REPORT OF HYDROLOGIC INVESTIGATIONS IN THE THREE SISTERS 

AREA OF CENTRAL OREGON, SUMMER 2001. 

By William C. Evans1, Robert H. Mariner1, Steven E. Ingebritsen1, B. Mack Kennedy2, 

Matthias C. van Soest2

, and Mark A. Huebner1

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 02-4061 

1

U.S. Geological Survey, Menlo Park, CA 

2

Lawrence Berkeley National Laboratory, Berkeley, CA 

Menlo Park, California 

2002 
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: 

William C. Evans 

U.S. Geological Survey 

345 Middlefield Rd. 

Menlo Park, California 94025 

i
CONTENTS 

Abstract................................................................................................................................ 

Introduction............................................................................................................................ 

Background............................................................................................................................ 

Procedures............................................................................................................................. 

Results.................................................................................................................................. 

Comparisons with Past Data.................................................................................................... 

 Chloride/Bromide Ratios........................................................................................................ 

Alkalinity and Dissolved Inorganic Carbon................................................................................... 

Carbon: Isotopes and Sources.................................................................................................. 

 Gas Results........................................................................................................................ 

Discussion.............................................................................................................................. 

Effects of Intrusion?.............................................................................................................. 

Heat and Carbon Discharge..................................................................................................... 

New Data and the Conceptual Model......................................................................................... 

The Need for Cold Spring Studies............................................................................................. 

Conclusions............................................................................................................................ 

Acknowledgements................................................................................................................... 

References............................................................................................................................. 

 

FIGURES 

1. Map showing the volcanic peaks of the High Cascades, major drainages, and hot springs of the Western 

 Cascades..................................................................................................................... 

2. Spring and stream locations with conductivity values in upper and lower Separation Creek area, July 

 2001......................................................................................................................... 

3. Temperature vs. elevation for three spring groups in the Separation Creek drainage compared to the 

regional data for springs with no Cl

-

 anomaly.......................................................................... 

4. Bromide vs. chloride in Separation Creek waters compared to hot springs of the Oregon Cascades.......... 

5. Bicarbonate and dissolved inorganic carbon vs. chloride in springs of the Separation Creek drainage....... 

6. Carbon isotope plot of three springs in the Separation Creek drainage and the soda spring to the 

 southeast.................................................................................................................... 

7. Temperature vs. chloride with regession lines for three spring areas in the Separation Creek drainage...... 

8. Conceptual model of the Separation Creek drainage.................................................................. 

TABLES 

1. Locations where water analyses were performed and results........................................................ 

2. Analyses of gas bubbles collected from springs....................................................................... 

3. Dissolved inorganic carbon and isotopic results...................................................................... 

APPENDIX........................................................................................................................... 

1 

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1 

4 

4 

4 

6 

6 

6 

7 

8 

8 

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9 

10 

10 

11 

11 

2 

3 

4 

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13

ii
Report of Hydrologic Investigations in the Three Sisters Area 

of Central Oregon, Summer 2001. 

By William C. Evans1, Robert H. Mariner1, Steven E. Ingebritsen1, B. Mack Kennedy2, Matthias C. van Soest

2

, 

and Mark A. Huebner1 

1

U.S. Geological Survey, Menlo Park, CA 

2

Lawrence Berkeley National Laboratory, Berkeley, CA 

ABSTRACT 

An ongoing episode of crustal uplift 

centered in the Separation Creek drainage of the 

Three Sisters area, central Oregon Cascades, 

may result from a magmatic intrusion that began 

in 1998. An investigation of springs in this 

drainage in summer 2001 revealed slightly 

elevated water temperatures and chloride (Cl-

) 

concentrations of up to about 5 ̊C and 20 

milligrams per liter (mg/L), respectively, above 

background. The total discharge of anomalous 

Cl-

 in Separation Creek was 9.2 grams per 

second, which in combination with the 

temperature-Cl-

 relation in the springs results in 

a total advective heat discharge of 16 MW

(megawatts). Comparison with similar findings 

obtained a decade earlier suggests that total Cland heat discharges in the groundwater drainage 

are unaffected by the current uplift. However, 

the isotopic composition of the dissolved 

inorganic carbon (DIC) in the spring waters 

(delta carbon-13 (δ13C) = -9.03 to -11.6‰; 

carbon-14 (14C) <25 pmC) combined with 

helium-3/helium-4 (3He/4He) ratios near 8 RA

and C/3

He ratios <1010 in two of the springs are 

indicative of a magmatic source. The high 3

He/4He ratios indicate that the magmatic gas is 

derived from a relatively recent, if not ongoing, 

intrusion. The concentration of magmatic carbon 

is low, a few millimoles per liter (mmol/L) at 

most, with an average value of 1.53 mmol/L for 

all the springs sampled in the drainage. 

Combining this average with the late-summer 

water flow in Separation Creek suggests a 

discharge of 21 tonnes/day of magmatic carbon 

dioxide (CO2). The presence of magmatic 

carbon in the shallow groundwater system, and 

the fact that DIC is uncorrelated with Cl-

, 

suggests that some magmatic gas could escape 

diffusely through the soils. 

INTRODUCTION 

Crustal uplift in the Three Sisters area was first 

detected by Wicks and others (2001) using InSAR

imagery. That imagery reveals uplift over a broad circular 

region, with maximum rise at the center reaching 4-5 

cm/yr. The uplift is centered several km west of the 

Cascades crest, at a location lacking young volcanic vents. 

However, discharge of thermal fluid in this area was 

recognized a decade prior to the onset of uplift on the basis 

of a Cl

-

 anomaly in Separation Creek, which drains the 

western flanks of South Sister (fig. 1). 

In response to the detection of crustal uplift, USGS 

scientists conducted an investigation of springs and 

streams in the Separation Creek drainage, which includes 

the area of maximum uplift, from 8 to 16 July 2001. The 

main goal of the work was to check the water for 

geochemical anomalies that would reflect enhanced upflow of either thermal water or magmatic gases, two

processes that might accompany intrusion, especially at the 

shallow depth of 6-7 km proposed by Wicks and others 

(2001; 2002). This study was carried out in collaboration 

with noble-gas experts from the Lawrence Berkeley

National Laboratory (LBNL). 

BACKGROUND 

Streams flowing over volcanic rocks of the Cascade 

Range normally have chloride concentrations within or 

near the range of average values in local precipitation

(typically 0.2-0.7 mg/L), unless they have received some

thermal fluid input. Reconnaissance sampling of lower 

Separation Creek on 11/17/89 revealed an anomalous Cl

-

concentration of 1.6 mg/L (Ingebritsen and others, 1994, p. 

33). Further sampling and stream gaging on 9/12/90 

confirmed an anomalous Cl

-

 flux of about 10 g/s in

Separation Creek (Ingebritsen and others, 1994, p. 59), 

comparable to that associated with hot springs of the 

Western Cascades, such as Breitenbush and the nearby

McKenzie River group (fig. 1). 

The anomalous Cl

-

 flux in Separation Creek was 

originally suspected to derive from input of thermal water 

similar to that discharging from the hot springs. The 

undiscovered hydrothermal source was thus expected to

have a Cl

-

 concentration on the order of 103 mg/L and to

occur at low elevation on Separation Creek, near the 

confluence with Horse Creek, because all of the known 

1
Horse Crk.

Separation Crk.

Figure 1. Map showing the volcanic peaks of the High Cascades, major drainages, and hot springs of the Western Cascades 

(modified from Ingebritsen and others, 1994, to show Separation and Horse Creeks).

Western Cascades hot springs occur at the bottom of major 

stream valleys (fig. 1), between elevations of 460 and 760 

m. Later sampling expeditions in 1990 and 1998 

(Ingebritsen and others, 1994; Iverson, 1999) instead 

traced the source of Cl-

 up Separation Creek and several of 

its tributaries to a large number of springs widely

distributed through the drainage, at elevations ranging 

from 1050 to 1850 m. The most concentrated springs 

contained about 20 mg/L Cl

-

 and were only a few degrees 

above ambient temperature for the discharge elevation 

(Iverson, 1999). During these studies, much information 

was compiled on groundwater geochemistry, stream

discharges, and dissolved loads, making Separation Creek 

an exceptionally well-characterized drainage compared to 

many in the Cascade Range. Anomalies resulting from the 

current episode of crustal uplift can be more easily 

distinguished from pre-existing conditions because of this 

large database (see Appendix for a compilation of data

2
3

Figure 2a. Spring and stream 

locations with conductivity

values in upper Separation

Creek area, July 2001. Location

of maximum uplift shown. See

key for symbol explanation.

Figure 2b. Spring and stream

locations with conductivity

values in lower Separation

Creek area, July 2001. See

key on Fig. 2a for symbols.
collected prior to 2001). However, some areas of the 

watershed remain to be sampled for geochemistry, even 

after the work described herein.

PROCEDURES 

Up-flow of thermal water brings dissolved salts into

overlying shallow groundwater, increasing its conductivity

and providing an easy means of detecting water that

contains even a trace of thermal fluid. Conductivity was 

measured with a portable meter at many springs and 

streams. Other field measurements included temperature, 

dissolved oxygen, pH, and alkalinity. A few 

measurements of CO2 in soil gas at 10 cm depth were 

made at selected locations by driving in a tube and 

connecting it to a pump and portable infrared sensor. 

Water samples were collected from springs with the 

highest conductivity within a given spring group and from

a few springs with lower conductivity. All water samples 

were filtered on-site through 0.45 μm filters. One bottle 

was acidified to pH~2 with high-purity nitric acid for 

subsequent cation analysis by inductively coupled plasma

mass spectrometry. A second bottle was left unacidified 

for subsequent anion analysis by ion chromatography. 

Two of the springs with the warmest temperatures 

and highest conductivities produced streams of gas 

bubbles, which were collected in pre-evacuated Pyrex 

tubes. Separation Creek was gaged and sampled upstream

from its confluence with Horse Creek by the USGS 

Oregon District during the week following the sampling. 

Samples were also collected from a non-thermal mineral

(soda) spring located about 10 km southeast of the 

Separation Creek drainage (fig. 1), and noble gas samples 

were collected from several hot and soda springs at lower 

elevations in central Oregon. 

RESULTS 

Locations where conductivity was measured along 

with the results are shown in figure 2. Conductivities 

ranged from 5 to 228 μS/cm, with the lowest value 

measured in the upper reach of Hinton Creek, probably 

representing glacial melt-water. Iverson (1999), in the 

course of his USGS-sponsored senior honors thesis

research, demonstrated that Cl-

 exceeded background 

values in waters with conductivities ≥40 μS/cm (his fig. 1). 

Although it should be noted that HCO3

-

 is the main anion

responsible for conductivity in all waters sampled, the 40-

μS/cm value can reasonably be used to distinguish waters 

with anomalous chloride from the regional background. 

Figure 2 shows that anomalous waters discharge 

throughout the area above 1050 m elevation but apparently

not in upper James Creek or in Separation Creek above 

Separation Creek Meadows. The maximum conductivity

(228 μS/cm) was found in the Indian Holes area, very

close to the center of crustal uplift, but a value of 217 

μS/cm was found in the upper Mesa Creek area, several

km to the southeast.

Sites where additional analyses were performed are 

distinguished by diamond symbols in figure 2, and the 

results are shown in table 1. Dissolved O2 (oxygen) values 

are given both in mg/L and as percent of air-saturation at

the temperature of the spring. Temperature anomalies are 

difficult to recognize in table 1 because of the large range 

in elevations and the fact that both springs and streams 

were sampled. Comparison with the regional temperatureelevation relation for cold springs given by Ingebritsen and 

others (1994) suggests that maximum anomalies are about

5 ̊C in the springs (fig. 3). The anion results in table 1 

show the change with elevation noted by Iverson (1999):

Cl-

 exceeds SO4

-2 (sulfate) in lower elevation springs, 

whereas SO4

-2 is dominant above 1600 m.

The gas collected from the two bubbling springs is

dominated by an air-like component, as shown in table 2. 

Compared to atmospheric air, the gas is significantly 

enriched in He (helium), slightly enriched in CO2, and 

depleted in O2. The helium isotopes show a strong 

magmatic signature. Dissolved Inorganic Carbon (DIC) 

speciation and isotopes are shown in table 3. The few 14C 

values available show that the DIC in those springs is 

dominated by dead carbon, whereas the δ13C values of all 

the springs analyzed are heavier than expected for DIC in 

shallow groundwater. 

Lower Springs

Indian Holes

Upper Mesa Crk.

Figure 3. Temperature vs. elevation for three spring 

groups in the Separation Creek drainage (block arrows) 

compared to the regional data for springs with no Cl

-

anomaly (open squares) and regression line from

Ingebritsen and others (1994; their fig. 21). Block arrows 

include data from Appendix. 

Comparisons with Past Data 

The pattern of anomalous conductivities (fig. 2) is 

similar to that found in 1998 by Iverson (1999). For 

example, he found a low conductivity (14 μS/cm) in upper 

James Creek and conductivities up to 207 μS/cm in the 

Indian Holes area and up to 180 μS/cm in springs near the 

confluence of Separation, Honey, and Sphinx Creeks (near 

VH20RM01). In the upper Mesa Creek area (near 

VH10BE01) conductivities were anomalous in 1998 but 

less than 100 μS/cm. Several springs were found to have 

conductivities exceeding 100 μS/cm in 2001, suggesting 

4
Table 1. Locations where water analyses were performed (as shown on fig. 2) and results. 

Sample # Name elev. t cond. D.O. O2 Sat. pH HCO3 Cl SO4 Br 

m (°C) μS/cm mg/L % mg/L mg/L mg/L mg/L 

VH02BE01 Unnamed spring 1746 2.9 56 10.3 93 6.05 27 1.54 2.1 0.005 VH03BE01 Hinton Creek 1742 8.6 50 1.58 2.9 0.004 VH04BE01 Head of unnamed creek (rockfall) 1771 2.7 63 11.6 105VH05BE01 Indian Holes spring (lower meadow) 1483 7.8 228 - 197 8.6 86 8.04 85 20.5 6.8 0.056 VH06BE01 Separation Creek 1525 6.8 68 2.1 2.1 0.006 VH07BE01 Indian Holes spring on hillside 1525 5.5 173 10.6 101 7.80 90 7.4 2.9 0.020 VH08BE01 Spring near Separation Meadows 1737 2.8 44 10.5 94 6.43 27 0.85 1.03 0.003 VH09BE01 Unnamed spring 1855 2.8 64 10.2 92 5.60 29 2.2 4.1 0.006 VH10BE01 Spring at upper end of Mesa Meadows 1755 7.8 217 5.5 56 8.03 93 7.0 18 0.021 VH11BE01 Large discharge spring 1687 3.5 90 7.60 39 3.3 5.6 0.010 VH20RM01 Unnamed spring (low on Separation Creek) 1110 11.2 180 8.65 85 12.6 3.0 0.035 VH21RM01 Unnamed spring (low on Separation Creek) 1110 9.2 130 67 6.7 1.66 0.018 VH22RM01 Separation Creek at foot bridge 957 44 3.0 1.62 0.003 VH23KL01 Separation Creek at gage site (0.1 km below br.) 952 7.4 83 36VH27BE01 Soda spring southeast of South Sister 1800 5.64 506 5.3 16.7 0.013 

Values for HCO3 are alkalinity as bicarbonate. Anion analyses performed by Mark Huebner, tritium by Robert Michel, both USGS, Menlo ParkTable 2. Analyses of gas bubbles collected from springs. 

van Soest at

Analyses of δ C by L. D. White, USGS, Menlo Park, CA. An

Lawrence Livermore National Laboratory. Biogenic carbon w

Helium isotopic analyses by Mack Kennedy and MatthiasLawrence Berkeley National Laboratory. 

Table 3. Dissolved inorganic carbon and isotopic results. 

vol-% VH05BE01 VH10BE01 standard air

He 0.0095 0.0050 0.0005

H2 <0.0002 <0.0002 <0.0002

Ar 0.989 1.018 0.934

O2 16.93 11.30 20.95

N2 81.24 86.19 78.08

CH4 <0.0002 <0.0002 <0.0002

CO2 0.1078 0.0879 0.0365

C2H6 <0.0002 <0.0002 <0.0002

H2S <0.0005 <0.0005 <0.0005

CO <0.001 <0.001 <0.001

C3H8 <0.0005 <0.0005 <0.0005

C4H10 <0.0005 <0.0005 <0.0005

N2/Ar 82.1 84.6 83.6

He/He(air) 19 10 1

O2/O2(air) 0.81 0.54 1

3He/4He (RA) 7.4 8.6 1

13 

Sample HCO3- DIC δ13C-DIC 14C 

mmol/L mmol/L per mil PDB pmC 

VH02BE01 0.44 1.82VH05BE01 1.39 1.47 -11.49 22.2 VH07BE01 1.48 1.56 -9.72VH08BE01 0.44 1.16 -10.00VH09BE01 0.48 4.24 -9.30 5.85 VH10BE01 1.52 1.54 -9.03 10.3 VH11BE01 0.64 0.68 -11.43VH20RM01 1.39 1.40 -11.59VH21RM01 1.10VH22RM01 0.72VH27BE01 8.29 59.8 -9.84 1.11 
Fi

com

t

area. The Cl

springs in the W

1989; R. H. Mariner, written com

6

onds) and dissolved inorganic 

oride in springs of the 

 concentration measurements at 10 

o 0.75%), 

 soils in healthy forest and due

s and soil microbes (see, e.g., 

tz and others, 1985). 

15 20 25

mg/L)

0

1

DIC (mmol/L)

HCO3

-

that some change has occurred in the upper Mesa Creek 

area. The area near VH11BE01 was not visited in 1998. 

The Cl- and SO4

-2 values in 2001 (table 1) were also 

similar to those of Iverson (1999) for most spring areas. 

The exception is again the upper Mesa Creek area, where 

VH10BE01 has more than twice the Cl

-

 and SO4

-2 values 

found in any of the springs sampled here in 1998. In 

comparing present results to those of Iverson (1999), note 

that all anion analyses were performed in the same

laboratory using the same instrument. Previous Cl

-

 and 

SO4

-2 values are given in the Appendix and are shown in

map format at http://wwwrcamnl.wr.usgs.gov/volcwater/. 

Spring temperatures we measured were also similar 

to those of Iverson, as was the tendency for temperature 

anomalies to correlate with Cl-

 within any given spring 

group (Iverson, 1999, his fig. 2). 

Chloride/Bromide Ratios 

Bromide, like chloride, is considered to be a 

conservative element in dilute groundwater. Water 

samples collected in 2001 were analyzed by a sensitive ion 

chromatography technique whereby Br

-

 could be detected 

down to about 1 μg/L, sufficiently low that the Cl

-

/Br- ratio

could be determined for all of the samples. This ratio, 

shown in figure 4, is remarkably constant in the samples, 

including the mineralized soda spring southeast of the area. 

The only sample that plots significantly off the correlation 

line was collected from the lower reach of Separation 

Creek, and this probably reflects selective removal of trace 

levels of Br-

 by biologic or sorption processes (see Davis 

and others, 1998) in the channel during the long flow 

downstream. Excluding this point, the regression line has 

an R2

 of 0.997, and the average Cl

-

/Br- mass ratio is 368. 

romide vs. chloride in Separation Creek waters 

o hot springs of the Oregon Cascades. 

rong correlation between Cl

-

 and Br

-

 suggests 

mon source throughout the study -

/Br- ratio is within the range found in the hot

estern Cascades (Mariner and others, 

munication). 

Alkalinity and Dissolved Inorganic Carbon 

Gaseous CO2 has a moderate aqueous solubility at 

low temperatures. Cold groundwaters that encounter CO2

rising from sources at depth can absorb large quantities of

the gas. The high-TDS soda spring located about 10 km

southeast of the study area is an example of a groundwater 

that has absorbed so much CO2 that free gas bubbles 

exsolve vigorously out of solution at the spring vent. 

Dissolved CO2 is not a conservative component, 

however. It reacts with silicate minerals to form HCO3

-

, 

which accounts for nearly all the alkalinity in these waters. 

The concentration of HCO3

-

 in cold groundwater depends 

in part on the amount of CO2 that dissolves into the water 

and on the time that elapses before the water discharges at 

a spring. If no CO2 is lost from the groundwater and no 

carbonate minerals precipitate (or dissolve), then the molar 

DIC, which is the sum of the CO2, HCO3

-

, and CO3

-

, is 

conserved during flow to the discharge point. These two 

conditions may be met for the dilute groundwaters in the 

study area, and so it is worthwhile to compare DIC and 

another conservative constituent, such as Cl-

. 

Figure 5 shows a plot of HCO3

-

 and DIC against Cl-. 

The HCO3

-

 concentration shows only a general correlation, 

and the DIC no correlation, with Cl

-

. Both HCO3

-

 and DIC

show only a weak correlation with SO4

-2 as well. 

Although additional sampling is needed to fill in gaps in 

the plots, the existing data show that CO2 source strength 

is not well linked with the thermal water up-flow, which

transports the Cl-

. 

Figure 5. Bicarbonate (diam

carbon (open squares) vs. chl

Separation Creek drainage. 

Carbon: Isotopes and Sources 

The soil-gas CO2

cm depth averaged 0.40% (range of 0.08% t

fairly typical of well-drained

to respiration by plant root

Reardon and others, 1979; Fri

gure 4. B

pared t

The st

hat they share a com

0

1

2

3

4

5

0 5 10

Cl- (

HCO3

- (mmol/L)

2

3

4

5

DIC
-25

-20

-15

-10

-5

0

δ13C-DIC

magmatic

DIC

biogenic

DIC soda

spring

Separation

Crk. springs

0 0.2 0.4 0.6 0.8 1

abiogenic fraction

Groundwater that recharges through these soils dissolves

some of this CO2. To distinguish this shallow, biogenic 

compo

e 

elative 

the iss

ay of 14C within the 

quifers can be ignored, and the DIC in springs that

ion processes should 

ave modern C values. Any depletion in 14C from

moder h. 

of

springs in the Separation Creek drainage correspond well

a

C of -9‰ for the deep, abiogenic C. The -9‰ value is 

2-3‰

Howe

The up-flow 

of mag

3

He/4He ratios of 7.4 and 8.6 at Indian Holes and upper 

Mesa Creek, respectively, are among the highest in the 

Cascades. The magmatic origin of the helium is clear, but

volatile species from depth otherwise constitute a minor

fraction of the total gas phase. At the greater than neutral

pH of both springs, most of the DIC is present as HCO3

-

and not CO2. 

The reason that bubbles form in these springs is that

the waters are slightly warmer than background, in part

through the small admixture of thermal fluid. Assuming 

that the waters recharged as snowmelt, they have warmed 

by nearly 8 ̊C prior to discharge. This temperature rise 

causes a 15-20% reduction in the solubilities of N2, O2, and 

Ar; and so the water, originally saturated with air gases at 

0 ̊C, forms bubbles even though some of the dissolved O2

has reacted away underground. The N2/Ar ratio remains 

unchanged from the air value. 

The composition of the gas bubbles can be used, 

along with the water temperature and ambient pressure, to

calculate the concentrations of the various gases dissolved 

feeding the spring. The calculation 

se

ssolved in these springs 

ctually forms into bubbles. The good agreement between 

e O2/O2(air) in the bubbles (table 2) and the percentdissolved oxygen

robe (table 1) further supports this assumption. For He, 

the cal

and DIC (table 3) gives C/ He ratios of 5 x 10 and 9 x 10 , 

nent from any deep-seated component, isotopic 

analysis of the DIC is required. For the coniferous forest

area here, the δ13C value of soil CO2 is expected to be near

-20‰ (Reardon and others, 1979; Fritz and others, 1985;

Evans and others, 2002). The heavy δ13C values of th

DIC in the springs (table 3) clearly reflect an input of 

deep-seated carbon, but until its δ13C is known, the r

proportions of shallow and deep carbon cannot be 

calculated. 

A few 14

C analyses were obtained to help resolve 

ue. The residence time of most shallow 

groundwater in the upper Separation Creek drainage is

probably <50 years, based on tritium values in table 1. 

This is short enough that radio-dec

a

acquire CO2 only from soil respirat 14 h

n values results from addition of carbon from dept

The bomb-related spike and subsequent decline in

atmospheric 14C during the past 50 years is a slight

complication because 14C in soil CO2 tracks the 

atmospheric values and also exceeds the defined “modern 

carbon”. Assuming an average groundwater flow time

about a decade suggests that biologically produced DIC in

these springs should have a 14C of about 115% modern. 

On that basis, the 14C values in table 3 can be used to break

down the DIC into biogenic and abiogenic components. 

Clearly, most of the DIC in the samples is abiogenic, and

very little error is introduced by the uncertainty in the 

assumed 14C of the biogenic end member. 

Figure 6 shows the δ13C values plotted against the 

fraction of the DIC that is abiogenic. The three cold 

Figure 6. Carbon isotope plot of three springs in the 

Separation Creek drainage and the soda spring to the 

southeast. The mixing line assumes a δ13C of -9‰ for

magmatic carbon. 

to a line that assumes a δ13C of -20‰ for biogenic C and 13 δ

lighter than both the average δ13C value (-6.5‰) 

found (Sano and others, 1995) in mid-ocean ridge basalt 

(MORB) and the δ13C of CO2 gas from Newberry caldera 

(Carothers and others, 1987), southeast of Three Sisters. 

One possible source for the deep carbon is thermal

breakdown of organic compounds in meta-sedimentary

rocks buried deep beneath the Three Sisters volcanics.

ver, CO2 from summit hot springs or fumaroles at 

many other Cascades volcanoes is similarly light

isotopically. Mt. Hood, Mt. St. Helens, and Mt. Rainier to

the north, and Mt. Shasta to the south of the Three Sisters 

area, all have δ13C values between –9 and –12‰ (Evans 

and others, 1981; unpublished USGS data). At Mt. St. 

Helens, the light CO2 was collected directly from erupted

magma. Together with the helium isotopic data, the 

carbon isotopes suggest that the abiogenic component of

the DIC derives from an up-flow of magmatic CO2. 

Based on the mixing line in figure 6, the δ13C values 

in table 3 suggest that the DIC in all of the springs is

dominated by a magmatic carbon component.

matic CO2 is apparently widespread through the 

area even though none of the springs contains a high 

concentration of DIC.

Gas Results 

As noted by van Soest and others (2001), the 

in the groundwater

assumes that the gas bubbles are in equilibrium with the 

water at the spring vent. Equilibrium is likely becau

probably <20% of the gas di

a

th

saturation measured in the water with the

p

culated aquifer concentrations are 0.032 and 0.017 

μmol/L for VH05BE01 and VH10BE01, respectively.

Combining these concentrations with the 3

He/4He ratios 3 9 9

7
respectively, for the two springs. These low ratios, which

are near the 2 x 109

 value typically found in MORB (Sano 

and others, 1995), add further support for a magmatic

carbon source. 

DISCUSSION 

Effects of Intrusion? 

One of the main questions to address is whet

there have b

her 

een changes in the groundwater system of the 

Separa

s direct

d

son

r

ould 

either a

 a 

kground Cl

-

conce

in

Some types of analyses, such as carbon speciation, 

were not previously performed in this area, making it

difficult to evaluate temporal changes. Changes in HCO3

-

can be ruled out because of the strong effect such changes 

would have on conductivity. Dissolved CO2, however, 

does not contribute to conductivity and constitutes an 

important fraction of the DIC in some of the waters (fig.

5). Moreover, DIC does not appear to correlate with Cl

-

, 

rendering a comparative approach speculative. Our carbon 

speciation measurements, and the carbon and helium

isotopic work, serve as a basis for studying future changes. 

Heat and Carbon Discharge 

Although none of the springs in the drainage are 

more than ~5 ̊C above the expected ambient value for a 

particular elevation, the total water flow from all of the 

springs is large enough that the advective heat transport is

substantial. The general correlation between Cl-

 and 

temperature for springs in the drainage (fig. 7) allows 

advective heat transport to be calculated from the Cl-

 

ines 

for thr

ite (3.0 – 0.5 = 2.5 mg/L) and the 

ischarge (3.6 m3

/s). Figure 7 suggests a range of about

er  ̊C above local ambient temperature 

r the different spring areas. Assuming the average value 

(2.5 m f 16

een 44 and 45 15’ N latitude could be ~156 

MW, t

er, 

of 1.72 mmol/L. The three 

that ha e 

nnual

tion Creek drainage since 1998, when the surface

uplift began (Wicks and others, 2002). As far a

comparison is possible with the available temperature, 

conductivity, and chemistry data, no significant changes

are apparent. Small but detectable changes seem to be 

restricted to the upper Mesa Creek area, where Cl

- an

SO4

-2 values have increased. Both anions are 

proportionally increased from values reported by Iver

(1999), indicating that the deep fluid component has 

remained compositionally similar over the three-yea

period. The increased Cl-

 and SO4

-2 concentrations c

indicate that, in this part of the drainage, there is

slight increase in up-flow of the deep fluid, or simply less 

dilution of the deep fluid by shallow groundwater because 

of the dry conditions in 2001. 

For the entire drainage, the data suggest that any

changes in the groundwater system have been small, even 

extending back to September 1990 when lower Separation

Creek was gaged and sampled. Discharge and Cl

- were 3.5

m3

/s and 3.3 mg/L, respectively, at that time, resulting in

total anomalous Cl-

 load of 10 g/s if the bac

ntration is assumed to be 0.5 mg/L. Discharge and 

Cl- were 3.6 m3/s and 3.0 mg/L in July 2001, resulting

an anomalous Cl

-

 load of 9.2 g/s, not significantly different

from the 1990 result.

Figure 7. Temperature vs. chloride with regression l

ee spring areas in the Separation Creek drainage

(solid symbols from Iverson (1999; his fig. 2); open 

symbols from table 1). 

anomaly at the gaging s

d

1.5 - 4 mg/L Cl

- p

fo

g/L/ ̊C) gives a total advective heat transport o

MW with an uncertainty of about a factor of two. This is

greater than the advected heat in many of the major hot

spring systems in the Oregon Cascades (for example, the 

Breitenbush system). However, Ingebritsen and others 

(1994) hypothesized that the total heat advected by lowtemperature groundwater systems of the central Oregon

Cascades betw o o

en times the amount in the Separation Creek 

drainage. This total represents an advective heat flow of

~1.1 MW/km-arc-length over 140 km. Manga (1998) 

documented a comparably large low-temperature advective

heat flow of ~0.6 MW/km-arc-length south of South Sist

for the east side of the arc only. 

The total discharge of magmatic carbon can also be 

calculated for the drainage. The 8 cold springs for which

we have DIC data (table 3) show a range of 0.68 – 4.24 

mmol/L with an average value

ve 14C analyses suggest that on average, 89% of th

carbon is magmatic. Combining these values suggests an 

average magmatic DIC of 1.53 mmol/L. If all of the 3.6 

m3

/s water at the gaging site reflected flow from such 

springs, the total magmatic carbon discharge through 

groundwater in the drainage would be 21 tonnes/day as

CO2. 

The stream-discharge value of ~3.5 m3

/s – obtained 

both in 1990 and 2001 – is likely less than the mean a

stream flow, because both measurements were made under 

mid- to late-summer (low flow) conditions. Nevertheless,

8
Figure 8. Conceptual model of the Separation Creek drainage (modified from Iverson, 1999). Up-flow of water from a 

hydrothermal reservoir beneath the western flank of South Sister feeds heat and Cl

-

 into the overlying groundwater system. 

Steam and gas from the reservoir affect the higher elevation groundwater. The H2S oxidizes to SO4

-2, while CO2 is 

gradually and variably converted to HCO3

-

 through reaction with silicate minerals. 

a CO2 discharge of 21 tonnes/day is likely to be a 

maximum estimate. One reason is that the spring with the 

lowest DIC, VH11BE01, had by far the largest discharge 

of all the springs sampled. In addition, the magmatic 

carbon discharge cannot be normalized to the Cl

-

concentration at the gaging site, as was done for the heat

transport, because DIC does not correlate with Cl-

 in the 

springs (fig. 5). To the extent that some of the water flow 

at the gaging site does not result from spring input

(Iverson, 1999) or may result from springs with no 

magmatic DIC, the 21 tonnes/day figure may overestimate 

the total discharge. 

Magmatic carbon discharges of this magnitude were 

postulated to exist on the western side of the Cascades by

James and others (1999), who found similar discharges in

several large spring systems east of the crest. Their data 

show that other, long-dormant central Oregon volcanoes 

support carbon discharges comparable to that in the 

Separation Creek drainage. There is thus no evidence that 

requires the magmatic carbon discharge in Separation 

Creek to be linked with the ongoing crustal uplift. Larger 

carbon discharges have been measured at Lassen Peak 

(>28 tonnes/day) and Mammoth Mountain (50 tonnes/day)

in California (Sorey and others, 1998; Evans and others, 

2002), both of which have shown unrest within the past

100 years. 

New Data and the Conceptual Model 

Data acquired over the past two decades link the 

low elevation hot springs of the western Cascades to 

outflows from hydrothermal systems beneath the Cascade 

crest, most likely at reservoir temperatures of 100-180 ̊C 

(Mariner and others, 1990; Ingebritsen and others, 1994). 

Iverson (1999) applied this model to the Separation Creek 

drainage, suggesting that thermal water leakage from a 

hydrothermal reservoir at fairly high elevations on the 

western flank of South Sister accounted for the Cl

-

anomaly in the lower elevation springs, and that sulfur-rich 

vapors boiling off this reservoir gave rise to the SO4

-2

anomaly in the higher elevation springs. Our new results

support this model, shown in figure 8. 

There is no evidence for vapor-phase transport of 

Cl- as HCl. Vaporization of HCl from Cl

-

-containing 

thermal waters becomes significant at temperatures above 

250 ̊C (Truesdell and others, 1989), and drilling in nearby 

Newberry caldera (Sammel, 1983) has shown that

hydrothermal systems might reach such temperatures in 

the Cascade volcanoes without giving rise to vigorous 

surface features such as boiling springs. However, 

vaporization of the halogens would likely fractionate Cl

-

and Br

-

. The uniform Cl-/Br- ratio in all the cold springs, 

and the fact that this ratio falls within the range for the 

9
low-elevation hot springs (fig. 4), argues strongly that the therefore be the first hydrologic features to respond to

Cl-

 anomaly results from input of thermal liquid. 

The lack of correlation between Cl-

 and HCO3

-

 or 

DIC (fig. 5) suggests that a gas/vapor zone rich in CO2

does overlie the liquid reservoir, allowing CO2 to dissolve 

into shallow groundwaters independently of any inputs of 

Cl-

-rich thermal water. An extensive vapor zone would, in

addition, allow any H2S gas to oxidize to SO4

-2, explaining 

the distinct patterns in each of the SO4

-2, Cl-

, and DIC

anomalies. This hypothesis would also predict that waters 

rich in sulfate should be, in part, steam-heated, a possible 

explanation for the steeper slope of the temperature-Clrelation in the upper Mesa Creek springs (fig. 7) relative to

the other spring areas. 

The reservoir may be the same one that feeds the 

low-elevation hot springs in the Western Cascades (as 

assumed in fig. 8) or may be a separate, adjacent or 

superjacent system. Additional geochemical constraints 

are needed to address this. We note that the temperatureCl-

 relations (fig. 7) for the Indian Holes and lower springs 

groups extrapolate to about 500-700 mg/L Cl

-

 at 180 ̊C, 

the maximum reservoir temperature estimated for the lowelevation hot-spring systems to the west (Mariner and 

others, 1990; Ingebritsen and others, 1994). If the hot

springs, which contain ~1200-1350 mg/L Cl

-

, are fed from

this same reservoir, then additional Cl-

 must be added 

along the outflow paths. Some interaction with

sedimentary rocks may occur, explaining the CH4, highN2/Ar ratios, and relatively lower 3

He/4He ratios in the hot

springs (R. H. Mariner, written communication). 

Because CO2 apparently reaches the shallowest 

levels of groundwater flow, the possibility exists that some

of the CO2 escapes directly to the atmosphere, particularly 

at higher elevations where the water table may be 

relatively deep. Diffuse efflux measurements in the upper 

Separation Creek drainage should therefore be continued. 

The obvious comparison is Mammoth Mountain in

California, where several hundred tonnes per day of CO2

diffuse out through the volcano’s flanks (Sorey and others, 

1998; Gerlach and others, 1999; Rogie and others, 2001), 

while ~50 tonnes/day are transported by cold groundwater 

(Evans and others, 2002). The main difference between 

the two cases is that many of the cold springs at Mammoth 

Mountain are nearly saturated with CO2, which may be a 

necessary condition for diffuse emissions to occur. 

The Need for Cold Spring Studies 

In instances where volcanic unrest or intrusion is

suspected, water sampling frequently focuses on hot

springs as the obvious surface manifestation of volcanic 

heat. In the central Oregon Cascades, however, the hot

springs are connected to the hydrothermal reservoir 

through long outflow paths that would likely retard 

recognition of any changes in reservoir conditions. In 

contrast, heat and gases released from intruding magma 

may cause a rapid increase in vapor flux from the top of 

the reservoir. Much or all of the rising steam and gas may

be absorbed in cold groundwaters with much shorter 

subsurface residence times. Springs fed by cold 

groundwater systems on or near the volcanic edifice may

unrest.

Detailed sampling of cold groundwaters may also 

provide information about magmatic characteristics that

are not obtainable by other means. The Separation Creek 

sampling suggests that magmatic carbon in the Three 

Sisters area has a δ13C ratio of about –9‰, lighter than the 

global average for magmatic carbon but similar to several

other volcanoes in the Cascades. The C/3He ratio in the 

area seems to be <1010, fairly close to the MORB range. 

Although more sampling for helium isotopes is needed, a 

low C/3

He ratio limits the amount of crustal or subducted 

carbon that might be involved. Recognition of these 

geochemical signatures may prove invaluable to future 

studies; for example, to identify the source of any diffuse 

CO2 emissions. These ratios can sometimes be difficult to 

interpret at hot or highly mineralized soda springs because 

of extensive degassing in the vent areas or calcite

precipitation in the aquifers. 

CONCLUSIONS 

Our investigation of springs and streams in the 

Separation Creek drainage reveals that the anomalous 

discharge of thermal fluid and heat is similar in magnitude 

to that obtained prior to the current episode of crustal

uplift. The total discharge of anomalous Cl

-

 remains at 

~10 g/s; the total advective heat anomaly at ~16 MW. 

Up to about 20 tonnes/day of magmatic CO2 are 

absorbed and transported by the cold groundwater as DIC. 

This amount is substantial, but apparently not atypical of 

central Oregon volcanoes (James and others, 1999), and 

discharges of this magnitude may be more common at

dormant volcanoes than is currently recognized. If we 

assume that the CO2 derives from magma with a density of 

2.7 g/cm3

 and an initial CO2 content of 0.65 wt-% (e.g., 

Gerlach and Graeber, 1985; Lowenstern, 2001), the 

discharge represents complete degassing of about 0.0005 

km3

 of magma per year. Similarly, the 16-MW heat

anomaly could be supplied by crystallization and cooling 

of about 0.0003 km3

 of magma per year, assuming the 

conditions given in Ingebritsen and Sanford (1998, p. 183). 

These figures may be representative of the long-term

intrusion rate for the area rather than the current rate. 

Elastic models of the uplift invoke magma intrusion at a 

much higher rate of ~0.006 km3

/yr beginning in 1998 

(Wicks and others, 2002). 

Although none of the anomalous characteristics we 

observed are necessarily tied to the current uplift, the cold

groundwater system is nevertheless strongly influenced by

magmatic inputs, as evidenced by 3

He/4He ratios near 8 RA

and C/

3

He ratios ≤1010 in two of the springs. A recent 

input of mantle basalt would normally be invoked to

explain such ratios in a continental setting (see e.g., 

Kennedy and Truesdell, 1996). All of the analyzed springs 

contain magmatic carbon, in concentrations uncorrelated 

with Cl-

, suggesting that a shallow zone of gaseous CO2 is 

widespread through parts of the area. 

The new data support the conceptual model

proposed by Iverson (1999), who called for a vapor zone to

overlie a liquid hydrothermal reservoir on the western 

10
flanks of South Sister. The cold springs in the Separation 

Creek drainage that contain a small component of thermal

fluid are likely to be the first hydrologic features to change 

in response to intrusion and are clear candidates for future 

monitoring studies in this region. 

ACKNOWLEDGEMENTS: 

The helium isotopic analyses were performed at 

Lawrence Berkeley National Laboratory, Center for 

Isotope Geochemistry. The 14C analyses were performed 

at Lawrence Livermore National Laboratory, Center for 

Accelerator Mass Spectrometry. Yousif Kharaka and 

Shaul Hurwitz provided helpful reviews of the manuscript.

REFERENCES: 

Carothers, W. W., Mariner, R. H., and Keith, T. E. C., 

1987, Isotope geochemistry of minerals and fluids 

from Newberry Volcano, Oregon: Journal of 

Volcanology and Geothermal Research, v. 31, p. 47-

63. 

Davis, S. N., Whittemore, D. O., and Fabrycka-Martin, J., 

1998, Uses of chloride/bromide ratios in studies of 

potable water: Ground Water, v. 36, p. 338-350. 

Eruptions of Mount St. Helens, Washington,: U.S. 

Geological Survey Professional Paper 1250, pp. 227-

231. 

, B. M., 

SA:

es on 

r,

ioxide 

.

Ingebritsen, S. E. and Sanford, W. E., 1998, Groundwater 

in Geologic Processes. Cambridge University Press, 

Cambridge, 341 pp. 

Iverson, J. T., 1999, An investigation of the chloride 

anomaly in Separation Creek, Lane County, Oregon. 

Unpublished senior honors thesis, Oregon State 

University, Corvallis, 61 pp.

James, E. R., Manga, M., and Rose, T. P., 1999, CO2

degassing in the Oregon Cascades: Geology, v. 27, p. 

823-826. 

Kennedy, B. M. and Truesdell, A. H., 1996, The 

Northwest Geysers high-temperature reservoir:

evidence for active magmatic degassing and 

implications for the origin of The Geysers geothermal

field: Geothermics, v. 25, p. 365-387. 

Lowenstern, J. B., 2001, Carbon dioxide in magmas and 

implications for hydrothermal systems: Mineralium

Deposita, v. 36, p. 490-502. 

Manga, M., 1998, Advective heat transport by lowtemperature discharge in the Oregon Cascades:

Geology, v. 26, p. 799-802. 

,

ctonic environment. Proceedings of 

Workshop XLIV, Geological, Geophysical, and 

Tectonic Setting of the Cascade Range, Dec. 1-4, 

1988, edited by L. J. P. Muffler, C. S. Weaver, and D. 

Report 89-178, p. 663-694. 

le,

nal

L., Chiodini, G.,

an

ia:

cil, v. 

Secular variations of carbon and helium isotopes at

Evans, W. C., Banks, N. G., and White, L. D., 1981, 

Analyses of gas samples from the summit crater, in. 

Lipman, P. W. and Mullineaux, D. R., eds., The 1980 

Mariner, R. H., Presser, T. S., Evans, W. C., and Pringle

M. K. W., 1989, Discharge rates of thermal fluids in

the Cascade Range and their relationship to the

geologic and te

Evans, W. C., Sorey, M. L., Cook, A. C., Kennedy

Shuster, D. L., Colvard, E. L., White, L. D., and 

Huebner, M. A., 2002, Tracing and quantifying 

magmatic carbon discharge in cold groundwaters:

Lessons learned from Mammoth Mountain, U

Journal of Volcanology and Geothermal Research, v.

115, (in press). 

Fritz, P., Mozeto, A. A., and Reardon, E. J., 1985, 

Practical considerations on carbon isotope studi

soil carbon dioxide: Chemical Geology, v. 58, p. 89-

95. 

Gerlach, T. M. and Graeber, E. J., 1985, The volatile 

budget of Kilauea, Hawaii: Nature, v. 313, p. 273-277.

Gerlach, T. M., Doukas, M. P., McGee, K. A., and Kessle

R., 1999, Airborne detection of diffuse carbon d

emissions at Mammoth Mountain,California:

Geophysical Research Letters, v. 26, p. 3661-3664

Ingebritsen, S. E., Mariner, R. H., and Sherrod, D. R., 

1994, Hydrothermal systems of the Cascade Range, 

north-central Oregon: U. S. Geological Survey

Professional Paper 1044-L, 86 pp. 

D. Blackwell: U. S. Geological Survey Open-File 

Mariner, R. H., Presser, T. S., Evans, W. C., and Pring

M. K. W., 1990, Discharge rates of fluid and heat by

thermal springs of the Cascade Range, Washington, 

Oregon, and northern California: Journal of 

Geophysical Research, v. 95, p. 19,517-19,531. 

Reardon, E. J., Allison, G. B., and Fritz, P., 1979, Seaso

chemical and isotopic variations of soil CO2 at Trout

Creek, Ontario: Journal of Hydrology, v. 43, p. 355-

371. 

Rogie, J. D., Kerrick, D. M., Sorey, M.

d Galloway, D. L., 2001, Dynamics of carbon 

dioxide emission at Mammoth Mountain, Californ

Earth and Planetary Science Letters, v. 188, p. 535-

541. 

Sammel, E. A., 1983, The shallow hydrothermal system at

Newberry Volcano, Oregon: a conceptual model:

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7, p. 325-330. 

Sano, Y., Gamo, T., Notsu, K., and Wakita, H., 1995, 

11
Izu-Oshima Volcano, Japan: Journal of Volcanology

and Geothermal Research, v. 64, p. 83-94. 

D.,

in

on in

on,

: Eos, Transactions of the American Geophysical

U t

W., 

cher,

ity

,

Sorey, M. L., Evans, W. C., Kennedy, B. M., Farrar, C.

Hainsworth, L. J., and Hausback, B., 1998, Carbon 

dioxide and helium emissions from a reservoir of 

magmatic gas beneath Mammoth Mountain, 

California: Journal of Geophysical Research, v. 103, 

p. 15,303-15,323. 

Truesdell, A. H., Haizlip, J. R., Armannsson, H., and 

D’Amore, F., 1989, Origin and transport of chloride

superheated geothermal steam: Geothermics, v. 18, p. 

295-304. 

van Soest, M. C., Kennedy, B. M., Evans, W. C., and 

Mariner, R. H., 2001, Helium isotope compositi

springs from the Three Sisters region, central Oreg

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nion, v. 82 (47), Fall Meeting Supplement, Abstrac

V51C-1028. 

Wicks, C. W., Dzurisin, D., Ingebritsen, S., Thatcher,

Lu, Z., and Iverson, J., 2001, Magmatic activity

beneath the quiescent Three Sisters volcanic center, 

central Oregon Cascade Range, USA, inferred from

satellite InSAR: Eos, Transactions of the American

Geophysical Union, v. 82(47), Fall Meeting 

Supplement, Abstract G31C-0155. 

Wicks, C. W., Jr., Dzurisin, D., Ingebritsen, S., That

W., Lu, Z., and Iverson, J., 2002, Magmatic activ

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12
APPENDIX 

UTM N UTM W Elevation Date

Pre-2001 data for selected springs and streams in the upp

Justin Iverson; RHM = Robert Marine 

4880731 587425 1025 Aug-98

er Separatio

JI =

n Creek watershed.

2 JI-50 Sep. Cr. above confluence with Sphinx Cr.

2 JI-55-57 Sep. Cr. below confluence with Sphinx Cr.

0.6 JI-52-54 Sphinx Cr. above confluence with Sep. Cr.

Temp. Na Cl 

m m m deg. C mg/L mg/L m

3.3 0.6

4883640 592840 1730 Aug-98 1.95 us

48835 1.96 3.3 JI-2 spring emerging from talus

2

1.33

1.21

1.34 spring, may be same as 70

1 2 RHM sample

.29

.88

4883440 592630 1695 Sep-98 3.1 1.19

Sep-98 3.6 1.27

Sep-98 3.2 0.95

4883310 593230 1745 Sep-98 4.1 1.83

4.7 Indian Holes

488 6.9

488 8.9

488 10

488 18.6 dian Holes

488 588590 1090 Sep-98 7 3.9 1.9 JI-82 low-flow woodland spring

4881460 588650 1100 Sep-98 6.1 5.4

12.1

448 12.6 st below orifice, joins with 84?

488 12.6 low orifice at trail crossing

488 <1.00

4881293 587687 1055 9/11/1990 24.3 12.4

2.7

488 12.4

488

487 0.2 <

487

Stre

488 580048 705 3/28/1990 3.6 0.6

4885940 580048 705 3/28/1990 5.8 2.2

2.3

2.3

488 0.6 George Cr. at trail

488 1.97

488 0.8

488 2.3

488 0.58 Cr.

488 0.26

488 815 3/28/1990 6.3 2.5

4882482 582651 840 9/11/1990 7.3 3.1 Sep. Cr.

3.3

488 3.2

488 5.1

488 5

488 588650 1220 Sep-98 7.4 4.6 JI-87 Honey Cr., main channel just above fork and falls

4881819 583699 925 9/11/1990 4.1 0.6 Separation Lake tributary

2.9

488

4881526 589688 1135 Aug-98 2.9

.6

3

488 .3 Sep. Cr. at trail bridge, Q = 3,560 L/s

488 0.68 0.4 JI-62 Middle Fork of Mesa Cr.

488 3.2

4880744 587250 1010 Aug-98 3.3

1.45

SO4 Notes

g/L

3 JI-1 spring emerging from tal

Springs

4885855 580217 740 3/28/1990

60 592250 1730 Aug-98

4883510 592840 1720 Sep-98 3.8

4883490 592630 1705 Aug-98

4883490 592580 1705 Aug-98

4883490 592750 1720 Sep-98 3

4883476 594780 1910 8/12/1981 3 4.2

4883460 592700 1720 Sep-98 3.4 1

4883460 592300 1660 Sep-98 4.7 0

3.3 JI-69 spring, taken above confluence

2.2 JI-3 spring orifice emerging from wooded hillside

2.1 JI-4 spring orifice emerging from wooded hillside

2.2 JI-71

2.2 JI-70 spring 50 m down stream from 69

1.5 JI-75 spring/trib

2 JI-73 spring, may be same as 72

2.1 JI-72 spring

1.6 JI-74 spring

2.7 JI-68 spring, taken above confluence

4883410 592580 1695

4883400 592490 1660

4882866 591414 1500 9/11/1990 9.3

2860 591690 1485 Sep-98 4.9

2780 591610 1485 Sep-98 5.9

2740 591550 1480 Sep-98 5.9

2680 591340 1480 Sep-98 9.3

1490

2.7 JI-77 spring, small woodland, first of the Indian Holes

3.3 JI-78 spring, joins with 77 along with others

3.7 JI-79 spring system

6 JI-80 spring, lowermost of In

1.8 JI-81 low-flow woodland spring

3 JI-84 lower spring E at orifice

3 JI-85 lower spring, central, ju

3.1 JI-86 lower spring, W just be

4881410 587790 1080 Sep-98 10.8

1410 587730 1085 Sep-98 12.1

1410 587650 1105 Sep-98 11.1

1366 594875 1755 8/12/1981 3 5.2 2 RHM sample

7.5 JI-63 N. Fork of Mesa Cr., easternmost spring

Q = 26 L/s

0.4 JI-58 spring-fed tributary to Sep. Cr.

1.00 RHM ('81), LS ('87)

Cedar Swamp

Louise Cr. above Sep. Cr.

Sep. Cr. above Louise Cr.

Sep. Cr. above Louise Cr.

Sep. Cr.

4881280 595060 1755 Sep-98 4.7

1243 587557 1060 9/11/1990 10 24.4

0620 586950 1005 Aug-98 1.01

6878 599108 1725 8/15/1987 3 2.6

6218 583600 1165 Sep-86 3

ams

6024

4885699 580120 715 3/28/1990 6.1

4885072 580361 740 3/28/1990 6

3723 582000 915 3/28/1990 3.3

3667 594438 1840 Sep-98 3.6

3663 581675 790 3/28/1990 3.6

3554 581627 790 3/28/1990 5.7

3385 592050 1645 Sep-98 7

2974 593650 1780 Sep-98 6

2723 582265

3.2 JI-67 N. Fork Hinton Cr.

George Cr. at confluence with Sep. Cr.

Sep. Cr. above George Cr.

0.9 JI-76/12 Sep. Cr. above confluence with Hinton

0.5 JI-91 James Cr.

Sep. Cr.

4882436 590950 1460 Aug-98

2282 590588 1370 Aug-98

2256 589500 1280 Sep-98 7.6

2154 589063 1270 Sep-98 7.5

2128

2.1 JI-19-21 Sep. Cr. above Indian Hole Falls

2.1 JI-22 Sep. Cr.

2 JI-89 Honey Cr.

1.9 JI-88 Honey Cr.

1.9

4881590 589975 1205 Aug-98

1564 590150 1220 Aug-98 2.5

2.3 JI-28-30 Sep. Cr. below confluence with Mesa Cr.

2.5 JI-25-27 Mesa Cr. above confluence with Sep. Cr.

2.3 JI-31 Sep. Cr.

1.8 JI-83 Honey Cr. above confluence with Sep. Cr.

2.2 JI-32 Sep. Cr., below two small woodland spring inputs

4881513 588425 1075 Sep-98 7.8 4

4881436 589100 1095 Aug-98

1150 584747 950 9/11/1990 7.6 3

0795 594775 1745 Sep-98 9.2

0782 587400 1025 Aug-98

13