57 10392 Indian Cr. @ Mouth 382234 1062134 58 09123400 Lake Fork below Mill Gulch near Lake City, Co. 375423 1072303 59 375655107180400 Lakefork Gunnison abv Lake San Cristobal at 7 Rd 375655 1071804 60 10248 Lake Fk. Gunnison River above Lake San Cristobal 375659 1071806 

Appendix A. Selected surface-water sites in the upper Gunnison River Basin—Continued

[NWIS, National Water Information System; STORET, Storage and retrieval database; CDPHE, Colorado Department of Public Health and Environment; NPS, National SP, spring; LK, lake; UNLV, University of Nevada–Las Vegas Toxic Metals in Water data]

Site number for 

this report

Information from USGS NWIS or USEPA STORET

Site number as appears

in database

Site names as they appear

 in database Latitude Longitude
APPENDIX A 55

61 09124500 Lake Fork at Gateview, Co. 381756 1071346 62 CURE_LF01 Lake Fork 381927.3 1071336.5 63 10390 Marshall Cr. Nr. Sargents 382117.4 1064053.6 64 382720107324000 Mesa Creek at Footbridge abv Crystal Reservoir 382720 1073240 65 10267 Mill Cr. @ West Elk Wilderness Trailhead 384143 1070341 66 385426107013400 Oh-Be-Joyfull Cr Ab Slate River Nr Crested Butte 385426 1070134 67 385437107015600 Oh-Be-Joyful C at Mo Nr Crested Butte, Co. 385437 1070156 68 09113300 Ohio Creek at Baldwin, Co. 384556 1070328 69 09113500 Ohio Creek near Baldwin, Co. 384208 1065952 70 09113980 Ohio Creek above Mouth, Nr. Gunnison, CO 383516 1065551 71 383516106555000 Ohio Creek above Mouth, near Gunnison, Co 383515 1065550 72 PALMETTO3 Palmetto Gl blw Hough Mine 375833 1073447 73 CURE_PC01 Pine Creek 382649 1072039.8 74 382702107203900 Pine Creek above Morrow Point Reservoir 382702 1072039 75 10335 Quartz Cr. below Ohio City 383355 1065031 76 09118000 Quartz Creek near Ohio City, Co. 383335 1063809 77 382902107140400 Red Creek above blue Mesa Reservoir 382902 1071404 78 385429107013000 Slate Ri Ab Oh-Be-Joyfull Cr Nr Crested Butte 385429 1070130 79 385240106583600 Slate Ri above Coal Cr near Crested Butte 385240 1065836 80 000150 Slate River above Coal Creek 385238 1065836 81 385237106583300 Slate River at Hwy 135 at Crested Butte, Co. 385237 1065833 82 385231106583200 Slate R bl Coal C at Crested Butte, Co. 385231 1065832 83 09111500 Slate River near Crested Butte, Co. 385210 1065810 84 000151 Slate R. blw Crested Butte 384049.8 1065630.6 85 385106106571000 Slate R Ab Baxter Gl @Hwy 135 Nr Crested Butte 385106 1065710 86 03038221 Crested Butte Colorado,Slate R.Coal Cr.Gunnison 385010 1065610 87 384853106541500 Slate R at Mouth Nr Crested Butte, Co. 384853 1065415 88 384852106541500 Slate River above East River near Crested Butte 384852 1065415 89 383137107183600 Soap Creek at Ponderosa Campground abv Blue Mesa 383137 1071836 90 CURE_SC09 Squaw Ck above Cimarron Ck 382631.5 1073328.1 

Appendix A. Selected surface-water sites in the upper Gunnison River Basin—Continued

[NWIS, National Water Information System; STORET, Storage and retrieval database; CDPHE, Colorado Department of Public Health and Environment; NPS, National SP, spring; LK, lake; UNLV, University of Nevada–Las Vegas Toxic Metals in Water data]

Site number for 

this report

Information from USGS NWIS or USEPA STORET

Site number as appears

in database

Site names as they appear

 in database Latitude Longitude
56 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99 91 CURE_STC1 Steuben Creek 382935.6 1070335.3 

92 10255 Steuben Cr. North Of Blue Mesa Res. 383011 1070341 93 382937107033500 Steuben Creek above Blue Mesa Reservoir 382937 1070335 94 CURE_SC01 Steuben Creek - Access Road 382936.3 1070335.5 95 10329 Stewart Cr. @ La Garita W.A. 380126 1065031 96 09107000 Taylor River at Taylor Park, Co. 385059 1063421 97 09109000 Taylor River below Taylor Park Reservoir, Co. 384906 1063631 98 000058 Taylor River at Almont 383952 1065041 99 09110000 Taylor River at Almont, Co. 383952 1065041 

100 10160 Texas Cr. @ Mouth 385048 1063325 101 09107500 Texas Creek at Taylor Park, Co. 385041 1063412 102 10309 Upper Tomichi Cr. above Whitepine 383256 1062329 103 09115500 Tomichi Creek at Sargents, Co. 382442 1062520 104 10301 Tomichi Cr. @ Hwy 114 382606 1063355 105 09117000 Tomichi Creek at Parlin, Co. 382950 1064332 106 383126106475600 Tomichi Ck. blw. Cochetopa Ck. Nr. Parlin, Co 383126 1064756 107 09119000 Tomichi Creek at Gunnison, Co. 383118 1065625 108 383050106302700 Waunita Hot Spring C 383050 1063027 109 CURE_WEC1 West Elk Creek 383021.3 1071622.1 110 383028107162200 West Elk Creek above Blue Mesa Reservoir 383028 1071622 111 10235 Willow Cr. West Of Lake Fork 382230 1071800 112 CURE_NW06 Lower North Willow 382857.8 1070657.2 113 CURE_NW11 Upper North Willow 382906.4 1070712 114 CURE_BM17 Iola Beach 382851.3 1070344.6 115 382856107050000 Blue Mesa Reservoir at Iola Basin 382856 1070500 116 CURE_BM05 Iola 382824.6 1070535.9 117 CURE_BM04 Sunnyside 382903.4 1070600.4 118 CURE_BM03 Haystack Gulch 382755.2 1070940.3 119 CURE_BM19 Elk Creek Marina 382739 1070952.2 120 CURE_BM14 Old Hwy 50 Beach 382806.5 1071034.7 

Appendix A. Selected surface-water sites in the upper Gunnison River Basin—Continued

[NWIS, National Water Information System; STORET, Storage and retrieval database; CDPHE, Colorado Department of Public Health and Environment; NPS, National SP, spring; LK, lake; UNLV, University of Nevada–Las Vegas Toxic Metals in Water data]

Site number for 

this report

Information from USGS NWIS or USEPA STORET

Site number as appears

in database

Site names as they appear

 in database Latitude Longitude
APPENDIX A 57

121 CURE_BM16 Bay Of Chickens East 382835.9 1071036.8 122 CURE_BM15 Bay Of Chickens West 382832.7 1071048.7 123 382829107122200 Blue Mesa Reservoir at Cebolla Basin 382829 1071222 124 CURE_BM18 Blue Mesa Highlands 382817.3 1071715 125 382831107172600 Blue Mesa Reservoir at Sapinero Basin 382831 1071726 126 CURE_BM01 Lake Fork Arm 382645.3 1071753.2 127 CURE_BM13 Mcintyre Gulch 382824.9 1071834.6 128 CURE_BM02 Lake Fork Marina 382728 1071921.4 129 CURE_CL04 Crystal Reservoir 382718.4 1073241.6 130 382710107323000 Crystal Reservoir blw Morrow Point Dam Powerhous 382710 1073230 131 383024107371800 Crystal Reservoir near Crystal Dam 383024 1073718 132 382711107201200 Morrow Point Res blw Blue Mesa Dam Powerhouse 382711 1072012 133 CURE_MPL6 Morrow Point Reservoir 382707.8 1072043.8 134 382644107271000 Morrow Point Reservoir at Kokanee Bay 382644 1072710 135 382702107315400 Morrow Point Reservoir near Dam Of 382702 1073154 

Appendix A. Selected surface-water sites in the upper Gunnison River Basin—Continued

[NWIS, National Water Information System; STORET, Storage and retrieval database; CDPHE, Colorado Department of Public Health and Environment; NPS, National SP, spring; LK, lake; UNLV, University of Nevada–Las Vegas Toxic Metals in Water data]

Site number for 

this report

Information from USGS NWIS or USEPA STORET

Site number as appears

in database

Site names as they appear

 in database Latitude Longitude
APPENDIX B 59

Appendix B. Characteristics of ground-water-quality sites in the upper Gunnison River watershed, 1970–99

[FP, field properties; MI, major ions; TE, trace elements; N, nutrients; R, radon]

Site number

for this report

Site

identification

Sample

date(s)

Depth

to water

(feet)

Approximate age and

lithologic unit near well screen

Type of

data

136 375523107194601 05/16/1974 -- Holocene valley-fill sand FP, MI,TE, N

137 375900107174001 09/23/1981 -- Tertiary System FP, MI,TE

138 375910107174001 09/23/1981 -- Oligocene Series FP, MI,TE

139 375920107173000 08/27/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

140 380018107182401 05/16/1974 -- -- FP, MI,TE, N

141 380032107180600 08/05/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

142 380213107183201 05/15/1974 -- Holocene valley-fill sand FP, MI,TE, N

143 380244107181700 08/27/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

144 380307107181400 08/27/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

145 380314107043401 05/16/1974 -- Holocene valley-fill sand FP, MI,TE, N

146 380435107175001 09/23/1981 -- Oligocene Series FP, MI,TE

147 381339107042500 09/18/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

148 381620107051801 05/15/1974 -- Precambrian erathem FP, MI,TE, N

149 381634107054701 05/15/1974 -- Upper Cretaceous Dakota Sandstone FP, MI,TE, N

150 381700107141401 05/15/1974 -- Miocene Series FP, MI,TE, N

151 381709107325801 05/27/1974 -- Holocene valley-fill sand FP, MI,TE, N

152 381804107061000 09/17/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

153 381824107113200 09/15/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

154 382240107295501 05/27/1974 -- Holocene valley-fill sand FP, MI,TE, N

155 382414106244900 08/04/1997 -- Holocene valley-fill alluvium FP, MI,TE, N, R

156 382741107095901 05/28/1974 -- Precambrian metamorphic rock FP, MI,TE, N

157 382758106563701 06/11/1974 -- Holocene alluvium FP, MI,TE, N

158 382802107055001 05/28/1974 -- -- FP, MI,TE, N

159 382942106434101 06/08/1974 -- Precambrian crystalline rocks FP, MI,TE, N

160 382954106425401 06/10/1974 -- Precambrian metamorphic rock FP, MI,TE, N

161 382954106555401 06/12/1974 -- -- FP, MI,TE, N

162 383005106461801 06/10/1974 3.0 Holocene valley-fill sand FP, MI, TE, N

163 383109106573400 08/05/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

164 383121106583000 08/28/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

165 383129106480001 07/27/1976 26.0 -- FP, MI, TE, N

166 383130106574100 05/08/1997

10/09/1997

10.58

6.5

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

167 383150106565501 06/11/1974 2 Holocene valley-fill sand FP, MI, TE, N

168 383150106574601 06/11/1974 -- Upper Jurassic Brushy Basin Shale 

Member of Morrison Formation 

FP, MI, TE, N

169 383159106395001 06/10/1974 -- Upper Jurassic Brushy Basin Shale 

Member of Morrison Formation

FP, MI, TE, N

170 383203106570101 08/28/1976 -- Holocene alluvium FP, MI, TE, N

171 383219106565300 05/08/1997

10/09/1997

3.0

3.0

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

172 383232106550500 12/04/1996

05/07/1997

10/10/1997

17.7

19.85

15.9

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

FP, MI, TE, N, R
60 Water-Quality Data Analysis of the Upper Gunnison River Watershed, Colorado, 1989–99

173 383232106554700 05/06/1997

10/09/1997

19.1

8.6

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

174 383236106513100 08/25/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

175 383242106515201 06/10/1974 -- Upper Jurassic Brushy Basin Shale 

Member of Morrison Formation

FP, MI, TE, N

176 383258106531501 06/13/1974 33.0 -- FP, MI, TE, N

177 383304106571001 06/12/1974 -- Lower Cretaceous Burro Canyon 

Formation

FP, MI, TE, N

178 383326106373900 08/06/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

179 383334106555400 12/03/1996

05/29/1997

10/08/1997

13.3

4.06

10.4

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

FP, MI, TE, N, R

180 383404106550601 08/24/1977 7.0 Cretaceous Dakota Sandstone FP, MI, TE

181 383412106363401 06/08/1974 -- Holocene valley-fill sand FP, MI, TE, N

182 383431106540301 02/12/1977 239 -- FP, MI, TE, N

183 383436106540701 08/19/1977 113 Cretaceous Dakota Sandstone FP, MI, TE, N

184 383440106551501 08/26/1976 12 Holocene alluvium FP, MI, TE, N

185 383518106553601 10/14/1976 15 -- FP, MI, TE, N

186 383522106553101 10/14/1976 157 Upper Cretaceous Dakota Sandstone FP, MI, TE, N

187 383543106563201 10/29/1976 178 Upper Cretaceous Dakota Sandstone FP, MI, TE, N

188 383549106561201 10/14/1976 32 -- FP, MI, TE, N

189 383555106552801 06/13/1974 -- Holocene valley-fill sand FP, MI, TE, N

190 383623106525601 06/11/1974 3.0 Holocene valley-fill sand FP, MI, TE, N

191 383642106304601 06/08/1974 -- Holocene valley-fill sand FP, MI, TE, N

192 383657106305601 06/08/1974 -- -- FP, MI, TE, N

193 383754106522401 08/17/1977 33 Lower Cretaceous Burro Canyon 

Formation

FP, MI, TE, N

194 383800106523201 08/17/1977 134 -- FP, MI, TE, N

195 383817106562801 06/10/1974 -- Holocene valley-fill sand FP, MI, TE, N

196 383827106515801 05/17/1974 -- Holocene valley-fill sand FP, MI, TE, N

197 383849106515201 08/26/1976 -- Upper Jurassic Morrison Formation FP, MI, TE, N

198 383852106515601 08/27/1976 -- Upper Cretaceous Dakota Group FP, MI, TE, N

199 383953106502601 08/27/1976 21.0 Precambrian crystalline rocks FP, MI, TE, N

200 383953106503000 08/07/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

201 384003106504401 08/26/1976 -- Holocene alluvium FP, MI, TE

202 384014106511201 06/07/1974 -- Upper Jurassic Brushy Basin Shale 

Member of Morrison Formation

FP, MI, TE, N

203 384050106511500 08/07/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

204 384126106590200 08/26/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

205 384130106492201 05/17/1974 -- Holocene valley-fill gravel FP, MI, TE, N

206 384250106511501 08/23/1977 -- -- FP, MI, TE, N

207 384255106510801 10/28/1976 14.0 Holocene alluvium FP, MI, TE, N

208 384258106504601 06/07/1974 -- -- FP, MI, TE, N

Appendix B. Characteristics of ground-water-quality sites in the upper Gunnison River watershed, 1970–99—Continued

[FP, field properties; MI, major ions; TE, trace elements; N, nutrients; R, radon]

Site number

for this report

Site

identification

Sample

date(s)

Depth

to water

(feet)

Approximate age and

lithologic unit near well screen

Type of

data
APPENDIX B 61

209 384318106470001 06/12/1974 -- -- FP, MI, TE, N

210 384418106513601 08/27/1976 -- Holocene alluvium FP, MI, TE, N

211 384423106512001 08/27/1976 17.0 Holocene alluvium FP

212 384446106423601 06/12/1974 15.0 Holocene valley-fill sand FP, MI, TE, N

213 384447106503701 10/28/1976 20.0 Holocene alluvium FP, MI, TE, N

214 384450106503601 10/28/1976 58.0 Upper Jurassic Entrada Sandstone FP, MI, TE, N

215 384518106284201 08/23/1976 11.0 Holocene alluvium FP, MI, TE, N

216 384531107012701 06/10/1976

08/16/1977

15.0

--

Upper Cretaceous Mesaverde limestone --

FP, MI, TE, N

217 384553107030601 10/13/1976 10.0 Upper Cretaceous Mesaverde limestone FP, MI, TE, N

218 384646107035801 06/10/1974 -- -- FP, MI, TE, N

219 384720106522701 08/27/1976 -- Holocene alluvium FP

220 384751106524401 06/07/1974 -- Holocene valley-fill sand FP, MI, TE, N

221 384815106523000 08/26/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

222 384827106530200 05/14/1997

10/08/1997

0.8

1.45

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

223 384849106375101 06/14/1974 17.0 Precambrian Erathem FP, MI, TE, N

224 384851106534700 05/13/1997

10/07/1997

1.79

16.5

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

225 384852106521200 08/26/1997 -- Cenozoic valley-fill alluvium FP

226 384913106514001 06/07/1974 12.0 Holocene valley-fill sand FP, MI, TE, N

227 385009106555101 06/06/1974 32.0 Precambrian metamorphic rock FP, MI, TE, N

228 385123106574801 06/07/1974 -- Holocene valley-fill sand FP, MI, TE, N

229 385124106562200 05/13/1997

10/07/1997

4.55

10.4

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

230 385125106571900 08/06/1997 -- Holocene valley-fill alluvium FP, MI, TE, N, R

231 385204107020001 08/09/1978 -- -- FP, MI, TE, N

232 385213106584700 12/05/1996

05/12/1997

10/07/1997

--

8.6

12.05

Holocene valley-fill alluvium FP, MI, TE, N, R

FP, MI, TE, N, R

FP, MI, TE, N, R

233 385345107002000 08/06/1997 5.0 Holocene valley-fill alluvium FP, MI, TE, N, R

234 385351107002501 04/29/1977 -- Upper Cretaceous Mancos Shale FP, MI, TE, N

Appendix B. Characteristics of ground-water-quality sites in the upper Gunnison River watershed, 1970–99—Continued

[FP, field properties; MI, major ions; TE, trace elements; N, nutrients; R, radon]

Site number

for this report

Site

identification

Sample

date(s)

Depth

to water

(feet)

Approximate age and

lithologic unit near well screen

Type of

data