GEOTHERMAL HYDROLOGY OF

VALLES CALDERA AND THE 

SOUTHWESTERN JEMEZ MOUNTAINS,

NEW MEXICO

U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 00-4067

Prepared in cooperation with the 

OFFICE OF THE STATE ENGINEER

GEOTHERMAL HYDROLOGY OF 

VALLES CALDERA AND THE 

SOUTHWESTERN JEMEZ 

MOUNTAINS, NEW MEXICO

By Frank W. Trainer, Robert J. Rogers, and Michael L. Sorey

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 00-4067

Prepared in cooperation with the 

OFFICE OF THE STATE ENGINEER

Albuquerque, New Mexico 

2000
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, 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:

District Chief 

U.S. Geological Survey 

Water Resources Division 

5338 Montgomery NE, Suite 400 

Albuquerque, NM 87109-1311

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Information Services 

Box 25286 

Denver, CO 80225-0286

Information regarding research and data-collection programs of the U.S. Geological Survey is available 

on the Internet via the World Wide Web. You may connect to the Home Page for the New Mexico District 

Office using the URL: http://nm.water.usgs.gov
CONTENTS

Page

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

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

Purpose and scope......................................................................................................................... 3

Previous investigations and availability of data............................................................................ 3

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

Regional setting..................................................................................................................................... 5

Geography..................................................................................................................................... 5

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

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

Wles Caldera.......................................................................................^ 11

Geology......................................................................................................................................... 11

Hydrologic setting......................................................................................................................... 13

Nonthermal ground water............................................................................................................. 14

Surface and near-surface geothermal features............................................................................... 15

Thermal meteoric water........................................................................................................ 15

Acid sulfate water................................................................................................................. 17

Hydrothermal alteration........................................................................................................ 24

Geothermal anomaly............................................................................................................. 24

Geothermal reservoir..................................................................................................................... 26

Geometry and hydrologic properties.................................................................................... 26

Areal extent................................................................................................................... 28

Thickness...................................................................................................................... 29

Temperature and pressure distributions........................................................................ 29

Hydraulic properties..................................................................................................... 30

Geochemistry of geothermal fluids....................................................................................... 32

Fluid flow in the reservoir..................................................................................................... 35

Southwestern.JemezMountains............................................................................................................ 37

Descriptive hydrochemistry.......................................................................................................... 39

Mixtures of water.......................................................................................................................... 39

Mineral water near the caldera as derivatives of geothermal fluids.............................................. 46

Mineral water in Canon de San Diego.......................................................................................... 50

Area near rim of caldera....................................................................................................... 53

Jemez Springs and Soda Dam............................................................................................... 58

Fluctuations in constituent concentrations............................................................................ 62

Stable isotopes as evidence of mixing.................................................................................. 68

Origin of mineral water................................................................................................................. 68

Wells GT-2, PC-1, and PC-2................................................................................................. 68

Well VC-1............................................................................................................................. 75

Jemez Springs and Soda Dam............................................................................................... 78
Page 

Ground-water system............................................................................................................................. 79

Principal aquifers........................................................................................................................... 79

Canon de San Diego San Ysidro area......................................................................................... 80

Discharge from the geothermal reservoir...................................................................................... 89

Ground-water underflow....................................................................................................... 90

Conduit flow in bedrock........................................................................................................ 90

Streamflow............................................................................................................................ 91

Perched ground water in bedrock.................................................................................................. 93

Quantitative modeling of the geothermal system.................................................................................. 94

Conceptual models of the geothermal system............................................................................... 95

Existing numerical models............................................................................................................ 96

Quantitative constraints................................................................................................................. 97

Modeling system response to development................................................................................... 99

Monitoring hydrochemical discharge in the southwestern Jemez Mountains....................................... 101

Historical monitoring............................................................................................................................. 10

Summary.......................................................................................^

Selected references.................................................................................................................................! 11

FIGURES

1-7. Maps showing:

1. Geographic setting of the Jemez Mountains region........................................................... 4

2. Generalized geology of the Jemez Mountains and adjacent Rio Grande

Rift zone........................................................................................................................... 7

3. Regional geologic setting of the Jemez Mountains............................................................ 9

4. (A) Geologic features in the Valles Caldera and (B) generalized geologic

section of the Valles Caldera............................................................................................ 10

5. Location of selected geothermal boreholes and hot springs in the Valles Caldera

region............................................................................................................................... 12

6. Principal streams in the Valles Caldera region and location of discontinued

U.S. Geological Survey streamflow-gaging stations....................................................... 12

7. Location of selected sampling sites for deuterium and oxygen-18 data listed in

table4.............................................................................................................................. 22

8. Graph showing deuterium and oxygen-18 data for selected waters in the Jemez

Mountains region.................................................................................................................. 22

9. Generalized section of the Sulphur Springs area, Valles Caldera............................................ 23

10. Maps showing (A) areal extent of hydrothermal alteration and the geothermal reservoir

and (B) shallow temperature gradients in the Valles Caldera............................................... 25

11. Generalized section of southwestern Valles Caldera and upper Canon de San Diego

showing the active geothermal system ................................................................................. 27

12-25. Graphs showing:

12. Temperature profile of seven Baca wells............................................................................ 30

13. Range of concentrations of geothermal-reservoir fluids collected in 1982 from five

Baca wells....................................................................................................................... 34

14. Relation of deuterium and oxygen-18 for selected thermal and nonthermal fluids in

the Jemez Mountains region............................................................................................ 34

iv
Page

15. (A) Major-ion composition and (B) concentrations in water from geothermal wells

in the Sulphur Springs and Redondo Creek areas........................................................... 40

16. (A) Major-ion composition and (B) concentrations in water from wells and springs 

in granitic rocks, volcanic rocks (chiefly rhyolitic and andesitic), and alluvium and 

colluvium derived from volcanic rocks........................................................................... 41

17. (A) Major-ion composition and (B) concentrations in water from wells and springs

in the Madera Limestone................................................................................................. 42

18. (A) Major-ion composition and (B) concentrations in water from wells and springs

in the Abo Formation...................................................................................................... 43

19. (A) Major-ion composition and (B) concentrations in water from wells and springs

in rift-fill deposits (Santa Fe Formation and Zia Sand)................................................... 44

20. Downstream change in major-ion composition of water in the Jemez River system

and map showing location of sampling sites................................................................... 45

21. Major-ion composition in ground water in alluvium along the Jemez River and

map showing location of sampling sites ......................................................................... 47

22. Concentrations of selected pairs of ions in geothermal-reservoir-fluid samples

and in mixed water.......................................................................................................... 48

23. Major-ion concentrations in geothermal-reservoir-fluid samples and estimated

original concentrations in water from well GT-2............................................................ 50

24. Actual analysis and reconstructed analysis of major ions in water from well PC-1.......... 51

25. Actual analysis and reconstructed analysis of major ions in water from well VC-1......... 52

26. Diagrammatic section showing generalized geohydrologic setting in Canon de

San Diego.............................................................................................................................. 52

27-36. Graphs showing:

27. (A) Major-ion composition and (B) concentrations in five ground-water samples

from Canon de San Diego near the rim of Valles Caldera.............................................. 55

28. Fluctuations in bicarbonate and chloride concentrations and discharge of spring

H-32 located near the rim of Valles Caldera, 1973-74.................................................... 57

29. (A,B) Fluctuations in concentrations of selected ions in spring H-32 and

(C) streamflow discharge at Jemez River below East Fork, near Jemez Springs............ 57

30. Ion-concentration and water-level fluctuations in wells H-29 and H-30, 1974 ................. 59

31. (A) Chloride and boron and (B) chloride and sulfate in water from wells and

springs in the Valles Caldera and Canon de San Diego area and (C) map showing 

location of wells and springs........................................................................................... 60

32. Actual and reconstructed concentrations of major ions in water from spring H-6

at Soda Dam and spring H-14 at Jemez Springs, 1972................................................... 62

33. Fluctuations in (A) 2-month running median concentrations of selected ions in 

springs, 1973-86 and (B) mean monthly streamflow in the Jemez River below 

East Fork, near Jemez Springs, 1963-76......................................................................... 64

34. Covariation of sulfate and chloride in reservoir fluids and in mineral water from the

Valles Caldera and Canon de San Diego......................................................................... 67

35. Covariation of deuterium and oxygen-18 in Valles Caldera reservoir fluids and in

derivative mixed waters................................................................................................... 71

36. Covariation of deuterium and oxygen-18 in water from geothermal wells in

Valles Caldera and wells VC-1 and GT-2 near the caldera rim...................................... 71
Page

37. Diagrams and graphs showing concentration of chloride in samples from water-yielding

zones penetrated by wells PC-1 and PC-2............................................................................ 73

38. Graph showing the effect on stable-isotope composition of geothermal-reservoir fluid 

from addition of small volumes of a hypothetical dilute water to one volume of 

reservoir water...................................................................................................................... 74

39. Graphs showing formation of mineral water similar to that in well VC-1 calculated

from stable-isotope data for inferred dilute water and geothermal-reservoir fluid............... 77

40. Diagrammatic cross section showing flow paths of reservoir fluid escaping from

VallesCaldera....................................................................................................................... 81

41. Graph showing (A) Inferred profiles of piezometric surfaces in Canon de San Diego 

and map showing (B) approximate water-table contours and generalized direction 

of ground-water movement in rift-fill deposits..................................................................... 82

42-45. Graphs showing:

42. Chloride load at three sites on the Jemez River, 1973-74.................................................. 83

43. Ranges in chemical composition of water from wells and springs in the lower

Canon de San Diego, near San Ysidro............................................................................ 84

44. Covariation of (A) lithium and chloride and (B) boron and chloride in

representative reservoir fluids in Valles Caldera and in mixed water in and

near Canon de San Diego................................................................................................ 88

45. Covariation of deuterium and oxygen-18 in reservoir fluid in Valles Caldera, 

derivative water near Canon de San Diego, and mineral-spring water near 

San Ysidro and Jemez Pueblo......................................................................................... 88

46. Diagram showing generalized pressure-altitude relations for liquid-dominated

hydrothermal systems........................................................................................................... 95

47. Map showing selected streamflow-gaging stations and periodic-measurement sites

where hydrologic measurements have been made................................................................ 103

48. Graph showing chloride load and sodium chloride molar ratio at the Jemez River

below East Fork, near Jemez Springs for 1963-67 and 1971-82 ..........................................104

49. Graph showing relation of major-ion composition in water samples from the Jemez

River and Rio Guadalupe Basins and wastewater from Fenton Hill drilling sites ...............107

TABLES

1. Generalized stratigraphy of Jemez Mountains in and near Valles Caldera................................... 8

2. Summary of selected physical data for hot springs and a geothermal well in Valles Caldera...... 16

3. Chemical analyses of thermal meteoric ground water in Valles Caldera...................................... 18

4. Deuterium and oxygen-18 isotope data for wells, springs, and streams in the

Jemez Mountains region.......................................................................................................... 19

5. Estimated reservoir properties of the Valles Caldera geothermal reservoir used in

numerical simulation models of the reservoir.......................................................................... 31

6. Chemical data used for estimating original major-ion concentrations of water from

well GT-2.................................................................................................^ 49

7. Chemical analyses of water from well PC-1................................................................................. 51

8. Chemical analyses of six ground-water samples, Canon de San Diego near the rim of

Valles Caldera.......................................................................................................................... 54

9. Discharge of the Jemez River upstream and downstream from Soda Dam.................................. 61

vi
Page

10. Chemical analyses of mineral water from wells and springs at Jemez Springs and

Soda Dam................................................................................................................................. 63

11. Example of degree of dilution calculated for typical mineral-water samples from Jemez

Springs and Soda Dam using two assumed parent reservoir fluids......................................... 65

12. Isotopic and chloride data for mineral water from wells and springs at Jemez Springs and

SodaDam...........................................^ 69

13. Chemical and stable-isotope data for well VC-1.......................................................................... 75

14. Calculated volume of dilute water that, when mixed with a unit volume of geothermal

fluid, yields water similar to that in well VC-1........................................................................ 76

15. Chemical and isotopic analyses of ground water in and near the lower Canon de

San Diego.................................................................................................^^ 85

16. Selected streamflow and chloride data and calculations for reach of Jemez River

between U.S. Geological Survey streamflow-gaging station Jemez River near Jemez

and San Ysidro, March 1,1984 ............................................................................................... 89

17. Chemical loads for selected ions in the Rio Grande, Otowi Bridge to Bernalillo........................ 92

18. Mean daily discharge at selected streamflow-gaging stations, February 11-15, 1974 ................. 92

19. Summary of characteristics and results of existing quantitative models of the Valles

hydrothermal system................................................................................................................ 98

20. Selected periodic measurement sites at which streamflow and water-chemistry data

have been collected..................................................................................................................102

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

Length

inch 

foot 

mile

2.54

0.3048

1.609

centimeter

meter

kilometer

Area

acre 

square mile

4,047

2.590

square meter 

square kilometer

Volume

gallon

gallon

acre-foot

3.785

0.003785

1,233

liter

cubic meter 

cubic meter

Flow rate

acre-foot per year

cubic foot per second

gallon per minute

0.03911

0.02832

0.06309

liter per second 

cubic meter per second 

liter per second

Mass

pound avoirdupois 0.4536 kilogram

vii
Multiply By To obtain

Pressure

pound per square inch 

bar

6.895 

100

kilopascal 

kilopascal

Density

pound per cubic foot 0.01602 gram per cubic centimeter

Energy

calorie 

megawatt

4.184 

1,000,000

joule 

joule per second

Specific capacity

gallon per minute per foot 0.2070 liter per second per meter

Transmissivity

feet squared per day 0.09290 meter squared per day

Permeability

millidarcy-foot

Temperature in degrees Celsius (°

3.01 x 10' 10

C) or degrees Fahrenheit (°

°F = (1.8x°Q + 32 

°C = (°F-32)/1.8

cubic centimeter (cm3)

F) can be converted by the equations:

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 a geodetic datum derived from a general adjustment of the first-order level nets of the United States and 

Canada, formerly called Sea Level Datum of 1929.

Concentration of stable isotopes in water are expressed in per mil relative to standard mean ocean 

water (SMOW), the normal reference standard.

Concentration of tritium in water is expressed in tritium units (TU), which equal 3.23 picocuries 

per kilogram of water.

Heat flow is expressed in heat flow units (HFU), which equal 3 x 10"6 calorie per centimeter squared 

per second.

viii
GEOTHERMAL HYDROLOGY OF VALLES CALDERA 

AND THE SOUTHWESTERN JEMEZ MOUNTAINS, 

NEW MEXICO

By Frank W. Trainer, Robert J. Rogers, and Michael L. Sorey

Abstract

The Jemez Mountains in north-central New 

Mexico are volcanic in origin and have a large 

central caldera known as Valles Caldera. The 

mountains contain the Valles geothermal system, 

which was investigated during 1970-82 as a source 

of geothermal energy. This report describes the 

geothermal hydrology of the Jemez Mountains 

and presents results of an earlier 1972-75 U.S. 

Geological Survey study of the area in light of 

more recent information. Several distinct types of 

thermal and nonthermal ground water are 

recognized in the Jemez Mountains. Two types of 

near-surface thermal water are in the caldera: 

thermal meteoric water and acid sulfate water. The 

principal reservoir of geothermal fluids is at depth 

under the central and western parts of the caldera. 

Nonthermal ground water in Valles Caldera occurs 

in diverse perched aquifers and deeper valley-fill 

aquifers.

The geothermal reservoir is recharged by 

meteorically derived water that moves downward 

from the aquifers in the caldera fill to depths of 

6,500 feet or more and at temperatures reaching 

about 330 degrees Celsius. The heated geothermal 

water rises convectively to depths of 2,000 feet or 

less and mixes with other ground water as it flows 

away from the geothermal reservoir. A vapor zone 

containing steam, carbon dioxide, and other gases 

exists above parts of the liquid-dominated 

geothermal zone.

Two subsystems are generally recognized 

within the larger geothermal system: the Redondo 

Creek subsystem and the Sulphur Creek 

subsystem. The permeability in the Redondo

Creek subsystem is controlled by stratigraphy and 

fault-related structures. Most of the permeability is 

in the high-angle, normal faults and associated 

fractures that form the Redondo Creek Graben. 

Faults and related fractures control the flow of 

thermal fluids in the subsystem, which is bounded 

by high-angle faults. The Redondo Creek 

subsystem has been more extensively studied than 

other parts of the system. The Sulphur Springs 

subsystem is not as well defined. The upper vapordominated zone in the Sulphur Creek subsystem is 

separated from the liquid-dominated zone by 

about 800 feet of sealed caldera-fill rock. Acid 

springs occur at the top of the vapor zone in the 

Sulphur Springs area. Some more highly 

permeable zones within the geothermal reservoir 

are interconnected, but the lack of interference 

effects among some wells during production tests 

suggests effective hydraulic separation along some 

subsystem boundaries. Chemical and thermal 

evidence suggests that the Sulphur Springs 

subsystem may be isolated from the Redondo 

Creek subsystem and each may have its own zone 

of upflow and lateral outflow.

The area of the entire geothermal reservoir 

is estimated to be about 12 to 15 square miles; its 

western limit generally is thought to be at the ringfracture zone of the caldera. The top of the 

reservoir is generally considered to be the bottom 

of a small-permeability "caprock" that is about 

2,000 to 3,000 feet below land surface. Estimated 

thicknesses to the bottom of the reservoir range 

from 2,000 to 6,000 feet. Reservoir temperatures 

measured in exploration wells range from 225 

degrees Celsius just below the caprock to about
330 degrees Celsius in deeper drill holes. 

Pressures measured in exploration wells in the 

Redondo Creek area ranged from 450 to 1,850 

pounds per square inch. Steam-producing zones 

have been encountered above the liquiddominated zones in wells, but the extent of steam 

zones is not well defined.

The reservoir contains a near-neutral, 

chloride-type water containing about 7,000 

milligrams per liter dissolved solids. No thermal 

springs in the caldera have geochemical 

characteristics similar to those of the geothermal 

reservoir fluids sampled in wells.

Oxygen-18 and deuterium isotope 

concentrations of geothermal reservoir fluid 

indicate a meteoric origin. The moat valleys in the 

north and east areas of the caldera may be the 

principal recharge zones of the reservoir. 

Downward flow along fault zones and fractures 

probably is the primary mechanism of recharge. 

Recharge water probably enters the edges of the 

reservoir at depth, heats up, rises convectively 

within the reservoir, and discharges laterally to the 

west and southwest.

Outflowing mineral water appears to be 

limited to the western and southwestern parts of 

the Jemez Mountains. Hydrothermal features 

outside Valles Caldera are restricted largely to 

Canon de San Diego. Subsurface escape of 

reservoir fluid from near and beneath Valles 

Caldera has formed a discharge plume of reservoir 

water mixed with dilute ground water, which 

extends down Canon de San Diego. The Jemez 

Fault Zone transports a relatively large portion of 

this flow. Soda Dam and Jemez Springs are 

derivatives of geothermal outflow from the 

reservoir. Near Jemez Pueblo, subsurface mineral 

water merges with the regional aquifer in fill 

deposits of the Albuquerque Basin.

Total geothermal discharge from the caldera 

is difficult to estimate; all estimates based on 

chemical mass balance suggest a small fluid 

discharge. About 1.0 cubic foot per second (ft3/s) 

of caldera-derived geothermal fluid is estimated to 

be carried by the Jemez River between Jemez 

Pueblo and San Ysidro, and about 0.4 ft3/s is 

estimated to be carried as underflow in the same

reach. Estimates of total discharge from the 

geothermal reservoir to the Rio Grande at its 

confluence with the Jemez River range from 2.0 to 

3.6 ft3/s.

Numerical models of the geothermal system 

range in complexity from one-dimensional, 

single-phase fluid-flow models to threedimensional, multiphase-fluid and heat-flow 

models. The models have been developed 

primarily to assess reservoir productivity and 

longevity and potential effects of development on 

thermal-water discharge in the Jemez River. A 

period of actual geothermal development, in which 

the system is stressed and the hydrologic changes 

are measured, is needed to calibrate or test the 

models. Existing models must be considered 

preliminary and cannot provide accurate answers 

to questions involving long-term changes to the 

geothermal system. No existing models account 

for the presence of carbon dioxide in reservoir 

fluid, which appears to be sufficient to markedly 

extend the depth over which two-phase conditions 

occur naturally and possibly to influence reservoir 

drawdown during development. Development of 

geothermal energy in Valles Caldera would 

probably change the hydrochemical discharge 

from the southwestern Jemez Mountains. 

Quantifying such changes through systematic 

monitoring would be valuable in better 

understanding the geothermal system and in 

testing, refining, and calibrating numerical models 

of the system.

INTRODUCTION

The Valles Caldera in the Jemez Mountains of 

north-central New Mexico (fig. 1) contains a 

geothermal system that has been investigated as a 

source of geothermal energy. This geothermal system 

has long been known from its thermal springs and 

fumaroles, but serious consideration of geothermal 

development did not begin until the early 1960's, when 

a test well being drilled for oil in the caldera yielded 

steam. The history of geothermal exploration that 

followed was summarized by Goldstein and others 

(1982). Geothermal exploration began in the 1960's 

with the drilling of four exploratory holes in the
Sulphur Springs area in the western part of the caldera. 

The potential of the geothermal system as an energy 

source was confirmed in 1970 with the drilling of a 

discovery well (Baca 4) in the Redondo Creek area of 

the caldera, southeast of Sulphur Springs. In 1971, 

Union Oil Company leased about 100,000 acres of 

privately owned land known as Baca Location No. 1 

(fig. 1) and began an active drilling program. Because 

most exploration was on the Baca property, the 

geothermal system is commonly referred to as the Baca 

geothermal field or reservoir; in this report, however, it 

is referred to as the Valles geothermal system. In 1978, 

the U.S. Department of Energy (DOE), Public Service 

Company of New Mexico (PNM), and Union Oil 

Company entered into a cooperative agreement to 

develop a 50-megawatt demonstration power plant at 

the Baca 4 site. In 1981, however, Union notified DOE 

and PNM that it could not locate sufficient steam to 

support a power plant. A modified program to test 

hydraulic fracturing of two marginal wells and drilling 

deeper wells was attempted with disappointing results, 

and in 1982 the project was terminated. Altogether, 

Union drilled more than 20 holes (referred to as the 

Baca wells) in the central and western parts of Valles 

Caldera, most in the Redondo Creek area, prior to 

terminating the project.

A range of geologic, geophysical, and 

hydrologic studies were conducted, principally by 

university and government scientists, during and 

subsequent to the period of active geothermal 

exploration in the Jemez Mountain region. This study, 

in cooperation with the Office of the State Engineer, 

was conducted during 1972-75 as part of the U.S. 

Geological Survey (USGS) geothermal research 

program. The Jemez Mountains region was selected for 

geohydrologic investigation by the USGS because 

exploratory drilling was in progress to evaluate the 

possibility of geothermal development in the region, 

and geohydrologic information would be of practical 

value. The region had been mapped geologically 

(Smith and others, 1970), but little was known about 

the geohydrology of hot-water geothermal systems in 

calderas such as the Valles Caldera.

The objectives of the 1972-75 USGS 

investigation were to (1) describe the geohydrology of 

the region; (2) examine the application of hydrologic 

methods to the study of a hot-water geothermal system; 

and (3) gather baseline hydrologic data to aid in 

identifying future hydrologic effects of geothermal 

exploration and development. To maintain suitable

water quality and quantity in the region, a better 

understanding is needed of the effects of the 

geothermal system in the caldera on ground water in 

the surrounding region. This investigation dealt 

primarily with areas of the Jemez Mountains outside 

the caldera because at the time this investigation was 

conducted, Union Oil Company had leased nearly the 

entire caldera and was not releasing information from 

its exploration activities.

Purpose and Scope

This report presents the results of the 1972-75 

USGS investigation of the geothermal hydrology of the 

Jemez Mountains region and discusses and reinterprets 

those results in light of more recent work and current 

(1996) understanding of the Valles geothermal system. 

The report also describes a conceptual geohydrologic 

model of the system and summarizes the results of 

previous hydrologic and geothermal studies of 

numerical simulations of heat and fluid flow in the 

geothermal and surrounding hydrologic systems.

The area described in the report is limited to the 

Jemez Mountains that contain geothermal 

water specifically Valles Caldera, which contains the 

principal geothermal reservoir and the southwestern 

Jemez Mountains region outside the caldera, which 

receives discharge from the geothermal reservoir and 

was the focus of the 1972-75 investigation.

Previous Investigations and Availability of 

Data

Previous investigations of the hydrology and 

geology of the Jemez Mountains region have focused 

on the region's extraordinary volcanic geology, its 

active and accessible geothermal system, the 

prospective development of this geothermal system as 

an energy source, and the potential environmental and 

hydrological effects of such development. When Union 

Oil Company entered into a cooperative agreement 

with the DOE in 1978, large amounts of information 

gathered on the caldera were made publicly available, 

and many scientific papers about the area were written. 

In the mid-1980's after geothermal exploration in the 

caldera ended, the geothermal system of Valles Caldera 

was investigated by the Continental Scientific Drilling 

Program (CSDP) of the National Academy of 

Sciences, which drilled three deep holes in the western
106°10

r-i_f

_ ±. _ J -

LOS ALAMOS COUNTY

R.1W. R.1E. R.10E.

10 15 20 MILES

10 15 20 KILOMETERS

Figure 1.--Geographic setting of the Jemez Mountains region 

(modified from Self and others, 1996, fig.V2b).
and southwestern parts of the caldera. Manifestations 

of anomalous heat flow in the western Jemez 

Mountains outside the caldera also have lead to drilling 

and research in this area. The use of geothermal heat to 

generate electricity by circulating fluid through a 

system of wells completed in manmade fractures in hot 

dry rock has been studied by the Los Alamos National 

Laboratory (LANL) at the Fenton Hill site just west of 

the caldera (fig. 1). The volume of data and scientific 

literature from these investigations is too large to 

summarize in detail; however, many important sources 

of information are contained in an annotated 

bibliography of the hydrology, geology, and 

geothermal resources of the Jemez Mountains region 

(Abeyta and Delaney, 1986), which covers the period 

through 1985. Two issues containing special sections 

on research in the Valles Caldera were published in 

Journal of Geophysical Research (1986, 1988). 

Hydrologic data for the Jemez Mountains region are 

included in USGS reports (1963-83), Trainer (1978), 

Union Oil Company of California and Public Service 

Company of New Mexico (1978), Goffand others 

(1982), Craigg (1984), Shevenell and others (1987), 

and Abeyta and Delaney (1990). Conover and others 

(1963), Griggs (1964), Purtymun and Cooper (1969), 

Dondanville(1971,1978), Trainer (1974,1978,1984), 

Goffand Grigsby (1982), and Goif and others (1988) 

described aspects of the hydrology of the region. The 

geochemistry of thermal water in the region and its 

derivatives have been discussed by Goffand others 

(1981), White and others (1984), Goffand others

(1985), Truesdell and Janik (1986), Vuataz and Goff

(1986), White (1986), and Shevenell and others (1987). 

Bodvarsson and others (1982), Faust and others (1984), 

and Grant and others (1984) developed conceptual and 

numerical simulation models of the geothermal system. 

Findings from holes drilled by the CSDP were 

summarized by Goffand others (1992) and discussed 

in detail by workers cited therein.

The entire Jemez Mountains region has been 

studied geologically. The western part of the region 

with special reference to sedimentary rocks was 

studied by Wood and Northrop (1946). Gardner and 

others (1986) and Smith and others (1970) studied the 

entire region with emphasis on volcanic rocks. The 

valley-fill deposits were investigated by Galusha and 

Blick (1971), and the tectonics of the region were 

reported by Aldrich (1986). The caldera and associated 

volcanism have been investigated by Nielson and 

Hulen (1984), Heiken and others (1986), and Self and

others (1986). Reiter and others (1975) and Swanberg 

(1983) mapped heat flow and temperature gradients in 

the region.

Acknowledgments

The 1972-75 USGS investigation of the Jemez 

Mountains region benefited from the cooperation of 

individuals, government agencies, and pueblos. 

Acknowledgments are extended to private land owners 

of the region, the holders of mineral rights in the Canon 

de San Diego Grant, the governors and councils of 

Jemez Pueblo and Zia Pueblo, LANL, the New Mexico 

Department of Game and Fish, and the U.S. Forest 

Service for access to and information about wells and 

springs; to Union Oil Company of California for the 

opportunity to collect and publish water-quality data 

for well Baca 4; and to Ivan Barnes, R.L. Borton, R.O. 

Fournier, F.E. Goff, W.E. Hale, J.L. Kunkler, R.H. 

Mariner, R.M. McBreen, Kim Ong, T.S. Presser, WD. 

Purtymun, C.S. Smith, A.H. Truesdell, F.G. West, and 

D.E. White for assistance in and discussion of the 

investigation.

REGIONAL SETTING

Geography

The Jemez Mountains encompass about 1,500 

square miles (mi2) in north-central New Mexico in Los 

Alamos, Rio Arriba, Sandoval, and Santa Fe Counties 

(fig. 1). The mountains form an oval topographic 

mound that contains a central caldera, or area of 

collapse, which is the most prominent feature of the 

mountains. The outer flanks of the caldera are 

surrounded by a series of plateaus dissected by narrow, 

deep canyons. The mountain mass is bounded by the 

principal streams that drain the region (fig. 1): the Rio 

Chama and Rio Puerco to the north, the Rio Grande to 

the east and southeast, and the Jemez River and 

tributaries to the south and west. The western boundary 

of the mountains joins the Nacimiento Mountains and 

consequently is not as clearly defined as the others. The 

highest point in the Jemez Mountains is Redondo Peak, 

11,254 feet (ft) above sea level (fig. 1).

Records of precipitation and temperature at 

several stations in and near the Jemez Mountains are 

published by the National Oceanic and Atmospheric
Administration. Mean annual precipitation in the lower 

country surrounding the mountain mass ranges from 

about 8 inches (in.) at the southern edge to 12 in. or 

more at the northern edge. Mean annual precipitation is 

about 18 in. at Los Alamos and about 17 in. at Jemez 

Springs. At both locations, approximately two-thirds of 

the annual precipitation falls during the 6-month period 

April through September (Kunkel, 1984). Annual 

precipitation at the higher altitudes near the center of 

the region, where few measurements have been made, 

is estimated from isohyetal analyses and topographic 

data to be greater than 30 in. (U.S. Soil Conservation 

Service, 1972). Most precipitation at the higher 

altitudes falls as snow, which lasts several months in 

winter and early spring. Vegetation ranges from desert 

plants in the areas surrounding the mountains to dense 

forests of conifers and aspen in the high country.

Nearly the entire caldera, or the central part of 

the mountains, is within the 100,000-acre Baca 

Location No. 1 (fig. 1). Most land outside the land grant 

is in public domain, administered principally by the 

U.S. Forest Service and the DOE. Small areas are 

administered by the New Mexico Department of Game 

and Fish and the National Park Service. Indian tribes 

own large tracts in peripheral parts of the region.

The total population of the Jemez Mountains 

region is probably less than 25,000. Most inhabitants 

live in Los Alamos and White Rock, which had 

populations of about 11,850 and 6,200, respectively, in 

1990. Several small villages (Jemez Springs, Canon, 

Ponderosa, and San Ysidro) are in the southwestern 

part of the region, and eight Indian pueblos (Jemez, 

Zia, Santa Ana, San Felipe, Santo Domingo, Cochiti, 

San Ildefonso, and Santa Clara) are situated along the 

Jemez River and Rio Grande. Santa Fe is located about 

30 miles (mi) to the southeast.

Geology

The Jemez Mountains are a complex mass of 

Tertiary and Quaternary volcanic rocks that overlie 

Tertiary, Mesozoic, and Paleozoic sedimentary rocks, 

which in turn overlie Precambrian basement rock 

(fig. 2; table 1). The volcanic field, which began 

forming about 13 million years ago (13 Ma), is located 

near the intersection of the Jemez Lineament and part 

of the western margin of the Rio Grande Rift (fig. 3). 

The Jemez Lineament is a northeast-trending chain of 

volcanic features extending from east-central Arizona 

to southeastern Colorado (Aldrich, 1986).

Formation of the Jemez volcanic field occurred 

as the result of two explosive eruptions that formed two 

calderas, Toledo Caldera and Valles Caldera, and led to 

the deposition of the Bandelier Tuff. The formation of 

the Valles Caldera, about 1.12 Ma, obliterated much of 

the older Toledo Caldera, which formed about 1.47 Ma. 

Heiken and others (1986) concluded that the Toledo 

Caldera was nearly coincident with the Valles Caldera 

and that the Toledo Embayment to the northeast 

(fig. 4 A) originally thought to be part of the Toledo 

Caldera is a tectonic feature or remnant of a smaller, 

even older caldera. The Valles geothermal system is 

located in the central and western parts of the Valles 

Caldera but does not extend under the entire caldera 

(Hulen and Nielson, 1986; Wilt and Vender Harr, 

1986). Extensive sheets of the Bandelier Tuff (fig. 4B) 

overlie the older rocks throughout much of the region, 

inside and outside the caldera, and form radially 

dissected plateaus that slope away from the caldera. 

West of the Rio Grande Rift the tuff overlies 

Precambrian crystalline rocks, Paleozoic and Mesozoic 

strata, and Tertiary volcanic rocks; within the Rio 

Grande Rift the tuff overlies Quaternary and Tertiary 

rocks (table 1).

Two major fault zones have a substantial 

influence on the hydrology of the region (Vuataz and 

Goff, 1986). The Pajarito Fault Zone is east of the 

caldera and forms the west side of the Rio Grande Rift. 

The Jemez Fault Zone in Canon de San Diego 

intersects the southwestern rim of the caldera (fig. 4 A). 

The Jemez Fault Zone is an expression of the Jemez 

Lineament, as are faulted structures crossing the 

resurgent dome and possibly the Toledo Embayment to 

the northeast (Self and others, 1986).

Hydrology

The Jemez Mountains are in the Rio Grande 

drainage basin. The topographic rim of Valles Caldera 

serves as a drainage divide and forms a near-circular 

drainage basin with a surface outlet on the southwest 

where the rim is breached. San Antonio Creek and the 

East Fork Jemez River are the principal streams 

draining the caldera, and they join near the southwest 

rim to form the Jemez River, which flows down Canon 

de San Diego, turns southeastward, and eventually 

joins the Rio Grande (fig. 1). Outside the caldera rim, 

streams flow radially outward to the principal 

drainages surrounding the mountains, the Rio Puerco, 

Rio Chama, Rio Grande, Jemez River, and Rio 

Guadalupe.
107°00' 106°30' 106°00'

25 MILES

25 KILOMETERS

EXPLANATION

I I 1 '

MIOCENE TO QUATERNARY 

SEDIMENTARY ROCKS OF MIDTO LATE CENOZOIC BASINS

VOLCANIC ROCKS LESS THAN 

15MILLONYEARSOLD

MISSISSIPPIAN TO EARLY MIOCENE 

SEDIMENTARY ROCKS, INTRUSIONS, 

AND VOLCANIC ROCKS

HIGH-ANGLE FAULT--Bar and ball 

on downthrown side were 

determined

CALDERA

K'--'l PRECAMBRIAN ROCKS

Figure 2.-Generalized geology of the Jemez Mountains and adjacent Rio Grande Rift zone 

(modified from Self and others, 1996, fig. V2a).
Table 1. Generalized stratigraphy of Jemez Mountains in and near Valles Caldera

[Sources of data: consolidated, nonvolcanic rocks outside Valles Caldera, Wood and Northrop (1946, sec. 4);

volcanic rocks, Smith and others (1961). In Valles Caldera, Conover and others (1963); Smith

and others (1970); Nielson and Hulen (1984); Wilt and Vonder Haar (1986, fig. 3).

Valley-fill deposits (in rift), Griggs (1964); Galusha and Blick (1971)]

Era

Cenozoic

Mesozoic

Paleozoic

Precambrian

Period

Quaternary

Tertiary

Triassic

Permian

Carboniferous

Group

Tewa 

Group

Polvadera 

Group

Keres 

Group

Magdalena 

Group

Jemez Plateau

Alluvial and 

landslide deposits; 

travertine

Bandelier Tuff

Tschicoma 

Formation

Paliza Canyon 

Formation

Basalt of Chamisa 

Mesa

Chinle Formation

San Andres, Yeso, 

and Abo 

Formations

Madera Limestone 

Sandia Formation

Granitic rocks

Valles Caldera

Alluvial, landslide, 

and lacustrine deposits

Valles Rhyolite and 

caldera-fill deposits

Bandelier Tuff and 

equivalent volcanic 

rocks

Tschicoma "Lower 

Formation tuffs"

Paliza Canyon 

Formation

Santa Fe Abiquiu 

Group Tuff

Abo Formation

Madera Limestone

Granitic rocks

Rio Grande Rift

Alluvial, landslide, and 

lacustrine deposits

Bandelier Tuff and equivalent 

volcanic rocks

El Rechuelos 

Rhyolite

Tschicoma 

Formation

Lobato Basalt

Bearhead Rhyolite

Paliza Canyon 

Formation

Canovas Canyon 

Rhyolite

Santa Fe Group 

Zia Sand

Puye 

Formation

Cochiti 

Formation

Abiquiu 

Tuff
110° 109° 108° 107° 106° 105°

37 C

36°

35°

34 C

100 MILES

100 KILOMETERS

EXPLANATION 

VOLCANIC ROCKS .'.'-V- BASINS OFTHE 

RIO GRANDE RIFT

Figure 3.-Regional geologic setting of the Jemez Mountains 

(modified from Goff and Shevenell, 1987, fig. 1).

Selected USGS streamflow-gaging stations in 

the Jemez Mountains area are shown below.

Station number Station name Period of record (inclusive)

08290000 Rio Chama near Chamita 

08313000 Rio Grande at Otowi Bridge

08319945 Redondo Creek near Jemez Springs 

08319950 Sulphur Creek near Jemez Springs

08321500 Jemez River below East Fork, 

near Jemez Springs

08323000 Rio Guadalupe at Box Canyon 

08324000 Jemez River near Jemez

October 1912 to present 

February 1895 to December

1905;

June 1909 to present 

November 1981

to September 1985 

November 1981

to September 1985 

July 1949 to October 1950; 

May 1951 to September

1957; March 1958 to

September 1976; July 1981

to September 1990 

May 1958 to September

1976

July 1981 to September 1996 

March 1953 to present

The Rio Chama enters the Rio Grande about 3.5 

mi north of Espanola. Mean annual flow at the Chamita 

gage (08290000), just upstream from its confluence 

with the Rio Grande, was 612 cubic feet per second 

(ft3/s) for water years 1971-98. Upstream from the 

gage, flow of the Rio Chama is regulated by reservoirs 

and irrigation diversions. The mean annual flow of the 

Rio Grande at Otowi Bridge (08313000) was 1,580

fVVs for water years 1971-98. Upstream from the gage, 

flow is regulated by reservoirs on the Rio Chama and 

irrigation diversions. The mean annual flow of the Rio 

Guadalupe at Box Canyon (08323000) was 54.5 ft3/s 

for water years 1982-96. The gaging station is located 

4.8 mi upstream from the confluence of the Rio 

Guadalupe and the Jemez River. The flow of the Rio 

Guadalupe is regulated by a small reservoir upstream 

from the gage and irrigation diversions. Mean annual 

flow of the Jemez River near Jemez (08324000), which 

is 0.7 mi downstream from the confluence with the Rio 

Guadalupe, was 79.6 ft3/s for water years 1954-98. 

Flow at the station is affected by upstream irrigation 

diversions.

Similarly to surface water, ground water flows 

radially outward from the rim of the caldera. The most 

extensive and productive aquifer in the region is the 

thick sequence of valley-fill deposits and interbedded 

volcanic rocks underlying the Pajarito Plateau on the 

east side of the mountain mass. The caldera contains 

both thermal and nonthermal ground water and both 

types discharge from the caldera to the southwest down 

Cafton de San Diego, which follows the trace of the 

Jemez Fault Zone. The principal geothermal reservoir, 

or aquifer, in the region is located under the central and 

western parts of the caldera.
(B)

(A)

36° 

00'

35 C 

50'

35° 

40'

1060 40'

i

106°30'

I

1060 20'

I

Baca Location No. 1

- RIO ARRIBA COUNTY

106°10'

T. 

21 

N.

20

Chino 

Mesa

R.2E.

10 MILES

10 KILOMETERS

6 R.7E. 

EXPLANATION 

FAULT

TOPOGRAPHIC RIM OF 

VALLES CALDERA AND 

TOLEDO EMBAYMENT

19

18

T.

17

N.

Valles Caldera

FEET Jemez Plateau

10,000 T

5,000-

SEA 

LEVEL

-5,000-

-10.000H

-15,000

Resurgent dome

A'

Rio Grande Rift

Ring fracture

Redondo Creek 

Graben Ring fracture Pajarito Fault Zone

METERS 

3,000

SEA 

LEVEL

--3,000

["'"'"'I

BANDELIERTUFF, RHYOLITES, AND 

CALDERA-FILL DEPOSITS

TSCHICOMA FORMATION 

PALIZA CANYON FORMATION

I ' -1 SANTA FE FORMATION, MIOCENE

MESOZOIC-PALEOZOIC ROCKS 

PRECAMBRIAN ROCKS

5 MILES

1

5 KILOMETERS

Figure 4.--(A) Geologic features in the Valles Caldera (based on Smith and others, 1970) and 

(B) generalized geologic section of the Valles Caldera (modified from Vuataz 

andGoff, 1986).

10
VALLES CALDERA

The Valles Caldera lies in the center of the Jemez 

Mountains and is one of the most prominent 

physiographic features in New Mexico. The caldera is 

approximately circular, and its topographic rim ranges 

from about 14 to 18 mi in diameter. In this report the 

Valles Caldera includes the Toledo Embayment on the 

northeast side of the caldera (fig. 4A). The caldera rim 

is breached on the southwest side at Canon de San 

Diego.

Geology

The geologic history of Valles Caldera was cited 

by Smith and Bailey (1968, p. 617-621) as a model for 

the general sequence of events in caldera and resurgent 

dome development. They distinguished seven stages of 

caldera development: (1) regional doming of an 

existing volcanic upland and the formation of ring 

fractures above the magma chamber, (2) eruption of 

ash from the ring-fracture system, (3) collapse of the 

roof of the magma chamber and subsidence of the 

circular block within the ring fractures, (4) formation 

of a lake within the caldera, accumulation of volcanic 

rocks within the caldera through additional eruptions, 

and erosion of volcanic rocks from the caldera rim, (5) 

uplift and doming of the central block, with faulting of 

this resurgent dome and extrusion of lava from the 

faults, (6) volcanic eruptions through the ring fractures 

after doming and formation of lava domes in the moat 

that separates the resurgent dome from the rim of the 

caldera, and (7) erosion and hot-spring and fumarolic 

activity. The generalized map and schematic geologic 

section in figure 4 show features associated with this 

sequence. A detailed geologic map of the Jemez 

Mountains also was prepared by Smith and others 

(1970).

The ring-fracture zone along which the Valles 

Caldera floor collapsed is about 8-10 mi in diameter 

(fig. 5). The resurgent dome as now exposed composes 

about one-fourth of the area of the caldera; its summit 

is Redondo Peak. A graben crosses the resurgent dome 

in a southwest-northeast direction and is aligned with 

the Jemez Fault Zone in the Canon de San Diego. Much 

of the moat is occupied by rhyolite domes, which form 

a ring around the resurgent dome. The ages of the dated 

rhyolite domes in the northern part of the moat range 

from about 1.0 to 0.45 Ma; the youngest volcanic 

eruptions, which occurred in the southern part of the 

moat, were as recent as 0.13 Ma (Doell and others, 

1968; Gardner and others, 1986). The remainder of the

moat forms the Valle San Antonio, Valle Toledo, and 

Valle Grande (fig. 6).

All rocks exposed in the Valles Caldera are 

volcanogenic (Smith and others, 1970). They are the 

Bandelier Tuff and caldera fill in the resurgent dome; 

Valles Rhyolite in the volcanic domes that occupy the 

moat; alluvial, lacustrine, and fan deposits of volcanicrock detritus in the remainder of the moat; and 

landslide deposits and volcanic rocks of several units 

below the rim of the caldera.

Approximately 40 intermediate to deep 

boreholes have been used to explore the subsurface 

geology of the Valles Caldera. Most have been drilled 

within and near the caldera since 1960 primarily to 

evaluate geothermal resources; they also include three 

core holes drilled for scientific research by the CSDP 

between 1984 and 1988. Because the principal 

geothermal reservoir is located under the central and 

western parts of the caldera, the geology of this part of 

the caldera has been investigated in greatest detail. 

Most exploratory holes were drilled as part of the 

Union Oil Company Baca project and are collectively 

referred to as the Baca wells (fig. 5). Nielson and Hulen 

(1984, table 1) summarized geologic logs of Baca holes 

and presented a detailed description of the subsurface 

geology of the central and western parts of the caldera; 

Wilt and Vender Harr (1986) also presented a 

description of the central and western parts of the 

caldera based on geophysical and geological data.

The stratigraphy of the Valles Caldera, as 

interpreted from drill holes, is presented in table 1. 

Precambrian granitic rocks underlie the caldera at 

depth. Overlying the Precambrian granite rocks, in 

ascending order, are the Madera Limestone, the arkosic 

Abo Formation, and the arkosic Santa Fe Group/ 

Abiquiu Tuff. Volcanic units overlie these sedimentary 

rocks. The oldest is the Paliza Canyon Formation, 

which is composed of altered andesites and dacites. 

Overlying this formation in the eastern part of the 

caldera is the Tschicoma Formation, composed of 

dacite, rhyodacite, and quartz latite (Smith and others, 

1970); in the western part of the caldera the formation 

is overlain by a sequence of tuffaceous rocks 

designated the "Lower Tuffs" by Nielson and Hulen 

(1984). The younger Bandelier Tuff, present 

throughout the Jemez Mountain area, overlies these 

units. It is greater than 6,000 ft thick in some areas of 

the caldera, but is only locally greater than 1,000 ft 

thick outside the caldera. The greater thickness within 

the caldera is attributed to simultaneous eruption of the 

tuff and collapse of the caldera (Dondanville, 1978, 

p. 157).

11
Baca Location No. 1

? HOT SPRING AND NUMBER

 GEOTHERMALBOREHOLE 

AND NUMBER-Wells with 

no letter designation are 

Baca wells

% FUMEROLE

T. 

20 

N.

19

18

R.2 E.

10 MILES 

I

R.5E.

I 

10 KILOMETERS

Figure 5.--Location of selected geothermal boreholes and hot springs in the Valles Caldera region 

(locations from Trainer, 1978; and Goff and others, 1992).

SodaDam 

Site I- - " i 

Site2___^Spj-ings

R.2 E.

10 MILES

10 KILOMETERS

4 R.5E. 

EXPLANATION

08321500

A DISCONTINUED STREAMFLOW-GAGING 

STATION AND NUMBER

Figure 6.-Principal streams in the Valles Caldera region and location of discontinued 

U.S. Geological Survey streamflow-gaging stations.

12
Quaternary Valles Rhyolite and caldera-fill 

deposits overlie the Bandelier Tuff. Alluvial, landslide, 

and lacustrine deposits form the youngest units in the 

caldera. A detailed description of rocks in the western 

half of the caldera is described in Nielson and Hulen 

(1984).

The subsurface "floor" of Valles Caldera is 

asymmetrical, and the caldera has been referred to as a 

"trapdoor" caldera (Nielson and Hulen, 1984). Depths 

to the Precambrian basement rocks range from about 

2,500 ft on the western edge, to about 10,000 ft under 

Redondo Creek, to about 15,000 ft on the east side 

(fig. 4B; Wilt and Yonder Haar, 1986). The asymmetry 

is consistent with the superposition of the caldera 

across the western edge of the older Rio Grande Rift 

(Heiken and others, 1986). Because deep holes have 

not been drilled in the eastern part of the caldera, what 

is known about the subsurface geology in this area is 

based primarily on geophysical data.

The major structural elements of Valles Caldera 

are ring faults that are associated with formation of the 

caldera and normal faults that form the Redondo Creek 

Graben, which trends northeastward across the center 

of the resurgent dome (fig. 4A). The concentrically 

arranged ring faults and associated fractures form a 

zone about 2 to 3 mi wide that lies several miles within 

the topographic rim; for the most part, the zone is 

coincident with rhyolite domes that have extruded 

within the caldera. The Redondo Creek Graben that 

cuts across the resurgent dome is formed by numerous 

normal faults that align with the older Jemez Fault 

Zone to the southwest, which suggests that structures 

within the resurgent dome are controlled by older faults 

in the Precambrian basement (Goff and Grigsby, 1982; 

Nielson and Hulen, 1984). Displacement along the 

graben is greater along the northwestern margin than 

along the southeastern margin. The high-angle faults of 

the graben and associated fractures serve as conduits 

for geothermal fluids in the caldera (Dondanville, 

1978, p. 159).

Hydrologic Setting

The principal streams draining Valles Caldera 

are San Antonio, Redondo, and Sulphur Creeks and the 

East Fork Jemez River (fig. 6). San Antonio Creek and 

the East Fork Jemez River join just outside the 

topographic rim of the caldera to form the Jemez River. 

Both San Antonio Creek and the East Fork Jemez River 

appear to be gaining streams throughout the caldera.

The base flow of streams in the caldera is from shallow, 

nonthermal ground-water systems and also, in places, 

from thermal or mineral springs. The USGS operated 

streamflow-gaging stations on Redondo Creek (station 

08319945) and Sulphur Creek (station 08319950) 

during water years 1982-85 and on the Jemez River 

directly below the confluence of the East Fork (station 

08321500) periodically during water years 1951 -90. 

Redondo Creek (12.1-mi2 drainage area) had a mean 

daily discharge of 3.15 ft3/s for water years 1983-84, 

and Sulphur Creek (38.0-mi2 drainage area) had a 

mean daily discharge of 4.17 ft3/s for the same period. 

The Jemez River below East Fork (173-mi2 drainage 

area) had a mean daily discharge of 33.2 ft3/s during 28 

years of record (water years 1950, 1959-76, 1982-90).

Vuataz and Goff (1986) analyzed tritium data for 

three streams within and two streams outside the rim of 

Valles Caldera: San Antonio, Sulphur, and Redondo 

Creeks; East Fork Jemez River near its confluence with 

San Antonio Creek; and the Jemez River upstream 

from Soda Dam (fig. 6). Because these streams drain 

small areas, the stream water clearly exhibits local and 

seasonal variations in the tritium content of 

precipitation. The tritium content of the streams in 

1982-83 varied between 6 and 39 tritium units (TU), 

which indicated that the average age of the stream 

water ranged from 0 to 5 years. The seasonal variations 

observed in the Valles Caldera streams were similar to 

seasonal variations observed in the tritium content of 

precipitation in Albuquerque (U.S. Geological Survey, 

Albuquerque, N. Mex., unpublished data).

Vuataz and Goff (1986, table 1) compiled and 

analyzed a considerable number of isotopic analyses 

for oxygen-18 ( 18O) and deuterium (2H or D) in water 

from the Jemez Mountains. From these data, they 

defined the following empirical relation, or meteoricwater line, for precipitation in the Valles Caldera area:

= 8518O+12 0)

where 8D is the deuterium content and 818O is the 

oxygen-18 content of water expressed in permil 

relative to standard mean ocean water (SMOW), the 

normal reference standard. This relation is consistent 

with the location of the region relative to the ocean. 

Vuataz and Goff (1986) also calculated the relations 

between the altitude of ground-water recharge and the 

8D and 818O content of the recharge water; the 

relations are the result of the pronounced gradient of

13
the isotopic composition of precipitation with altitude. 

For Valles Caldera the relations are:

and

E = - 147.3(8D) - 3786

= -1030(618O)-3809

(2)

(3)

where E is the altitude, in feet, of ground-water 

recharge. Equations 1-3 were used to evaluate the 

source regions and circulation paths of ground water in 

the region, which is discussed in more detail in the 

following sections.

Several types of ground water distinct in 

history, mode of occurrence, temperature, or 

geochemistry have been identified in Valles Caldera 

and the Jemez Mountains. Trainer (1974) identified 

warm and cold water of shallow circulation, acid 

sulfate water, and geothermal reservoir fluid. Goff and 

Grigsby (1982) and Vuataz and Goff (1986) expanded 

the understanding of different water types in the Valles 

Caldera. Dondanville (1971), Trainer (1975), and Goff 

and others (1981) first discussed the mineral waters 

outside the caldera as mixtures derived in part from 

reservoir fluid.

Nonthermal Ground Water

Nonthermal ground water in Valles Caldera 

occurs in diverse, perched aquifers and in deeper 

valley-fill aquifers. Although the hydrologic relation 

between the nonthermal aquifers and the geothermal 

reservoir has not been fully established, nonthermal 

water is distinguished from its thermal counterpart by 

small concentrations of chloride and trace elements, 

such as boron (Vuataz and Goff, 1986); the dominant 

anion in nonthermal water is bicarbonate. The oxygen 

and hydrogen isotopic composition of nonthermal 

ground water indicates that it is of meteoric origin 

(Vuataz and Goff, 1986).

The near-surface, nonthermal ground water of 

Valles Caldera occurs in valley-fill deposits and 

volcanic rocks of the interior domes. Volcanic rocks in 

the caldera do not contain important aquifers, but in 

places springs issue from these rocks. Small ephemeral 

seeps and springs and spring-fed streams that drain the 

unconsolidated deposits below the slopes of the caldera 

rim, resurgent dome, and volcanic domes in the moat 

indicate that these deposits are partly saturated during 

spring and early summer. Perennial springs issue from

fractured rock in the volcanic domes, particularly at the 

edges of large moat valleys, and from terrace deposits 

of alluvial deposits at the sides of large valleys. The 

porous rhyolite domes are important recharge areas for 

the volcanogenic sedimentary rocks that fill the 

caldera.

Volcanogenic sand and gravel of the intracaldera 

lake deposits form the most extensive nongeothermal 

aquifers in Valles Caldera and are found primarily in 

Valle Grande and Valle Toledo in the east and northeast 

areas of the caldera (fig. 6). Conover and others (1963) 

investigated ground-water conditions in the area in 

1949 to determine water-supply potential. The 

following summary is based primarily on their report.

The maximum thickness of sand and gravel fill in 

Valle Grande is not known; the deepest hole drilled 

(1,185 ft) did not reach the base of the valley fill. The 

maximum thickness of unconsolidated deposits in 

Valle Toledo is about 450 ft. The valley fill consists 

chiefly of volcanogenic sand and gravel, with 

intercalated beds of clay that were deposited in the 

caldera lake. The central part of each valley is 

underlain by one or more extensive clay beds; the clay 

beds are less extensive near the valley walls than in 

central parts of the valley. Ground water is confined 

beneath the clay over large areas, and where confined, 

the potentiometric surface is commonly above land 

surface. The overlying confining clay is as much as 295 

ft thick in Valle Grande and about 80 ft thick in Valle 

Toledo. Ground water generally is unconfined outside 

the margins of the clay.

In Valle Grande and Valle Toledo recharge 

occurs by infiltration of rain and snowmelt on some of 

the mountain slopes and on alluvial fans and benches 

that border the valleys. Springs issuing from the 

rhyolite domes near the margins of the valleys and 

springs that flow from the unconsolidated deposits at 

the valley margins provide recharge to the valley-fill 

aquifers.

Natural discharge of nonthermal ground water 

from Valles Caldera takes several paths, not all of 

which are fully understood. Some water obviously 

discharges through springs, especially from the higher, 

less extensive aquifers. Water from the more extensive 

principal aquifers in the valley fill also discharges as 

spring flow and seepage to the principal streams, as 

evidenced by downstream gain in discharge of valley 

streams (Conover and others, 1963). Tritium analyses 

of nonthermal springs in the caldera indicate that most 

springs issue water between 20 and 75 years old 

(Vuataz and Goff, 1986). Tritium analyses of water 

from San Antonio Creek and East Fork Jemez River

14
indicate that during some seasons these streams may 

contain more than 50 percent ground water of this age.

Some deeper discharge from the valley-fill 

aquifers recharges the underlying geothermal reservoir 

by slow leakage through relatively impermeable rocks 

and along fractures and faults (Faust and others, 1984; 

Vuataz and Goff, 1986). Purtymun and Johansen 

(1974) proposed ground-water discharge from Valles 

Caldera as the major source of recharge to the main 

aquifer under the Los Alamos area, which means that 

substantial ground-water discharge from the caldera 

must pass under the caldera rim to the east. However, 

several lines of evidence indicate that ground-water 

discharge from the caldera cannot be a substantial 

source of recharge to the main aquifer under Los 

Alamos (Fraser Goff, Los Alamos National 

Laboratory, written commun., 1993). First, if water in 

the main aquifer were recharged by ground water from 

the caldera, the stable isotopic content of ground water 

in the two areas should be similar. However, the 

deuterium and 18O content of water from cold springs 

and geothermal wells in the caldera is significantly 

different from that of water from wells and springs in 

the main aquifer near Los Alamos. Second, two major 

structural barriers to ground-water flow lie between 

Valles Caldera and the Pajarito Plateau the ringfracture zone and collapse faults of the caldera 

depression and the Pajarito Fault Zone (fig. 4A). 

According to Goff, faults of this magnitude impede the 

flow of ground water in directions normal to the fault 

plane because of the presence of fault gouge and clays, 

which create a relatively impermeable barrier within 

the fault zone.

The principal aquifer and stream in each major 

valley form a single hydraulic system according to 

Conover and others (1963). Their study showed that 

properly constructed wells in the valley fill can each 

yield more than 1,000 gallons per minute (gal/min). 

They estimated from aquifer tests that the 

transmissivity of the valley-fill aquifer is at least 3,300 

feet squared per day (ft2/d); the storage coefficient was 

not determined. The specific capacity of the pumped 

well used in the Valle Grande test was about 10 gallons 

per minute per foot (gal/min/ft) of drawdown. Aquifer 

tests in Valle Toledo showed transmissivity to be about 

6,700 f^/d and the storage coefficient to be about 

0.005. The specific capacity of the pumped well used in 

the Valle Toledo test was about 50 gal/min/ft of 

drawdown. Conover and others (1963) concluded that 

a considerable supply of ground water could be 

developed because of large volumes of water stored in

the valley fill. However, by assuming as they did that all 

ground-water discharge from the perched aquifers was 

in the form of spring flow and seepage to streams, the 

amount of water perennially available to wells as 

recharge would equal the base flow of streams in the 

valleys under nondeveloped conditions. From 

streamflow measured in 1948 and 1949, Conover and 

others (1963, p. 33-34) estimated these amounts to be 

about 750 million gallons (gal) or 2,200 acre-feet per 

year (acre-ft/yr) in Valle Grande and about 540 million 

gal or 1,600 acre-ft/yr in Valle Toledo.

Surface and Near-Surface Geothermal 

Features

The geothermal system underlying the Jemez 

Mountains, primarily in the center and western half of 

Valles Caldera, manifests itself in several forms at the 

surface, including young rhyolitic volcanic rocks, 

thermal waters, hydrothermally altered rocks, and 

elevated heat flow. These surface features guided early 

exploration for geothermal resources (Dondanville, 

1978), which began in the Sulphur Springs area (Baca 

wells 1,2, and 3; fig. 5). Thermal waters that 

discharging at the surface in the Valles Caldera are 

grouped into two types on the basis of their 

geochemistry and geohydrology: (1) thermal meteoric 

waters and (2) acid sulfate waters (Trainer, 1974; Goff 

and Grigsby, 1982; Vuataz and Goff, 1986).

Thermal Meteoric Water

Thermal meteoric water discharges from 

fractures in rhyolite and from contacts of rhyolite and 

underlying units in the ring-fracture zone of the 

western and southwestern parts of the caldera; several 

shallow wells in the southwestern section of the moat 

also have penetrated this type of water, for example 

well P-7 (fig. 5). Selected physical data for hot springs 

and a geothermal well in the Valles Caldera are 

summarized in table 2. Temperatures of thermal 

meteoric water range from 16.4 to 40.6 °C (table 2) 

compared with about 10 to 15 °C for other shallow 

ground water in the region (Vuataz and Goff, 1986, 

table 1). Chemically and isotopically, thermal meteoric 

water resembles cold ground water that has been 

conductively heated (Vuataz and Goff, 1986, p. 1840). 

More concentrated thermal water from the geothermal 

reservoir has been penetrated in deep drill holes in the 

southwestern part of the calciera and is discussed later 

in the report.

15
Table 2. Summary of selected physical data for hot springs and a geothermal well in Va

[Data from Water Resources Associates, Inc. (1977), Trainer (1978), files of the U.S. Geologi

gal/min, gallons per minute; °C, degrees Celsius; (iS/cm, microsiemens per centimeter at 25 °C

Name and identifier of well or 

spring1 (fig. 5)

McCauley Spring, H-39

Springs north of McCauley Spring, 

H-36, H-37, and H-38

Spence Springs, H-42

San Antonio Hot Springs, P-12

Group of 4 springs 0.8 mile south 

of San Antonio Spring, P-13, 

P-14, P-15, and P-16

Geothermal well, P-7

Bathhouse Spring, P-9

West San Antonio Spring, 214

Period of 

measurement

1972-74

1972-73

1972-74

1972-73

June 1973

1973-74

1972

Discharge

Number

of

measure- Range 

ments (gal/min)

17 310 - 400

27 190 - 290

6 31-46

211 160 - 320

32 21 - 35

1 70 

(Aug. 14, 1973)

1 12 

(Nov. 14, 1972)

Temperature

Number

of

measurements

18

3

4

3

4

2

1

41

Range

30.6-31.6

30.6 - 31.4 

(Sept. 29, 1972)

39.4 - 40.6

39.8-40.6

16.4-29.1 

(Oct. 4, 1972)

16.4 - 19.4

37.6 

(Nov. 14, 1972)

27 

(Oct. 15, 1971)

aSite numbers from original references; West San Antonio Spring from Water Resources Associates, Inc. (1977); all o

2Measurement in stream upstream from junction with San Antonio Creek. 

3Total discharge measured in two streams downstream from springs. 

4Data from Water Resources Associates, Inc. (1977).
The hot springs and geothermal wells represent 

two geohydrologic settings: one in which the groundwater flow field approaches the ideal assumed for flow 

through relatively homogeneous material and one in 

which flow is confined by an impervious boundary at 

the base of the aquifer. The first geohydrologic setting 

is exemplified by the Bathhouse Spring (P-9, fig. 5), 

which yields water transmitted by a fracture in rhyolite 

overlain by alluvium (Summers, 1976, p. 31). The flow 

path is visualized as a broad arc, convex downward, 

from a higher recharge area to the discharge point near 

the stream. Flow to geothermal wells in this area is 

believed to be similar except that the wells intercept the 

flow path beneath the surface and thus "short circuit" 

the latter part of the normal flow path. The second 

geohydrologic setting is exemplified by springs H-39 

and P-12 (fig. 5). Each spring is at or near the contact 

of volcanic rock and underlying Abo Formation and is 

interpreted as a contact spring that drains a perched 

aquifer. The ultimate control on locations of the springs 

is probably the topographic form of the unconformity 

between the Abo Formation and overlying volcanic 

rock, with the springs draining valleys on the Abo 

surface.

In both settings described above, geochemical 

data suggest that the thermal water is composed 

primarily of ground water that circulates in the upper 

1,500 ft of the caldera moat and is heated by the high 

upward heat flux in the area; further, the thermal water 

does not appear to be composed of hydrothermal fluids 

or a mixed water containing such fluids (Goff and 

Grigsby, 1982; Vuataz and Goff, 1986). Chemical 

analyses of thermal meteoric ground water from the 

Valles Caldera are presented in table 3; additional 

chemical data are listed in Vuataz and Goff (1986, table 

1). The thermal meteoric ground water of the caldera is 

a dilute sodium calcium bicarbonate water and is 

chemically and isotopically similar to the nonthermal 

ground water of the caldera. However, the thermal 

meteoric water generally has larger SiC>2 

concentrations than its nonthermal counterpart. The 

composition of thermal water differs from that of water 

in the underlying Abo Formation and Madera 

Limestone, indicating that the thermal water is not 

likely to have flowed through these rocks for any 

distance. Rather, the chemical composition of the 

thermal water indicates that it has been in contact with 

volcanic rock, largely or exclusively, since entering the 

ground.

The deuterium and 818O content of selected 

samples of thermal meteoric and other types of ground 

water from and near the caldera is listed in table 4; 

locations of sites listed in table 4 are shown in figures 5 

and 7. Vuataz and Goff (1986, table 1) presented 

additional isotopic analyses of thermal meteoric water. 

A plot of §D and 8 180 values of selected thermal 

meteoric water samples is shown in figure 8; other 

water types from the Jemez Mountains also are shown, 

as is the meteoric-water line for the Jemez Mountains 

region developed by Vuataz and Goff (1986, fig. 5). 

The isotopic compositions of the thermal meteoric 

ground water, which plot close to the meteoric-water 

line, indicate that this water is derived from local 

precipitation and that its isotopic composition has not 

been significantly changed by water-rock interaction or 

boiling.

The tritium content of Bathhouse Spring, San 

Antonio Hot Spring, Spence Spring, and McCauley 

Spring (P-9, P-12, H-42, and H-39, respectively, in fig. 

5) was determined by Trainer (1978, p. 127) and 

Vuataz and Goff (1986, table 1). Water samples were 

collected from the springs in March of 1973,1982, and 

1983. In 1973 and 1983, the tritium content of the four 

springs was less than 1 TU, which indicates that the 

water probably entered the ground more than 50 years 

prior to discharging at the springs. In March 1982, 

however, the tritium content of the springs was between 

2 and 8 TU, and the mineral content of the water was 

slightly smaller than that of samples collected in 1983. 

The tritium data for 1982 indicate that some post-1953 

water contributes to the flow of these thermal springs. 

When considered collectively, the isotope and 

chemical data support the idea that the thermal water 

issuing from the springs is composed primarily of 

ground water that circulates in the upper 1,500 ft of the 

caldera moat and is heated by the high conductive heat 

flux in that area (Vuataz and Goff, 1986).

Acid Sulfate Water

Acid sulfate water is characterized by low pH 

and large concentrations of sulfate and issues from 

fractures and faults on the western slope of the 

resurgent dome. The Sulphur Springs area (figs. 5 and 

9), where several major faults and fractures intersect, 

contains the largest concentration of springs that issue 

acid sulfate water. The area is also the hottest and most 

active zone of surface thermal manifestations in the 

caldera and contains thermal and nonthermal springs,

17
Table 3. Chemical analyses of thermal meteoric ground water in Valles Calde

[Concentrations in milligrams per liter; (iS/cm, microsiemens per centimeter at 25 degrees Celsius 

<, less than; site 214 analysis from Water Resources Associates, Inc. (1977); all other analyses by U.S. 

Site 

identifier 

(fig. 5)

H-39

H-42

P-7

P-9

P-12

214

Site

identifier

(fig. 5)

H-39

H-42

P-7

P-9

P-12

214

Source of 

water

Spring

Spring

Well

Spring

Spring

Spring

Lithium

-

0.69

.14

~

~

-

Date 

sampled

. 01-16-73

12-01-72

08-14-73

08-01-47

05-16-73

10-15-71

Bicarbonate

94

144

603

77

61

62.9

Specific 

conductance 

(uS/cm)

180

282

850

167

110

94

Carbonate

<1

1.0

<1

<1

<1

-

PH 

(standard Temperature 

units) (°C) Calcium Magnesiu

8.0 31.5 9 5

8.0 40.5 6 2

7.4 20.0 32 9

6.7 :38.2 6 1

7.7 40.0 5 <1

8.0 27.0 6.4 2.4

Sulfate Chloride Fluoride Boron Brom

7 4 1.0 0.02

18 12 .7 .07 0.

11 6 1.2 .64 .

15 17 1.6

9 2 .8 .04 .

<1 5

measured 11-14-72. 

2Sum of sodium and potassium expressed as sodium.
Table 4. Deuterium and oxygen-18 isotope data for wells, springs, 

and streams in the Jemez Mountains region

[°/00, permil; °C, degrees Celsius; xx, day of month not reported; --, no data 

or not applicable; LANL, Los Alamos National Laboratory]

Site 

identifier 

(figs. 5 

and 7) Sample source Date

8D

(°l v /oo') 

8180

<°/00>

Temperature 

(°C)

Altitude of 

land surface 

(feet above Refersea level) ence1

Los Alamos and Pajarito area

LA-1

LA-4

LA-5

LA-19

L-1B

L-6

LG-1

LG-1A

LG-2

LG-4

LG-6

T-2

T-3

PM-1

PM-2

Gallery Spring

Sacred Spring

Basalt Spring

White Rock Canyon Spring

Well L-1B, LANL

Well L-6, LANL

Well G-l, LANL

Well G-1A, LANL

Well G-2, LANL

Well G-4, LANL

Well G-6, LANL

Well T-2

Well T-3

Well PM-1, LANL

Well PM-2, LANL

07-24-76 

08-07-78

08-07-78

08-17-78

09-07-76

07-24-76 

09-xx-78

09-xx-78

09-xx-78

09-xx-78

09-xx-78

09-xx-78

09-xx-78

OS-xx-78

OS-xx-78

07-24-76 

09-xx-78

09-xx-78

-88.7 

-84.3

-81.8

-76.5

-76.8

-107.4 

-103.4

-94.7

-81.0

-82.5

-83.1

-76.3

-76.0

-73.5

-73.8

-76.2 

-74.1

-77.5

-12.00 

-12.20

-11.80

-10.85

-11.00

-14.30 

-14.30

-13.45

-11.65

-11.80

-11.95

-11.10

-11.25

-10.60

-10.65

-10.70 

-10.95

-11.40

11

14

15

19

30

27

29

28

30

26

31

11

13

28

24

8,000 A 

D,F

5,640 D, F

6,200 D, F

5,400 D, F

A 

D,F

D,F

D,F

D,F

D,F

D,F

D,F

F

F

A 

D,F

D,F

Sulphur Springs area

P-2 Men's Bathhouse Spring 11-30-72 

Ol-xx-79 

08-xx-81

-47.7 

-50.2 

-47.1

-2.12 

-3.25 

-3.65

78 

82

8,500 A 

F 

F

VG-21 Sulphur Creek 08-xx-81 -72.9 -9.75 16

19
Table 4. Deuterium and oxygen-18 isotope data for wells, springs, 

and streams in the Jemez Mountains region Continued

Site 

identifier 

(figs. 5 

and?) Sample source Date

8D

<°/oo)

8180

<°/00>

Temperature 

<°C)

Altitude of 

land surface 

(feet above 

sea level)

Reference1

Ring-fracture zone

H-39

H-42

P-7

P-9

P-ll

P-12

VG-34

VG-39

SAC

EF

McCauley Spring

Spence Spring

Thermal well near San Antonio

Creek

Bathhouse Spring

Cold Spring near San Antonio 

Hot Spring

San Antonio Hot Spring

Battleship Seep

Valle Grande Spring

San Antonio Creek

East Fork Jemez River

12-13-74 

07-26-76

03-XX-82

12-01-72 

07-24-76

03-xx-82

12-13-74

07-24-76

02-xx-79 

OS-xx-82

07-20-76

07-20-76 

03-xx-82

04-xx-80

03-xx-82

02-xx-79

03-xx-82

03-XX-82

-91.0 

-90.6

-89.1

-86.8 

-88.4

-86.5

-92.7

-93.5

-86.4 

-85.0

-93.2

-93.6 

-91.6

-92.7

-85.1

-92.9

-90.5

-88.0

-12.44 

-12.70

-12.45

-11.89 

-12.05

-12.25

-12.99

-12.70

-12.40 

-11.80

-12.70

-13.10 

-12.70

-12.80

-12.50

-12.85

-12.85

-12.40

-

32

-

42

_

-

38 

37

-

41

11

14

2

3

4

7,350

7,340

_

-

8,430

8,280

8,350

6,790

8,630

8,430

6,790

B

A

F

B

A

F

B

A

F 

F

C

A 

F

F

F

F

F

F

Soda Dam and Jemez Springs area

H-6

H-17

VA-5

VA-10

Soda Dam Spring

Abandoned well, Jemez Springs

Grotto Spring, Soda Dam

Main Spring, Jemez Springs

12-01-79 

Ol-xx-83

05-30-74

07-xx-78

01-04-79 

01-19-79

-84.8 

-84.0

-85.2

-84.6

-82.3 

-81.4

-10.40 

-10.35

-10.52

-10.65

-10.6 

-10.4

47

-

38

55 

36

6,330

6,330

6,200

B 

F

B

F

E 

E

VA-15 Well at Jemez Springs, at 500 feet 01-19-79 -85.9 -11.8 61 6,200

20
Table 4. Deuterium and oxygen-18 isotope data for wells, springs, 

and streams in the Jemez Mountains region Concluded

Site 

identifier 

(figs. 5 

and?)

VA-19

Sample source

Well at Jemez Springs, at 80 feet

Date

01-19-79

6D

(°l \ '00')

-84.0

8180 

(°/oo)

-11.3

Temperature 

(°C)

68

Altitude of 

land surface 

(feet above 

sea level)

6,200

Reference1

E

Redondo Creek area

RC

4

13

15

19

24

Redondo Creek

Baca 4 well

Baca 13 well

Baca 15 well

Baca 19 well

Baca 24 well

05-XX-83

06-xx-82

06-xx-82

07-xx-82

lO-xx-82

06-xx-82

-88.7

-88.3

-86.3

-83.9

-83.1

-81.8

-12.50

-9.96

-9.96

-8.61

-8.41

-8.43

4

294

278

268

223

259

8,010

-

-

~

~

~

F

F

F

F

F

F

Other areas, Jemez Mountains

H-2

N-4

N-10

VG-35

VG-38

VG-40

VG-41

Spring, Agua Durme

Well GT-2, Fenton Hill

Spring, Calaveras Canyon

Sino Spring

Indian Valley well

Las Conchas Spring

Unnamed cold spring

12-13-74

04-23-74 

ll-xx-80

12-07-72

03-xx-82

10-xx-79

08-xx-79 

05-xx-83

08-xx-79

-80.0

-78.9 

-82.6

-96.5

-87.2

-91.1

-78.2 

-79.3

-98.2

-12.05

-8.12 

-11.05

-13.14

-11.90

-12.75

-11.40 

-11.65

-13.75

~

160

~

17

18

15 

3

10

7,390

8,155

7,550

~

9,090

8,170

B

B 

F

B

F

F

F

F

References:

A U.S. Geological Survey data files.

B Trainer, 1978, p. 130.

C Trainer and Lyford, 1979, p. 300.

D Goff and Sayer, 1980, p. 6.

E Goff and others, 1981, table 2.

F Vuataz and Goff, 1986, table 1. 

Recalculated isotope values before flashing.

21
106°50' 106°30' 106°10'

36° 

00'

35° 

40'

R.8E.

on iriinMPTPBQ ' VG PREFIXINWELLORSPRING 

20 KILOMETERS IDENTIFIER INDICATES

DATA FROM VUATAZ AND 

GOFF, 1986

Figure 7.-Location of selected sampling sites for deuterium and oxygen-18 data listed in table 4.

 100

/

' -- METEORIC-WATER LINE 

/ (from Vuataz and Goff, 1986)

n

 NONTHERMAL GROUND WATER

fj STREAM WATER

0 THERMAL METEORIC GROUND WATER

A MINERALIZED THERMAL GROUND WATER \

-110 -16 -10

DELTA OXYGEN-18 (6 18O), IN PER MIL

Figure 8.-Deuterium and oxygen-18 data for selected waters inthe Jemez Mountains region.

22
Redondo Creek EAST 

Graben 

Baca-17 _ 300Q

LEVEL

POST-CALDERA 

RHYOLI T ES

0 500 1,000 FEET I ' ' i 

0 500 1,000 METERS

| | CALDERAFILL

TERTIARY 

SEDIMENTARY 

ROCKS

PALEOZOIC 

SEDIMENTARY 

ROCKS

EXPLANATION

PRECAMBRIAN GRANITE 

AND GNEISS

VAPOR-DOMINATED ZONE

LIQUID-DOMINATED 

ZONE

FAULT-Arrows show 

direction of movement

SEA 

LEVEL

>x^. DIRECTION OF

^ SHALLOW GROUNDWATER RECHARGE

300° LINE OF EQUAL TEMPERATURE--ln degrees Celsius. 

Intervals 50 and 100°

VC-2A

I

GEOTHERMAL WELL AND 

IDENTIFIER-Locatlons 

shown In figure 5

Figure 9.-Generalized section of the Sulphur Springs area, Valles Caldera 

(modified from Goff and others, 1992, fig. 7, and published with 

permission).

mud pots, fumaroles, and sublime sulfur (Goff and 

others, 1985). Hydrothermal alteration is prominent 

throughout the area and is most intense along fault 

traces. Gases also discharge in many other locations in 

the western part of the caldera as evidenced by 

perceptible levels of H2S in the air and by the rise of 

bubbles through pooled surface water, particularly in 

the canyon of Redondo Creek (Union Oil Company of 

California and Public Service Company of New 

Mexico, 1978), but gases do not discharge to the extent 

that they do at Sulphur Springs. The geology, water and 

gas chemistry, and hydrothermal alteration of the 

Sulphur Springs area are discussed in detail in Goff and 

Grigsby (1982), Goff and others (1985), Charles and 

others (1986), and Vuataz and Goff (1986); the 

following discussion draws from those investigations.

The Sulphur Springs thermal features are 

manifestations of an underlying vapor-dominated zone 

of the geothermal reservoir (the only surface 

expression in the caldera of the reservoir) derived by 

the boiling of a deeper liquid-dominated flow system 

that does not reach the surface (Dondanville, 1978, p.

158; Goff and others, 1992). Water vapor, H2S, and 

CO2 are released from the underlying boiling liquid. As 

the gases reach the surface, the H2S is oxidized to form 

SO4 , which mixes with the condensing water vapor to 

form an acid condensate, which mixes with shallow 

ground water. Gaseous springs around the periphery of 

Sulphur Springs discharge what has been termed 

carbonated meteoric water (GorTand Grigsby, 1982). A 

generalized section of the Sulphur Springs area is 

presented in figure 9. The deeper geothermal system 

beneath the Sulphur Springs area is discussed in later 

sections.

The hot springs and mud pots in the Sulphur 

Springs area have large concentrations of SO4 (greater 

than 1,000 milligrams per liter (mg/L)) and small 

concentrations of Cl (less than 10 mg/L). The pH of the 

water is between 0.6 and 5. The SiO2 concentrations of 

acid sulfate water are large (generally greater than 200 

mg/L), and concentrations of Al, Fe, Mn, Ca, and Mg 

are large relative to concentrations of Na and K. The 

water chemistry reflects the hydrothermal alteration of 

the surrounding rhyolitic host rock. Bicarbonate

23
(HCO3~) cannot exist as a major species in the water 

because of the low pH. The chemistry of the hot springs 

changes seasonally because the springs are a mixture of 

condensed steam, dissolved gases, and shallow ground 

water. Cooler types of springs are formed by lower 

temperature gases bubbling through stream water or 

pools of water. This type of water also is acidic but less 

concentrated than hotter springs because of the smaller 

proportion of condensate. A condensed steam sample 

from the main fumarole in the Sulphur Springs area 

contained sulfuric acid and NH4 as the main ionic 

species (Goffand others, 1985). Hot gases at Sulphur 

Springs are approximately 99 percent CO2 and 1 

percent H2S by volume, with minor amounts of H2, 

CH4, andNH3. Chemical and isotopic analyses of acid 

springs, condensed steam, gaseous cold springs, and 

fumarole gases are presented in Goffand others (1985, 

tables 2-4) and Vuataz and Goff (1986, table 1). The 

composition of the gases resembles that of gases from 

other high-temperature geothermal systems elsewhere 

in the world (Goffand others, 1985).

The 6D and 818O content of the acid sulfate 

water in the Sulphur Springs area varies greatly. Vuataz 

and Goff (1986) attributed most of this variation to the 

processes of subsurface boiling and surface 

evaporation. They also attributed the 818O-depleted 

water that issues from one relatively cool spring to 

isotopic exchange between the spring water and the 

CO2 that vigorously passes through it.

The tritium content of acid sulfate springs is 

variable because spring water is generally a mixture of 

condensed steam and shallow ground water. The Men's 

Bathhouse Spring or mud pot (P-2, fig. 7) in the 

Sulphur Springs area, for example, is composed 

primarily of condensed steam and contains 2.1 TU, 

whereas the Women's Bathhouse Spring (P-3, fig. 7) 

contains a higher proportion of shallow ground water 

and 19 TU. The smaller tritium content of some surface 

hot springs, when considered with tritium data for the 

deep geothermal reservoir (discussed later), indicates 

that condensed steam is produced from water at least 

50 years old (Goffand others, 1985).

(fig. 10A) and are characterized by large amounts of 

kaolinite (Dondanville, 1978, p. 158). Hydrothermal 

alteration in the caldera has been investigated in detail 

by Lambert and Epstein (1980), Charles and others 

(1986), and Hulen and Nielson (1986). The altered area 

includes the upstream half of Redondo Creek Canyon 

and a similar tract across the drainage divide to the 

northeast and a tract that surrounds Sulphur Springs 

and extends into side canyons nearby. The altered area 

along Redondo Creek is in the Redondo Creek Graben 

of the resurgent dome and that surrounding Sulphur 

Springs is in a grabenlike structure bounded by at least 

three faults. Zones of alteration at the surface in these 

areas help delineate permeable channels where vapors 

rise to the surface; based on the zones of most intense 

alteration, such channels may be confined to fault 

traces and subsidiary fractures. Isotopic analyses of the 

hydrothermally altered rocks indicate the alteration to 

be a product of meteorically derived fluids (Lambert 

and Epstein, 1980; Goffand others, 1992).

Thermal fluids of active geothermal systems 

alter the rocks with which they come into contact. 

Typically acidic water and gases react with primary 

rock-forming silicate minerals to form clays. In the 

western part of Valles Caldera, hydrothermally altered 

rocks are distributed over about a 15-mi2 area

High rates of near-surface heat flow and high 

subsurface temperatures characterize the western half 

of Valles Caldera and adjacent parts of the Jemez 

Plateau to the west. Heat flow in this region exceeds 3 

heat flow units (HFU) and is as high as 6 HFU over the 

Redondo Creek Graben and 15 HFU where discharge 

from the geothermal reservoir passes under the caldera 

rim (Reiter and others, 1976; Goffand others, 1988). 

The total heat discharge for the Valles Caldera, 

estimated by Sorey (1985) to be 18 x 106 calories per 

second (cal/s), suggests a shallow heat source, 

probably a cooling magma chamber, located beneath 

the western part of the Valles Caldera. Hulen and 

Nielson (1986) estimated the depth to the top of the 

magma body to be about 16,000 ft. Temperature 

gradients measured in wells outside Valles Caldera 

suggest that heat flow increases markedly as the rim of 

the caldera is approached from the west (Reiter and 

others, 1976), and temperature gradients within the 

caldera are markedly greater than those outside the 

caldera rim. Shallow temperature gradients within the 

caldera are presented in figure 10B. Temperature 

gradients exceed 25 °F per 100 ft in several locations 

within the caldera (Swanberg, 1983, fig. 7). The 

contours show a sharp decrease in temperature to the 

east and southeast within the caldera. Bodvarsson and 

others (1982) suggested that the sharp decrease in 

temperature gradients between Redondo Creek and
106°40'

36° 

00'

35° 

50'

A

106°30'

I

_RIO_ ARRIBA_COUNJY 

SANDOVAL COUNTY"

VALUES CALDERA

AREAL EXTENT OF 

GEOTHERMAL 

RESERVOIR 

(Bodvarsson 

and others, 

1982, fig. 1) Fenton

Hill 

site

SULPHUR. 

SPRINGS

AREA OF 

HYDROTHERMALX

ALTERATION \ 

(from Dondanvllle, 

1978, fig. 2)

L ,_

T. 

21 

N.

20

19

18

T.

17

N.

R.2E. R.5E.

106°40' 106°30'

36° 

00'

35° 

50'

RIO ARRIBA COUNTY . . Baca Location No. 1

SANDOVALCOUNTY

5«-/ \4/»fo/i/o

VALLES CALDERA

RING

FRACTURE 

\ ZONE SULPHUR 

SPRINGS

RedondoCreelo. ^* 7.5 

Graben : /

Redondo , Peak 7 - 5

5°

s

T. 

21 

N.

20

19

18

EXPLANATION

" - " " FAULT-Barand 

ball on downthrown side

7 5°___ LINE OF EQUAL 

TEMPERATURE 

GRADIENT--ln 

degrees Fahrenheit. 

Intervals 2.5 and 5.0 ° 

per 100 feet. Depths 

150-250 feet

NOTE: CONTOURS FROM

BODVARSSON AND 

OTHERS, 1982, FIG.1

T. 

17 N. '

R.2E. R.5E. 

10 MILES

I 

10 KILOMETERS

Figure 10.--(A) Areal extent of hydrothermal alteration and the geothermal reservoir and 

(B) shallow temperature gradients in the Valles Caldera.

25
Redondo Peak probably results from the presence of a 

permeability barrier in this area or from an inflow of 

colder ground water from the southeast into the 

underlying hotter geothermal reservoir. Areas of low, 

near-surface temperature gradients include Valle 

Grande and perhaps Valle Toledo, where cool ground 

water flowing through thick valley fill likely transports 

away much of the heat that is transferred upward by 

conduction through the underlying rock.

The area of high temperature gradients 

encompasses the area of active hydrothermal alteration 

(figs. 10A, B), as defined by Dondanville (1978, p. 

158), which probably reflects convective transport of 

heat to the surface by rising vapor. High temperature 

gradients elsewhere in the western part of the caldera 

also probably reflect convective transport of heat by 

rising geothermal fluids. Measurements in LANL well 

GT-2 (Pettitt, 1975a) just outside the west rim of the 

caldera (fig. 5) indicate thermal gradients in the 

basement rocks that are markedly less than those in the 

overlying section of sedimentary rocks in which most 

ground-water flow occurs. These observations are 

consistent with the convective transport of heat by 

ground water, in this case laterally out of the caldera, 

which is discussed in more detail later in the report.

Geothermal Reservoir

The current understanding of the Valles Caldera 

geothermal reservoir has developed from geothermal 

exploration conducted in the caldera between 1970 and 

1982 and other investigations in and around the 

caldera, such as the CSDP, which drilled the three deep 

holes into the geothermal system between 1984 and 

1988. The general configuration of the geothermal 

system was summarized by Goffand others (1992) and 

is illustrated in figure 11. In the geothermal system, 

meteorically derived water moves downward from the 

aquifers in the caldera fill and recharges the geothermal 

reservoir in intracaldera tuffs and precaldera rocks at 

depths of 6,500 ft or more and at temperatures reaching 

330 °C. The geothermal water then rises convectively 

to depths of 2,000 ft or less. A vapor zone (or zones) 

containing steam, CC>2, and other gases has formed 

above parts of the geothermal saturated zone. In the 

Sulphur Springs area, acid springs, fumaroles, and mud 

pots are at the top of the vapor zone and a zone of 

condensation, about 15 ft thick, exists at the surface 

(Goffand others, 1992, p. 185). The heated water of the 

geothermal system flows out the caldera to the west and

southwest under the Jemez Plateau and along the 

Jemez Fault Zone and in the semipermeable Paleozoic 

rocks that border the fault zone. This geothermal water 

mixes with other ground water as it flows along the 

fault zone, and some of this mixed or derivative water 

issues as hot springs in Canon de San Diego. Drilling 

has identified two subsystems, the Redondo Creek 

subsystem and the Sulphur Creek subsystem (Goffand 

others, 1992). These and other complexities of the 

geothermal system are discussed in following sections.

Geometry and Hydrologic Properties

The permeability, stratigraphy, structure, and 

other aspects of the geothermal reservoir have been 

investigated with geologic mapping, drilling of test 

holes, mapping of geothermal gradients, and the use of 

other geophysical techniques; results of these 

investigations are presented in Bodvarsson and others 

(1982), Garg and Riney (1982), Hulen (1982), and 

Grant and others (1984). Because the Redondo Creek 

subsystem exhibits the greatest promise for geothermal 

development, it has been more extensively studied than 

other parts of the system.

The permeability of the Redondo Creek 

geothermal subsystem is controlled mainly by 

stratigraphy and fault-related structures. The 

permeable horizons, evidenced by entry points of 

thermal fluids in the Baca wells, were identified by 

Hulen (1982, fig. 4) and Grant and others (1984, figs. 

16-18). Hulen (1982) concluded that the most 

transmissive stratigraphic horizons occur in tuffaceous 

sandstones and nonwelded tuff units scattered 

throughout the Bandelier Tuff; however, the interstitial 

permeability of the welded Bandelier Tuff is small. 

Permeable units are not continuous throughout the 

entire Redondo Creek area, but some can be correlated 

between drill holes. The thickness of permeable units 

intersected by any given well in the Redondo Creek 

area amounts to no more than 8 percent of total 

formation thickness on average (Hulen, 1982, p. 11). 

Grant and others (1984) performed a detailed analysis 

of borehole geophysical data for wells drilled in the 

Redondo Creek area and concluded that at least two 

main transmissive zones exist in the area. The deeper 

transmissive zone, which is about 500 ft thick, was 

placed between the Bandelier Tuff and the underlying 

Paliza Canyon Formation; this zone may correspond to 

the sequence of units informally designated the "Lower

26
sw

ALTITUDE 

(feet)

10,000

8,000.

6,000

4,000 

2,000 

SEA 

LEVEL

-2,000

SOUTHWEST MOAT

Canon de EAST FORK 

JEMEZ RIVER

RESURGENT DOME

BACA-4

San Diego 

JEMEZSPRINGS

NE

ALTITUDE 

(meters)

.3,000

 2,500

 2,000

. 1,500

. 1,000

 500

SEA 

LEVEL

 -500

0 1 MILE 

0 1 KILOMETER

EXPLANATION

[frlj Qv MOATVOLCANICS

ESa Qb CALDERA FILL AND 

«=3 TUFFS

n

Tu TERTIARY VOLCANIC ROCKS 

AND SEDIMENTS

tgjgg Pu PALEOZOIC ROCKS 

F\*I pGu PRECAMBRIAN ROCKS

<<= RECHARGE

200^- LINE OF EQUALTEMPERATURE--ln 

degrees Celsius. Interval 50°

GEOTHERMAL WELL-Locations 

shown in figure 5

FLOW PATH OF 

GEOTHERMAL FLUID

FAULT-Arrows show 

direction of movement

Figure 11 .-Generalized section of southwestern Valles Caldera and upper Canon de San Diego 

showing the active geothermal system (modified from Goff and others, 1992, fig. 6, 

and published with permission).

27
Tuffs" by Nielson and Hulen (1984). The upper 

transmissive zone, which is generally more productive 

than the lower zone, is within the Bandelier Tuff and 

may actually consist of two separate zones, at about 

4,900 and 5,900 ft above sea level, respectively, in a 

region that has an average land-surface altitude of 

about 9,000 ft (Grant and others, 1984).

Garg and Riney (1982, p. 31) concluded that 

most of the permeability in the geothermal reservoir 

occurs as secondary permeability primarily in the fault 

and fracture network. The structural permeability in the 

Redondo Creek area occurs primarily along the highangle, northeast-trending, normal faults that form the 

Redondo Creek Graben (figs. 4A, B) and along 

fractures associated with these faults (Hulen, 1982). 

The permeable fluid channels are marked by zones of 

hydrothermal alteration, indicating that the Redondo 

Creek geothermal subsystem has developed mostly or 

entirely under water-dominated conditions as opposed 

to vapor-dominated conditions (Hulen and Nielson, 

1986).

The Sulphur Springs geothermal subsystem of 

the geothermal reservoir is not as well defined as the 

Redondo Creek subsystem because fewer holes have 

been drilled in this area. The alignment of 

hydrothermal alteration and other geothermal features 

along fault traces indicates that faults and related 

structures control the flow of thermal fluids in both the 

Redondo Creek and Sulphur Springs geothermal 

subsystems (Goff and others, 1985). Both areas are 

bounded by high-angle faults that trend northnortheast. CSDP holes VC-2A and VC-2B in the 

Sulphur Springs area (fig. 5) reveal a vapor-dominated 

zone, about 790 ft thick, overlying a liquid-dominated 

zone; the two zones are separated by about 800 ft of 

sealed caldera-fill rocks (Goff and others, 1992). The 

liquid-dominated zone consists of stacked 

hydrothermal aquifers. Most fluid in this zone 

circulates in the caldera-fill sequence of tuffs, the 

sandstones of the Santa Fe Group that immediately 

underlie the tuff, and the deeper Precambrian quartz 

monzonite that is separated from the Santa Fe Group by 

a 2,500-ft thickness of Paleozoic rocks.

The Sulphur Springs subsystem may be isolated 

structurally from the Redondo Creek subsystem (Goff 

and others, 1985, fig. 9). Moreover, differences in the 

chemical and isotopic compositions of water samples 

collected from deep wells in each area (discussed in the 

following section) suggest two separate (or poorly 

connected) hydrothermal subsystems within the

caldera. Chemical and thermal evidence also indicate 

that each subsystem has its own zone of upflow and 

lateral outflow of thermal water: outflow from the 

Redondo Creek subsystem flowing beneath the 

southwestern rim of the caldera and Canon de San 

Diego and outflow from the Sulphur Springs subsystem 

flowing westward beneath the Jemez Plateau (Goff and 

others, 1985).

The internal geometry of the Valles Caldera 

geothermal reservoir is detailed and complex. 

Interlayering of rocks with vastly different 

permeabilities that are intersected by steeply dipping 

faults divides the reservoir horizontally and vertically 

into blocks. Thus, the more highly permeable 

stratigraphic and structural features of the geothermal 

reservoir remain interconnected, but in an 

undetermined way. Faust and others (1984) assumed 

for purposes of modeling the reservoir that, at the scale 

of the caldera, the complex interconnection of highly 

permeable features can be considered equivalent to a 

porous medium. The performance of an individual 

well, however, depends to a large degree on the faults, 

joints, and stratigraphic units that the well intersects 

and the interconnection of those faults and joints with 

other permeable structures and stratigraphic units 

(Garg and Riney, 1982, p. 31). The lack of interference 

effects among some pairs of pumping and observation 

wells during production tests suggests effective 

hydraulic isolation along some subsystem, or block, 

boundaries.

Thus far, drilling has defined only a portion of 

the Valles Caldera geothermal reservoir. Consequently, 

estimates of the areal extent and thickness of the 

reservoir can be inferred only from geologic and 

geophysical data. Several workers in the late 1970's 

(cited in Faust and others, 1984) estimated the areal 

extent of the reservoir to be about 60 to 66 mi2, which 

is approximately equal to the area encircled by the ringfracture zone of the caldera. More recent work, 

however, indicates that these estimates are 

unreasonably large and that the geothermal reservoir is 

much smaller than the caldera. Bodvarsson and others 

(1982) estimated the areal extent of the reservoir to be 

about 15 mi2, and placed the western limit of the 

reservoir at the western edge of the ring-fracture zone 

of the caldera (fig. 10). Wilt and Yonder Haar (1986), 

for purposes of reservoir simulation, made three 

estimates of the areal extent of the reservoir based on

28
geophysical and drill-hole data and on different sets of 

assumptions. The values ranged from about 8.6 to 11.6 

mi2 depending on how far the reservoir was assumed to 

extend northeast of the Redondo Creek area and 

whether the Sulphur Creek area was included in the 

reservoir. (As noted above, the CSDP identified a 

saturated zone below Sulphur Creek, so the largest 

estimate of Wilt and Yonder Haar (1986) is probably a 

more realistic value.) Faust and others (1984), when 

developing a simulation model of the geothermal 

system, initially used an area of 15 mi2, the same as that 

of Bodvarsson and others (1982). However, in the final 

model of Faust and others (1984), the areal extent of the 

reservoir was reduced to only 12 mi2 .

Thickness

Estimates of the thickness of the geothermal 

reservoir also have differed among investigators. The 

top of the reservoir is thought by most investigators to 

be the bottom of a small-permeability "caprock" 

formed within the Quaternary Bandelier Tuff as a 

product of hydrothermal alteration (Bodvarsson and 

others, 1982; Grant and others, 1984; Wilt and Yonder 

Haar, 1986). The bottom of the caprock, or top of the 

reservoir, in the Redondo Creek area is about 6,000 to 

7,000 ft above sea level or about 2,000 to 3,000 ft 

below land surface. The caprock extends above much 

of the reservoir, but its lateral extent has not been fully 

defined by drilling. The presence of fumaroles 

indicates that the caprock does not form a perfect seal 

and that leaks exist at least along fault zones. The 

bottom of the reservoir is more difficult to define. 

Nearly all fluid production in exploratory wells is 

produced from fractures or thin beds in the Bandelier 

Tuff below the caprock, a zone generally less than 

4,000 ft thick in the Redondo Creek area (Grant and 

others, 1984). No substantial production of geothermal 

fluids in drill holes has been found below the Tertiary 

Paliza Canyon Formation (table 1). However, deeper 

permeable zones exist below the Paliza Canyon 

Formation as evidenced by wells that do not produce 

geothermal fluids but accept high injection rates of 

fluids (Garg and Riney, 1982, p. 35). Bodvarsson and 

others (1982) defined the bottom of the reservoir as the 

bottom of the Bandelier Tuff and estimated the average 

reservoir thickness to be 2,000 ft, relatively thin 

compared with other estimates. Union Oil Company 

estimated an average reservoir thickness of 3,000 ft 

based on their analysis of reservoir tests (Faust and 

others, 1984). Wilt and Yonder Haar (1986) placed the

bottom of the reservoir at the bottom of the Paliza 

Canyon Formation and suggested that the reservoir 

thickens to the southeast; they estimated the thickness 

of the reservoir in the Redondo Creek area to range 

from about 2,500 to 5,000 ft. Faust and others (1984) 

placed the bottom of the reservoir at the contact with 

the basement Precambrian granite, making the 

reservoir about 6,000 ft thick, which they recognized as 

an optimistic assumption.

Temperature and Pressure Distributions

Temperature and pressure also vary from well to 

well and with depth and time of measurement. 

Estimates of the temperature distribution in the 

reservoir under the Redondo Creek area are presented 

in Grant and others (1984). Reservoir temperatures 

measured in the Baca wells range from about 225 °C, 

just below the caprock to about 330 °C in Baca well 11 

at a depth of about 6,690 ft, which corresponds to an 

altitude of about 2,380 ft. Temperature profiles of the 

deep wells are characterized by convex-upward 

inflections that separate higher gradients (about 0.089 

°C/ft) near the surface from lower gradients (about 

0.012 °C/ft) at greater depths (fig. 12). The higher 

gradients are indicative of conductive heat transfer in 

the smaller permeability caprock; the lower 

temperature gradients, which occur below about 7,500 

ft in altitude, are indicative of a convective system of 

circulating hydrothermal fluids (White, 1986). 

Reservoir temperatures estimated using chemical 

geothermometers range between 250 and 300 °C 

(Truesdell and Janik, 1986; White, 1986), in general 

agreement with measured temperatures. Maximum 

reservoir temperatures measured in Baca wells in the 

Sulphur Creek area were lower than those measured in 

wells in the Redondo Creek area and ranged between 

157 and 283 °C (GofTand others, 1985, table 1).

In the Redondo Creek area, pressures measured 

in the production zones of the Baca wells ranged 

between 450 and 1,850 pounds per square inch (lb/in2) 

(Garg and Riney, 1982, table 4). The highest pressure 

recorded was 1,850 lb/in2 at an altitude of 3,102 ft in 

Baca well 11. Grant and others (1984) analyzed 

pressure data for the Redondo Creek area and drew the 

following conclusions. Reservoir pressure, when 

plotted against altitude, defines a straight line with a 

slope of about 0.349 pound per square inch per foot 

(Ib/in2/ft), which corresponds to a hydrostatic gradient 

for a temperature of about 260 °C. The close 

correlation between pressure and altitude in the

29
10,000

ZONE OF

CONDUCTIVE

HEATTRANSFER

Approximate base of caprock

ZONEOFCONVECTIVE 

HEATTRANSFER

2,000

100 200 

TEMPERATURE, IN DEGREES CELSIUS

300

Figure 12.-Temperature profile of seven Baca wells (modified from White, 1986, fig. 3).

Redondo Creek area indicates that the subsystem is 

hydraulically connected and possibly that the upflow of 

fluids occurs in regions where the temperature exceeds 

260 °C. Reservoir pressure extrapolates to atmospheric 

pressure at about 7,875 ft in altitude, which is 

considered to be the nominal piezometric surface of the 

reservoir in the Redondo Creek area. Pressures 

measured in Baca wells in the Sulphur Creek area 

ranged from 75 to 1,400 lb/in2 (Goffand others, 1985, 

table 1).

Hydraulic Properties

Selected reservoir properties, such as the 

permeability, thickness, temperature, and pressure 

measured in Baca wells, have been summarized by 

Garg and Riney (1982, table 4) and GofTand others 

(1985, table 1) and also are discussed in Union Oil 

Company reports. Grant and others (1984) conducted a

detailed analysis of properties of selected Baca wells in 

the Redondo Creek area. Because the permeability of 

the reservoir is not uniform but rather is highly variable 

among stratigraphic units and largely controlled by 

fractures, hydrologic properties can vary significantly 

from well to well, and values determined for an 

individual well are not necessarily representative of the 

reservoir in general. For example, in the Redondo 

Creek area, the permeability-thickness product (kH) 

reported for selected Baca wells ranged between 2,600 

and 23,800 millidarcy-ft (mdarcy-ft) (Garg and Riney, 

1982, table 4). Because of such variability, Grant and 

others (1984, p. 1413) concluded that there is little 

basis on which to assign a kH value representative of 

the entire geothermal reservoir.

Representative values of physical and hydrologic 

properties have been estimated for the geothermal 

reservoir, despite the large variability from well to well. 

These values have been estimated from reservoir30
testing, stream-depletion, and geothermal-production 

analyses. For example, a 1975-76 fieldwide pressure 

interference test in the Redondo Creek area to evaluate 

the hydraulic connectivity of fractures yielded a 

permeability-thickness product of about 6,000 

mdarcy-ft (Garg and Riney, 1982, p. 34). Reservoir 

properties estimated by Bodvarsson and others (1982), 

Union Geothermal Company of New Mexico (1981), 

and Faust and others (1983, 1984) for the purpose of 

developing numerical simulation models of the 

reservoir are presented in table 5; each set of values was 

developed for a different type of model. Faust and 

others (1983) provided a detailed listing of the 

hydrologic and thermal parameters used to develop a 

calibrated three-dimensional, finite-difference model 

of the geothermal reservoir and adjoining aquifer.

Union Oil reanalyzed all well-test data in 1982 and 

revised their 1981 estimated values of average 

permeability thickness and porosity thickness to 4,000 

mdarcy-ft and 150 ft, respectively (Faust and others, 

1984, p. 605). Faust and others (1984) estimated 

horizontal permeability to be greater than vertical 

permeability by about a 4 to 1 ratio; Union Oil, 

however, assumed the horizontal permeability to be 

half the vertical permeability. Faust and others (1983, 

1984) compared and contrasted estimated properties 

presented by different workers. All estimated values of 

the permeability-thickness product of the Valles 

Caldera geothermal reservoir are smaller than those of 

other geothermal fields, which range from 20,000 to 

more than 100,000 mdarcy-ft (Garg and Riney, 1982, 

p. 34).

Table 5. Estimated reservoir properties of the Valles Caldera geothermal 

reservoir used in numerical simulation models of the reservoir

[°C, degrees Celsius; --, no data; cm, centimeter]

Property (unit of measurement)

Area (square miles)

Average thickness (feet)

Temperature (degrees Celsius)

Pressure (pounds per square inch)

Porosity (unitless)

Porosity thickness (feet)

Permeability

Horizontal (millidarcy)

Vertical (millidarcy)

Permeability thickness (millidarcy-foot)

Rock density (grams per cubic centimeter)

Rock compressibility (square centimeter/dyne)

Thermal conductivity (ergs /second cm °C)

Rock heat capacity (ergs /gram °C)

Bodvarsson 

and others 

(1982)

15.4

2,000

300

1,600

0.05

100

3.0

~

6,000

2.65

-

2xl05

9.5 x 106

Union 

Geothermal 

Company of 

New Mexico 

(1981)

60

3,000

a300

1,200

0.03

90

2.0

4.0

6,000

~

7.25 x 10'11

1.44 xlO5

-

Faust and 

others 

(1983, 1984)

16

6,000

2220-295

2520-1,880

0.03

180

3.0

0.075 - 0.75

18,000

2.65

7.25 x 10'11

1.44 xlO5

9.5 x 106

1Maximum temperature. 

2Range, increasing with depth.

31
Bodvarsson and others (1982) estimated the 

capacity of the geothermal reservoir to be 2.2 x 10 12 

pounds (Ib) of geothermal fluid in place, based on an 

area of about 15.4 mi2, a porosity-thickness product of 

about 100 ft, and a fluid density of 51.5 pounds per 

cubic feet (Ib/ft ), which corresponds to a temperature 

of 230 °C. Union Oil Company estimated the reservoir 

capacity to be about 4.7 x 10 12 Ib of geothermal fluid in 

place based on two methods of analysis, a depletion 

equation and an interference test, and a reservoir area 

of about 43 mi2 . The close agreement between the two 

estimated capacities would appear fortuitous, given the 

large differences in estimated reservoir area on which 

the capacities are based (Bodvarsson and others, 1982).

Vapor- or steam-dominated zones above the 

liquid-dominated zones have been penetrated in wells 

drilled in both the Redondo Creek and Sulphur Creek 

areas. Vapor-dominated conditions, in which steam is 

the pressure-controlling fluid phase and the vertical 

pressure profile is close to vapor-static rather than 

hydrostatic, may also exist in zones where existing 

well-pressure measurements are inadequate to 

delineate such conditions. This type of vapordominated zone develops from the upflow of steam 

from an underlying region of boiling liquid. The 

development of vapor-dominated conditions may be 

related to the depressurizing that accompanied the 

breaching of the southwestern caldera rim and draining 

of the caldera lake approximately 0.5 Ma (Trainer, 

1984; Goff and others, 1992). Following this event, 

liquid levels dropped about 1,000 ft below land surface. 

The lateral extent of vapor-dominated zones is not well 

defined, and not every well has penetrated such zones. 

The vertical extent of vapor-dominated zones is partly 

determined by the variable CO2 content of the 

hydrothermal fluid. The presence of dissolved CO2 

extends the range of temperatures and depth over 

which boiling can occur. The interface between the 

bottom of the vapor-dominated zone and the top of the 

liquid-dominated zone is not necessarily explicit (Goff 

and others, 1992). For example, Grant and others 

(1984, p. 1412) estimated the bottom of the two-phase 

zone (top of the liquid-dominated zone) in the hotter 

part of the Redondo Creek subsystem to extend 

downward to a depth of 4,100 ft (altitude of 

approximately 4,900 ft) where temperatures are near 

250 °C. More recent estimates (Goff and others, 1992, 

p. 193) place the top of the liquid-dominated zone at 

depths of 1,650 to 1,970 ft and temperatures of 

approximately 200 °C (fig. 9).

Geochemistry of Geothermal Fluids

The chemical and isotopic composition of fluids 

in the geothermal reservoir is primarily determined by 

the composition of the source fluids and the chemical 

interaction between reservoir fluids and reservoir rock. 

Evaporation associated with boiling can also affect the 

composition of water in the geothermal reservoir. The 

composition of reservoir fluids is useful in interpreting 

the source and movement of reservoir fluids and in 

estimating reservoir properties. The composition of 

reservoir fluids in the Valles Caldera is discussed in 

Delany and Truesdell (1982), Goff and others (1985), 

Truesdell and Janik (1986), Vuataz and Goff (1986), 

White (1986), and Goff and others (1992); a summary 

of those findings is presented here. Most geochemical 

data on reservoir fluids comes from samples collected 

from Baca wells in the Redondo Creek area during the 

1970's and early 1980's. More recently, geochemical 

data have been obtained for the CSDP wells. Problems 

associated with the collection of samples and 

interpretation of analyses of geothermal fluids, such as 

those caused by local boiling in the reservoir around 

the well bore, are discussed by Truesdell and Janik 

(1986) and White (1986). Other investigators report 

concentrations of constituents in the reservoir fluids 

differently; for example, some investigators report 

concentration on a total-fluid basis, which adjusts 

measured concentrations for steam loss, and others 

report concentrations on an "as-analyzed" basis. Thus, 

direct comparisons of data are not always readily 

possible, and concentrations reported may not actually 

represent the chemistry of the fluid in the reservoir.

Water in the geothermal reservoir has 

geochemical characteristics that distinguish it from 

other thermal water in the caldera. In general, the 

reservoir below Sulphur Springs and Redondo Creek 

contains a near-neutral, chloride-type water containing 

about 7,000 mg/L dissolved solids and anomalously 

large concentrations of As, B, Br, Cs, Li, Rb, and other 

trace elements (Goff and others, 1992). Geochemical 

differences distinguish water in the Redondo Creek 

subsystem from that in the Sulphur Springs subsystem.

Concentrations of major and trace constituents in 

fluid samples collected between 1973 and 1982 from 

10 Baca wells in the Redondo Creek area were 

summarized by White (1986, table 1); multiple 

samples were ana 1 -'zed from most wells. 

Concentrations ot constituents, expressed in 

milligrams per liter on a total produced fluid basis, are 

in the following ranges for most wells: SiO2, 200 to 

600; Na, 900 to 1,500; K, 150 to 250; Ca, 3 to 25; Mg,

32
less than 1.0; Cl, 1,500 to 2,500; SO4,20 to 50; HCO3 , 

20 to 160; As, 1 to 4; B, 10 to 22; Br, 3.5 to 8; F, 2.5 to 

7.5; and Li, 10 to 20. The range of constituent 

concentrations in reservoir fluids based on multiple 

samples collected from five Baca wells in 1982 is 

illustrated in figure 13. The pH of geothermal reservoir 

water measured in the field was about 7.2 (Goff and 

Grigsby, 1982); the calculated pH of reservoir water 

was 5.57 to 6.41, with a mean pH of 5.9 (White, 1986). 

Samples of reservoir fluid from the Sulphur Springs 

subsystem contain slightly larger concentrations of 

dissolved minerals than the fluid from the Redondo 

Creek subsystem (Goffand others, 1992). The 

composition of water from Precambrian rocks at the 

bottom of CSDP hole VC-2B (fig. 5) in the Sulphur 

Springs area suggests that this water is derived from a 

mix of geothermal reservoir fluid and saline pore fluid, 

which has been sampled in Precambrian rocks at the 

Fenton Hill site (fig. 5) on the flank of the caldera west 

of Sulphur Springs (Goffand others, 1992).

Although no thermal springs in the caldera have 

water chemistry that resembles that of the deep 

geothermal fluids sampled from wells, the thermal 

springs at Soda Dam and Jemez Springs in Canon de 

San Diego (fig. 5) have geochemical characteristics 

similar to the deep geothermal fluids within the caldera. 

Water issuing from these springs is a mixture of water 

from the lateral, subsurface flow of reservoir fluids to 

the southwest along the Jemez Fault Zone and local, 

dilute ground water (Trainer, 1974; Goffand others, 

1992); this derivative of reservoir fluids is discussed 

later in the report.

The dissolved mineral content of water in the 

geothermal reservoir is similar to volcanic geothermal 

water from other areas, and concentrations of dissolved 

constituents reflect interaction with reservoir rocks 

(Truesdell and Janik, 1986). White (1986) concluded 

that geothermal fluids within the Valles Caldera are in 

general chemical equilibrium with secondary minerals 

of the geothermal reservoir, which suggests stable 

temperatures during development of the geothermal 

reservoir.

The gas content of the geothermal fluids also is 

typical of volcanic geothermal systems. Reservoir fluid 

has an incondensible gas content (principally CC^) of 

about 0.4 to 1.5 percent (mean about 0.8 percent) by 

mass (Grant and others, 1984), and CO2 composes 

more than 98 mole percent of the incondensible gases 

(Truesdell and Janik, 1986). Other gases, in order of 

decreasing abundance, are: H2S, N2 H2, CH4, NH3 , Ar, 

He, and other noble gases. Concentrations of the

principal gases in fluids from the Baca wells are 

discussed in Truesdell and Janik (1986, tables 4 and 5) 

and White (1986, table 2). Smith and Kennedy (1985) 

presented the elemental and isotopic composition of 

noble gases from the geothermal reservoir and on the 

basis of these data identified two compositions of fluid 

in the Redondo Creek subsystem. All gases in the 

reservoir, with the exception of He, probably originate 

from (1) atmospheric gases dissolved in recharge, (2) 

thermal metamorphism of nearby carbonate rocks, and 

(3) other chemical reactions in the reservoir (Truesdell 

and Janik, 1986). The high 3He/4He ratios in reservoir 

gases indicate helium derived from the mantle and 

possibly the presence of a magmatic source below the 

caldera floor (Smith and Kennedy, 1985; Goffand 

others, 1992).

Isotope data (Trainer, 1978, table 8c; Truesdell 

and Janik, 1986, table 3; Vuataz and Goff, 1986, table 

1; White, 1986, table 3; and Goffand others, 1992, 

table 1) indicate a meteoric origin of the fluids in the 

geothermal reservoir and 18O enrichment of 

geothermal fluid relative to the meteoric-water line for 

the Jemez Mountains region (fig. 14). The amount of 

enrichment is typical of that measured in other 

geothermal systems and was attributed by Vuataz and 

Goff (1986) to oxygen exchange between isotopically 

heavier reservoir rocks and isotopically lighter water. 

Other processes that modify the isotopic composition 

of fluids in geothermal systems include mixing of 

nonthermal and thermal water; boiling in the upper part 

of the reservoir; and isotopic exchange between water 

and gases such as CO2- The isotopic composition of 

oxygen in reservoir fluids differs among the Baca 

wells. In general, these isotopic differences are 

attributed to different recharge source areas for the 

fluid and to the degree of boiling of the fluid. Truesdell 

and Janik (1986) and White (1986) presented further 

explanations of the isotopic variations in the 

geothermal reservoir.

The tritium content of samples collected from 

five Baca wells in 1982 and from three CSDP wells 

between 1985 and 1990 ranged between 0.18 and 1.1 

TU (Vuataz and Goff, 1986; .Goff and others, 1992). 

Using this range of tritium values and assuming a 

piston-flow model of the reservoir as one extreme and 

a homogeneously mixed model of the reservoir as the 

other, Vuataz and Goff (1986) calculated the residence 

time of water in the geothermal reservoir to be between 

60 and 10,000 years and on the basis of these and other 

geologic and geochemical data concluded that the 

mean residence time is at least several hundred years.

33
£ 1,000 

0

o

2 500

CC 

UJ 

Q. 

C/5

CC

O

-j 100

£ 50

10

Li Na K Ca S04 B Cl Br HCO3SIO2 

CONSTITUENT

Figure 13.-Range of concentrations of geothermal-reservoir fluids collected in 1982 from

five Baca wells (modified from Truesdell and Janik, 1986, fig. 4). Well locations 

shown in figure 5.

-40

-50

-60

g -80

-90

-100

-110

 RESERVOIR WATER (wells)

A DERIVATIVE WATER (wells and springs)

D THERMAL METEORIC WATER (springs)

O ACID-SULFATE WATER (Sulphur Springs area)

NOTE: Some points represent the average of 

two or more analyses

HYPOTHETICAL HIGH-LEVEL RESERVOIR

FLUID BENEATH SULPHUR SPRINGS

(GOFF AND OTHERS, 1985, FIG. 5)

FOOTBATH, 

- SULPHUR SPRINGS

o «- (5 180(C02 -H2 0)

FRACTIONATION

VALLES METEORIC

WATER 

(VUATAZANDGOFF, 1986)

METEORIC-WATER LINE 

FOR JEMEZ MOUNTAIN AREA

MUD POT,

SULPHUR SPRINGS 

O

FUMEROLE STEAM, 

SULPHUR SPRINGS

-22 -20 -18 -16 -14 -12 -10

OXYGEN-18, IN PER MIL

-8 -6 -4 -2 

MODIFIED FROM GOFF AND OTHERS, 1992, FIG.4, 

AND PUBLISHED WITH PERMISSION; DATAFROM 

VUATAZ AND GOFF, 1986, TABLE 1; AND GOFF AND 

OTHERS, 1992, TABLE 1

Figure 14.-Relation of deuterium and oxygen-18 for selected thermal and nonthermal fluids 

in the Jemez Mountains region.

34
Fluid Flow in the Reservoir

Several conceptual models of fluid flow in the 

geothermal reservoir have been developed by different 

investigators, and these models are in general 

agreement with one another. A generalized model 

based on these concepts is illustrated in figure 11. Faust 

and others (1984) and Goff and others (1985) proposed 

that the mountains within the caldera, those that form 

its rim, and the moat valleys of the caldera are recharge 

areas for the geothermal reservoir. Vuataz and Goff 

(1986) similarly proposed that the entire 14- to 18- 

mile-diameter caldera depression and surrounding 

highlands serve as the recharge area to the geothermal 

reservoir, and further, that the moat valleys of Valle San 

Antonio, Valle Toledo, and Valle Grande, in the north 

and east areas of the caldera (fig. 6), are probably the 

principal recharge zones of the reservoir because of 

their large areal extent, accumulations of sediment, and 

the streams draining most of the highland areas that 

flow into these valleys. Based on the deuterium content 

of water from five Baca wells, the average recharge 

altitude of the geothermal reservoir is between 8,300 

and 9,480 ft (Vuataz and Goff, 1986), which is in good 

agreement with altitudes in the caldera. Altitudes of 

caldera valleys range from 7,875 ft in the southwest to 

about 8,800 ft in the northeast and along the caldera rim 

exceed 10,000 ft; Redondo Peak reaches 11,254 ft.

The isotopic content of water from wells in the 

Redondo Creek subsystem indicates two different 

types of water, suggesting that different areas recharge 

different parts of the reservoir. Water from Baca wells 

4 and 13 is isotopically lighter (larger negative values) 

than water from Baca wells 15,19, and 24 (fig. 14). The 

deuterium content of water from Baca wells 4 and 13 is 

similar to that of water in Redondo Creek about -90 

and -85 per mil. The similarity in deuterium content of 

the reservoir and creek water, the proximity of wells 

and the creek, and the estimated recharge altitude of 

reservoir water suggest that the source of recharge for 

water from wells 4 and 13 is the Redondo Peak area 

(White, 1986). The heavier deuterium content of water 

from Baca wells 15, 19, and 24 may represent a lower 

source of recharge for this water, possibly the valley 

areas of the caldera, or the heavier deuterium content of 

the water could result from fractionation during boiling 

or from mixing with other water, such as that 

occupying the deeper Precambrian rocks. Further 

discussion of the origin of the two types of water in the 

Redondo Creek subsystem can be found in Smith and

Kennedy (1985), Truesdell and Janik (1986), and 

White (1986).

Specific flow paths of recharge water and water 

within the Valles Caldera geothermal reservoir have not 

been precisely defined. Cooler recharge water probably 

flows downward around the outer edges of the reservoir 

or along the caldera ring fractures, enters the reservoir 

at depth, is heated, and then rises convectively within 

the reservoir (Faust and others, 1984). Some ground 

water in the perched aquifers probably recharges the 

geothermal system by downward leakage through 

relatively impermeable welded tuff and the reservoir 

caprock. However, the amount of downward flow 

through the tuff and caprock is probably inadequate to 

be the primary source of recharge to the reservoir. 

Instead, downward flow along fault zones and fractures 

is probably the primary mechanism of recharge to the 

reservoir. As indicated above, much of the water 

recharging the geothermal reservoir probably does not 

come from areas directly above and immediately 

surrounding the reservoir, but reaches the reservoir by 

lateral flow.

Temperature gradients in the geothermal 

reservoir area provide insight into possible flow paths 

of recharge to the reservoir. The shallow temperature 

gradients (fig. 10) decrease sharply to the southeast 

between the faults that form the Redondo Creek 

Graben; deep ground-water temperature contours at 

about 3,280 ft above sea level exhibit a similar pattern 

in the reservoir (Wilt and Vonder Harr, 1986, fig. 4). 

These temperature patterns suggest the inflow of cooler 

recharge water from the southeast downward along the 

fault zone that borders the Redondo Creek Graben to 

the east (Bodvarsson and others, 1982).

Well temperature and pressure information also 

indicate that within the Redondo Creek reservoir, 

thermal water generally flows upward and then 

laterally toward the southwest. Reservoir temperatures 

generally increase toward the north within the Redondo 

Creek area and toward the northern part of the Sulphur 

Creek area (Baca wells 7 and 8). Measured 

temperatures in the liquid-dominated zone penetrated 

by wells VC-2A and VC-2B (about 200 °C) are lower 

than those in Redondo Creek area wells and Baca wells 

7 and 8 (250 to 300 °C). Grant and others (1984) 

suggested that heated fluids rise under the northern part 

of the Sulphur Springs area and flow laterally toward 

the Redondo Creek area. Swanberg (1983) suggested 

that available well-temperature information was 

consistent with two zones of convective upflow, one at

35
the head of Redondo Creek and bounded by faults of 

the Redondo Creek Graben and the other bounded by 

graben faults in the Sulphur Creek area. Grant and 

others (1984) also argued for a hydrologic connection 

between these two areas based on similar pressures in 

Baca wells 7 and 9 and those in Redondo Creek area 

wells. However, thermal and chemical data for the 

more recently drilled CSDP wells and well WC23-4 

located west of well VC-2A appear to favor a separate 

flow system within the more southerly parts of the 

Sulphur Creek area and the ring-fracture zone to the 

west.

Grant and others (1984) showed that pressure 

measurements in Baca wells 7 and 8 and Redondo 

Creek area wells define a consistent gradient within the 

reservoir that corresponds to a hydrostatic gradient at 

about 260 °C. This indicates that reservoir fluid moves 

through the Redondo Creek reservoir in permeability 

channels as natural flow within the reservoir. The 

pressure gradient also indicates upward flow in regions 

where temperatures exceed 260 °C and the nominal 

potentiometric surface of the reservoir (the altitude at 

which the pressure gradient extrapolates to 

atmospheric pressure) is about 7,900 ft above sea level 

or 1,100 ft below a land-surface altitude of 9,000 ft.

Thermal water discharges laterally from the 

geothermal reservoir toward the southwest where 

Canon de San Diego intersects the rim of the caldera. 

Such discharge from a geothermal reservoir is 

commonly referred to as a hydrothermal outflow 

plume. A plume from the Valles Caldera had been 

postulated by various investigators. Dondanville 

(1971) first proposed that the hot springs in Canon de 

San Diego represent outflow from the geothermal 

reservoir in the caldera. Before Dondanville's report 

was released in 1978, Trainer (1974) independently 

recognized that the chemistry of two groups of hot 

springs along the Jemez Fault Zone in Canon de San 

Diego was similar to that of deep geothermal fluids 

within the caldera and proposed that these springs were 

caused by subsurface discharge from the geothermal 

reservoir. Goffand others (1981) added further support 

to this idea, and included geologic, chemical, and 

isotopic evidence. CSDP core hole VC-1 (fig. 5), 

drilled in 1984, intersected the hydrothermal discharge 

plume in the Madera Limestone at a depth of about 

1,575 ft (Gotland others, 1988). The hole was drilled 

in the southwest moat near the intersection of the ringfracture zone and the Jemez Fault Zone (fig. 5), which 

is approximately midway between the geothermal

reservoir and the hot springs in Canon de San Diego. 

The discharge plume from the Valles Caldera was 

described in detail by GofTand others (1988). They 

considered stratigraphic, temperature-gradient, and 

hydrogeochemical data to define the configuration and 

chemical characteristics of reservoir discharge. The 

following description of the discharge plume draws 

primarily from their work.

Discharge of thermal water from the caldera 

comes from at least two subsystems, Redondo Creek 

and Sulphur Springs. On the basis of estimated 

discharge rates, thermal gradients, heat flow estimates, 

and geochemical mixing relations, Goffand others 

(1988) estimated that about 25-50 percent of the 

discharge plume is channeled along vertical conduits in 

the Jemez Fault Zone where it intersects the caldera. 

The fault zone, which conducts a large portion of the 

flow, constitutes no more than 10 percent of the area 

affected by the discharge. The remainder of the 

discharge is assumed to be distributed for about 6,500 

ft on either side of the fault zone and contained 

primarily in horizontal, semipermeable Paleozoic 

strata above the contact with Precambrian crystalline 

rocks. The lateral extent of discharge from the 

geothermal reservoir has not been fully defined.

GofTand others (1988) assumed, on the basis of 

proximity alone, that the Redondo Creek subsystem 

contributes most of the thermal water to the Jemez 

Fault Zone and that the Sulphur Springs subsystem 

contributes the thermal water flowing under the Jemez 

Plateau west of the caldera. The thermal water mixes 

with dilute nonthermal water as it moves laterally away 

from the reservoir. On the basis of this assumption and 

on geochemical data, Goffand others (1988) calculated 

that water of the discharge plume, where sampled by 

CSDP hole VC-1, is composed of approximately 30 

percent geothermal water from the Redondo Creek 

subsystem and that the discharge plume flowing under 

the Jemez Plateau could be composed of as little as 15- 

25 percent geothermal water from the Sulphur Creek 

subsystem. Grant and others (1984) suggested that 

thermal waters from the Sulphur Springs subsystem 

flow toward the Redondo Creek subsystem and then 

down Canon de San Diego. However, analysis of data 

for wells in the Jemez Plateau area west of the caldera, 

discussed in the next section, suggests otherwise.

The total rate of thermal-water discharge from 

the Valles geothermal system is difficult to determine 

because most shallow discharge of thermal water

36
occurs as diffuse seepage into streams. Thermal water 

from the Valles Caldera outflow plume can be 

identified in hot springs at Soda Dam and Jemez 

Springs (H-6 and VA-10, respectively, fig. 5) in Canon 

de San Diego and in various wells drilled adjacent to 

the southern and western edges of the caldera. The 

model of Faust and others (1984) simulated 

predevelopment conditions in the geothermal system 

with an input of approximately 2,030 acre-ft/yr of hightemperature water at the base of the geothermal 

reservoir. In their model, 1,300 acre-ft/yr of this inflow 

moves through the system and eventually discharges 

into the Jemez River. This value is between other 

estimates, which are based on chemical flux 

measurements, of input of Valles-type thermal water to 

the Jemez River of 715 acre-ft/yr upstream from San 

Ysidro (fig. 1) and 2,550 acre-ft/yr at its confluence 

with the Rio Grande. These estimates may include 

contributions of mineralized water from the stream 

draining the Nacimiento Mountains west of Canon de 

San Diego (fig. 1). This subject is discussed further in 

following sections.

SOUTHWESTERN JEMEZ MOUNTAINS

Hydrothermal features in the Jemez Mountains 

outside the Valles Caldera are restricted to the 

southwestern part of the region and largely to a specific 

part of it, Canon de San Diego. Fumaroles and thermal 

mineral springs in the canyon indicate subsurface 

drainage of geothermal fluid from the caldera. Until the 

onset of research activity in Valles Caldera beginning 

in the 1970's, the thermal springs in Canon de San 

Diego (at Jemez Springs and Soda Dam in fig. 1) were 

the best known geothermal features in the Jemez 

Mountains. They had been used by pueblo Indians who 

lived in the canyon before the Spanish came to New 

Mexico, were observed by expeditions sent through the 

Southwest by the U.S. Government, and were in part 

later developed for bathing. After settlement of the 

village of Jemez Springs at least two bathhouses were 

built and maintained, and the village became a popular 

resort. Water samples from Jemez Springs were 

chemically analyzed as early as 1875 (Summers, 1976, 

p. 38). Several drill holes outside the canyon have 

penetrated mineral water that contains a component of 

geothermal-reservoir fluid; no other evidence of such 

fluid has been found elsewhere in the Jemez 

Mountains.

The southwestern Jemez Mountains region (fig. 

1) extends west and south from Valles Caldera to the 

San Pedro Mountains and the Nacimiento Mountains, 

south to the village of San Ysidro, and southeast to the 

Rio Grande north of Bernalillo. It includes the western 

marginal fault zone of the Rio Grande Rift. North of 

Jemez Pueblo, the fault zone is entirely in consolidated 

rocks, which extend into the rift; south of the pueblo, 

the fault zone separates tuff and sedimentary and 

crystalline rocks outside the rift from thick basin-fill 

deposits and volcanic rock within it. The fault zone is 

complex and is composed of two or more major faults 

that extend southward across the region.

Between the caldera and the villages of 

Ponderosa and Canon (fig. 1), the topography consists 

of long, narrow mesas capped by Bandelier Tuff and of 

intervening canyons cut into the underlying 

sedimentary rocks. Farther south erosion has largely 

removed the tuff, and irregular topography has 

developed on valley-fill deposits and consolidated 

rocks. The major valleys are Canon de San Diego, 

which breaches the rim of the caldera and extends as a 

narrow canyon to the vicinity of Canon, then southward 

to San Ysidro as a wide valley, and the canyons of the 

Rio Cebolla and Rio Guadalupe, west and southwest of 

the caldera. The Rio Guadalupe joins the Jemez River 

near Canon. The Jemez River flows into the Rio Grande 

near Bernalillo.

The rocks exposed over most of the 

southwestern Jemez Mountains region are consolidated 

rocks of late Paleozoic age (table 1, Jemez Plateau 

column): limestone and subordinate sandstone of the 

Carboniferous Sandia Formation and Madera 

Limestone and sandstone, siltstone, and subordinate 

limestone in the Permian Abo, Yeso, and San Andres 

Formations. This section unconformably overlies 

Precambrian granitic and gneissic crystalline rocks, 

which outcrop only locally in this region but are 

exposed over considerable areas in the Nacimiento 

Mountains to the west. Deep wells outside the western 

rim of the caldera penetrate the crystalline rocks about 

2,100 to 2,400 ft beneath the .surface of the plateau. 

Near the southern edge of the region, at and east of 

Jemez Pueblo, the consolidated rocks are overlain by 

sandy, Tertiary rift-fill deposits (Zia Sand and Santa Fe 

Group) (table 1, Rio Grande Rift column), which are, 

at places, overlain by or intercalated with Tertiary 

volcanic rocks. The Pleistocene Bandelier Tuff rests 

unconformably on the old sedimentary rocks 

throughout the northern part of this region, extending

37
south to the Canon area. Post-Bandelier Tuff volcanic 

rocks of several eruptive episodes were emplaced in 

and near the ring-fracture zone; one flow extended into 

Canon de San Diego near the rim of the caldera.

Near the caldera, the surface of the crystalline 

rocks and overlying sedimentary strata dip gently south 

and southwest. In Canon de San Diego, upstream from 

Jemez Springs, the gradient of the valley floor is greater 

than the dip of the strata, so a northward (up canyon) 

traverse rises through the stratigraphic section. The 

canyon cuts into Carboniferous rocks from Jemez 

Springs to near the confluence of the East Fork Jemez 

River and Jemez River (fig. 5), into Permian rocks to 

the vicinity of Spence Spring (H-42, fig. 5), and beyond 

that into volcanic rocks. Southward from Jemez 

Springs, through a slight change in dip of the strata, the 

Permian rocks are at the surface as far south as Jemez 

Pueblo; the Carboniferous rocks are exposed only in 

eroded folds and fault blocks northwest and west of 

Canon and Jemez Pueblo. This areal distribution of 

Carboniferous limestones may control the distribution 

of mineral springs in and near Canon de San Diego. So 

far as is known, the Valles Caldera discharge plume is 

present only in and near the limestone.

Faults in the southwestern Jemez Mountains are 

concealed throughout much of their extent. They are 

undoubtedly more numerous, and their pattern more 

complex, than indicated by figures 2 and 5.

Numerous investigators have noted the 

significance of the marginal fault zone along the west 

side of the Rio Grande Rift in the Jemez Mountains to 

the flow of geothermal fluid out of Valles Caldera, in 

particular Goff and others (1988). Near Soda Dam, 

mapping of the Jemez Fault Zone and travertine 

deposits cut by it was updated by Goff and Kron 

(1980). Subsequent study of these travertine deposits 

using uranium-thorium dating and stable-isotope 

analyses (Goff and Shevenell, 1987) has documented 

the million-year history of the hydrothermal system in 

the Valles Caldera.

Not until the 1970's was a connection drawn 

between the thermal mineral waters in Canon de San 

Diego and the geothermal reservoir in Valles Caldera. 

Dondanville (1971) pointed to general geologic 

relations and chemical similarity between these springs 

and geothermal fluid and drew the first credible 

inference of a caldera source for the mineral-spring 

waters. Woltz (1972) concluded from study of selected 

chemical constituents that the water, as well as other 

water in the region, contains contributions from

magmatic sources. Earlier work by White and others 

(1963, p. 42) had shown the water at Jemez Springs to 

be typical of thermal water in non-geyser areas 

associated with volcanism, and Trainer (1974) used 

their characterization of major and minor constituents 

to argue a caldera source for the spring water. 

Additional critical information provided by other 

investigations reinforced the hypothesis of a caldera 

connection. Deep drilling by the LANL well GT-2 at 

the LANL hot-dry-rock site just outside the western 

rim of the caldera (fig. 5) found mineralized water in 

the basal limestone and in fractures in the upper part of 

the underlying gneiss (Pettitt, 1975a, p. 7; Trainer, 

1978, table 5, well N4). Based on the chemical 

composition and calculated temperature, the water 

from this well appeared to have come from the caldera. 

Hydrochemical data for deep wells in the caldera had 

not been released at that time, but Trainer (1975) 

assumed that the water from the LANL well 

represented a geothermal-fluid end member mixed 

with native, nonthermal ground water. Trainer used a 

simple mass-balance calculation to show that the 

mineral-spring water could be explained by such 

mixing.

Further support for the concept of the escape of 

geothermal fluid from the caldera came from three 

additional investigations. Two surface-geophysical 

studies, in the ring-fracture zone near the head of 

Canon de San Diego (Jiracek, 1974; Jiracek and others, 

1975) and in the canyon near Jemez Springs (Pearson 

and Goff, 1981), detected low resistivity and thus the 

suggestion of mineralized water. Finally, CSDP test 

hole VC-1 (fig. 5) penetrated several conduits 

containing thermal water, and cores revealed extensive 

alteration and mineralization of the country rock, 

which indicate that flow in the past occurred at 

temperatures higher than those of the present (Goff and 

others, 1988). The test hole also provided a wide range 

of additional information on rock structure and 

stratigraphy, heat flow, and chemistry and stable 

isotopes of water and rocks.

Further information came from test holes drilled 

by the Village of Jemez Springs and by the USGS. The 

village well was drilled in 1979 to explore the potential 

for development of hot water for space heating. Data 

from the well (Goff and others, 1981), together with 

results of the surface resistivity soundings in the 

canyon floor (Pearson and Goff, 1981), represent the 

only geothermal information, other than chemical and 

isotopic analyses, for a site this far south in Canon de

38
San Diego. A significant result of this work at Jemez 

Springs was an emphasis on the differences between 

the mineral water at Jemez Springs and Soda Dam; 

Goffand others (1981, p. 241) and Trainer (1984, p. 

255) concluded that flow and mixing must occur in 

more than one system of conduits in the Jemez Fault 

Zone. White and others (1984, p. 262) argued the same 

point on the basis of water chemistry.

Thermal and cold mineral water west and 

northwest of San Ysidro, near and along the west front 

of the Nacimiento Mountains, resembles the Valles 

Caldera hot mineral fluid in terms of major chemical 

constituents, except for large concentrations of sulfate; 

on this basis Trainer (1974, 1975) thought that the 

thermal and cold mineral water might be mixed water 

derived in part from the caldera. Subsequent study of 

additional chemical analyses and stable-isotope data 

has shown the water to be unrelated to the Valles 

geothermal system (Goffand others, 1981, p. 241; 

Vuataz and Goff, 1986, p. 1843; Shevenell and others, 

1987, p. 22-25). This new interpretation raised the 

question of how far Valles-derived geothermal fluid 

travels through the Canon de San Diego.

Descriptive Hydrochemistry

Ground-water information for the southwestern 

Jemez Mountains region is limited; the region is rugged 

and semiarid, sparsely settled, and has few wells and 

developed springs. To some degree these obstacles to 

interpretation are offset by the distinctive geochemical 

character of the ground water, which aids in 

identification of the sources and evolution. Because 

chemical data provide a chief means of hydrologic 

investigation, the interpretive discussion begins with a 

brief description of the chemical characteristics of 

ground water in the region. Subsequent sections of the 

report consider (1) the mixing of mineralized water, 

with its implications for human use of ground water 

and (2) the nature of the ground-water system in the 

southwestern Jemez Mountains.

The major-ion composition of five samples 

thought to represent geothermal reservoir fluid in the 

Valles Caldera is shown in figure 15 A. The fluid is a Na 

Cl water whose chloride content (fig. 15B) is about 50 

to 100 milliequivalents per liter (meq/L) or 1,800 to 

4,000 mg/L. Minor constituents in samples from Baca 

wells 4,13, and 24 include As (1.3 to 2.3 mg/L), B (16 

to 29.6 mg/L), Br(3.6 to 13.6 mg/L), and Li (15 to 32.8 

mg/L).

The major ions in ground water in granitic and 

volcanic rocks in this area and in alluvium and 

colluvium derived from the volcanic rocks are 

summarized in figure 16. The grouping of data in figure 

16A represents a range of compositions from Na Ca 

HCC>3 water derived from the dissolution of Na- and 

Ca-rich minerals, such as feldspars, by water from 

precipitation containing atmospheric and biogenic 

carbonic acid. Concentrations of major and minor 

constituents in the ground-water samples are small and 

their respective flowpaths are believed to have 

penetrated to only shallow depths before returning to 

the surface.

Ground water in the Madera Limestone (fig. 17) 

generally has a Ca Mg HCO3 composition typical of 

water in carbonate rocks. Composition of water 

samples from the Abo Formation (fig. 18) suggests a 

wide range in lithologies, from calcareous to siliceous 

sandstone and shale. If a larger number of samples 

were available, the sample field probably would cover 

the entire southwestern part of the field, as in the 

volcanic and related detrital rocks (fig. 16, noted 

above) and rift-fill sediments (fig. 19).

The principal patterns in figures 15-19 are (1) the 

conspicuous differences in composition and 

concentrations of dissolved constituents in geothermal 

fluid and all other ground water and (2) the lesser but 

consistent differences between water in carbonate and 

in igneous rocks. These patterns are useful in 

interpretation of mixed water.

Mixtures of Water

Subsurface escape of reservoir fluid from the 

geothermal system beneath Valles Caldera, 

southwestward beneath and near Caflon de San Diego, 

has formed a discharge plume that extends 

downcanyon at least as far as Soda Dam and Jemez 

Springs. Study of travertine deposits at Soda Dam 

(Goffand Shevenell, 1987) has shown that subsurface 

discharge was active during much or all of the millionyear history of the caldera. Analytical data for well 

VC-1 (fig. 5) (Goff and others, 1988) show that near the 

caldera rim the plume consists of a mixture of reservoir 

and nonreservoir fluids. Mass-balance characterization 

of geothermal fluid mixing with native ground water 

along its flow path (Trainer, 1975, 1984) indicates 

mixing in and near Canon de San Diego.

39
(A)

VC-2B

Baca well 24 

VC-2A

Baca wells 4,13

CHEMICAL CONSTITUENTS

SO4 Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

CO, + HCO, Carbonate + bicarbonate

PERCENTAGE OF TOTAL IONS, IN MILLIEQUIVALENTS PER LITER

200

(B) oc 100

UJ

50

20

UJ

O 

a 2

Z '

O

I-

< 0.2

CC

O

Z

O 

O

0.05

0.02

0.01

Concentrations 

inwellVC-2A 

inthe Sulphur 

Springs area

Solid lines bound range 

of concentrations for 

3 samples from Baca 

wells4,13, and 24, 

Redondo Creek area

Ca Mg Na + K + LJ Cl + Br + F S04 CO3 + HCOg

CONSTITUENT

Figure 15.--(A) Major-ion composition and (B) concentrations in water from geothermal wells 

inthe Sulphur Springs and Redondo Creek areas (data from Goff and others, 

1992, table 1; and White, 1986, table 1). Well locations shown in figure 5.

40
(A)

EXPLANATION

 WATER FROM GRANITIC ROCKS

x NONTHERMAL WATER FROM VOLCANIC 

ROCKS

* WARM WATER FROM VOLCANIC ROCKS

A WATER FROM VOLCANIC ALLUVIUM AND 

COLLUVIUM

CHEMICAL CONSTITUENTS

SO. Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

C03 + HC03 Carbonate + bicarbonate

(B)

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

a: 10 

m

DC 

HI 

Q.

CO 

I- 2

Z 

HI

1 '

O 0.5 

HI

z 

o

0.1

0.05

HI

Z 0.02

O

o

0.01

Lines bound range 

of concentrations 

for 28 samples 

shown In (A)

Ca Mg Na + K + LI CI + Br + F S04 COa + HC03

CONSTITUENT

Figure 1 6. --(A) Major-ion composition and (B) concentrations in water from wells and springs in granitic 

rocks, volcanic rocks (chiefly rhyolitic and andesitic), and alluvium and colluvium derived 

from volcanic rocks (data from Purtymun and others, 1974, tables IX and X; Trainer, 1978, 

table 5; and Shevenell and others, 1987, table B-ll).

41
(A)

EXPLANATION 

 WELL 

«v SPRING

CHEMICAL CONSTITUENTS

SO4 Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

CO, + HCOo Carbonate + bicarbonate

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

(B)

cc

HI 

CL

COHZ 

UJ

D 

O 

UJ

z 

O

20

10

0.5

0.2 

< 0.1

Z 0.05 

O

o °-02 

o

0.01

Lines bound range

of concentrations for

7 samples shown in (A)

Ca Mg Na+K+Li CI + Br+F SO4 COg + HCOg

CONSTITUENT

Figure 17.--(A) Major-ion composition and (B) concentrations in water from wells and springs in 

the Madera Limestone (data from Purtymun and others, 1974, tables IX and X; 

Trainer, 1978, table 5; and Shevenell and others, 1987, table B-ll).

42
(A)

EXPLANATION 

 WELL 

«. SPRING

CHEMICAL CONSTITUENTS

SO4 Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

COo + HCOo Carbonate + bicarbonate

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

(B)

CO

LLI

8lit

3

100

2°

0.5

o °-2

< 0.1

Z 0.05

LLI

O

§0.02 

O 

0.01

Lines bound range

of concentrations fo

11 samples

shown In (A)

Ca Mg Na+K+Li CI+Br+F SO4 CO3+ HC03

CONSTITUENT

Figure 18.--(A) Major-ion composition and (B) concentrations in water from wells and springs 

in the Abo Formation (data from Purtymun and others, 1974, tables IX and X; 

Trainer, 1978, table 5; and Shevenell and others, 1987, table B-ll).

43
EXPLANATION 

«,, SPRING 

 WELL

CHEMICAL CONSTITUENTS

SO4 Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

CO3 + HCO3 Carbonate + bicarbonate

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

(B) 10

cc

UJ c i_ o

D

o

UJ

0.5

0.2

0.1

ft 0.05

z

UJ

o

O °-02 

O

0.01

Lines bound range

of concentrations for

13 samples

shown In (A)

Ca Mg Na+K+LI CI+Br+F SO4 CO3 +HCO3

CONSTITUENT

Figure 19.-(A) Major-ion composition and (B) concentrations in water from wells and springs in 

rift-fill deposits (Santa Fe Group and Zia Sand) (data from John and others, 1967; 

Trainer, 1978, table 5; and Goff and Sayer, 1980).

44
Two modes of transport move geothermal water 

and its solutes beneath Canon de San Diego. Flow is 

primarily in the subsurface, along fracture conduits 

controlled by rock structure and stratigraphy. Such flow 

brings mineral water to Soda Dam and Jemez Springs. 

Although the results of subsurface flow are apparent, 

the factors controlling its magnitude and areal extent 

are poorly known because of limited data. Subsurface 

flow is discussed in subsequent sections of this report.

The second mode is surface transport in the 

Jemez River downstream from Soda Dam and Jemez 

Springs, along with associated ground-water underflow 

in alluvium beneath and beside the stream and in 

fractured bedrock near the stream that is hydraulically 

connected with overlying alluvial deposits. Areal 

changes in major-ion composition of water in the 

Jemez River system is shown in figure 20. The figure is 

based on samples collected over a period of years from 

June to September when the streamflow is largely or 

entirely base runoff (ground water discharged to the 

stream).

Samples from the East Fork Jemez River in Valle 

Grande (site 1 in fig. 20) and from San Antonio Creek 

(site 2) in Valle Toledo contained less than 3 mg/L Cl 

(Cl brought to the region in precipitation) and about

100 mg/L dissolved solids. The Ca Na HCO3 

composition is typical of ground water in volcanic 

rocks and their detritus. These two streams form the 

surface drainage of Valles Caldera. Before leaving the 

caldera, San Antonio Creek receives the flow of creeks 

draining the Sulphur Springs area, but those streams 

are so small that they have little effect on water quality 

in the much larger San Antonio Creek except for the 

contribution of 864 and low pH from one stream. Just 

downstream from the confluence of San Antonio Creek 

and the East Fork Jemez River (site 3), the water 

composition differs only slightly from that in the 

caldera. To this point the streamflow consists largely of 

the combined discharge of numerous cold springs and 

several warm springs that drain volcanic rocks. The 

dissolved-solids concentration in summer months is 

about 50 mg/L and Cl averages less than 5 mg/L. 

Summer base runoff is about 10 to 12 ft3/s. Between 

the confluence and a point just upstream from Soda 

Dam (site 4) the composition of stream water 

approaches that of water in limestone (near the left 

vertex of the diamond field in fig. 20) as a result of 

inflow from small limestone springs, several of which 

are represented in figure 17.

Locations of sampling sites

SAN ANTONIO CREEK 

IN VALUE TOLEDO

GAGING STATION, 

JEMEZ RIVER 

BELOW EAST FORK, 

NEAR JEMEZ SPRINGS

JEMEZ RIVER 

BELOW SODA DAM

RIOGUADALUPE 

ABOVE JEMEZ RIVER

GAGING STATION, 

JEMEZ RIVER 

NEARJEMEZ

CHEMICAL CONSTITUENTS

EAST FORK

JEMEZ RIVER .

INVALLEGRANDE /.

RIOSALADO ABOV 

JEMEZ RIVER

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

Sulfate

Chloride

Calcium

Magnesium GAGING STATION, 

Sodium + potassium JEMEZ RIVER--

Carbonate + bicarbonate BELOW JEMEZ

CANYON DAM

Figure 20.-Downstream change in major-ion composition of water in the Jemez River system 

and map showing location of sampling sites (data from Trainer, 1978, tables 6 

and 11; and files of the U.S. Geological Survey).

45
At Soda Dam, about 400 gal/min of mineralized 

water containing more than 4,000 mg/L dissolved 

solids (Trainer, 1984, based on 1973-74 data) issues 

from springs. About a quarter of a mile downstream 

from Soda Dam (site 5), the dissolved-solids 

concentration of the stream water doubles and its 

composition approaches the composition of the 

geothermal fluid (center of the diamond plot, fig. 20). 

An additional inflow of mineralized water (an 

estimated 365 gal/min containing about 2,500 mg/L 

dissolved solids) occurs at Jemez Springs. These 

mineral-spring waters have large concentrations of Cl 

and HCO3 , which tend to offset each other's effects on 

the diamond plot.

The Jemez River has an Na Ca HCC>3 

composition and carries about 550 mg/L dissolved 

solids and 150 mg/L Cl (fig. 20, site 6). The Rio 

Guadalupe, which drains volcanic and limestone 

terranes, has a composition dominated by Ca and 

HCO3 and carries about 250 mg/L dissolved solids and 

less than 10 mg/L Cl (fig. 20, site 7). The composition 

of the combined flows of the streams, as measured at 

the USGS streamflow-gaging station Jemez River near 

Jemez (fig. 20, site 8), about 1 mi downstream from the 

confluence, becomes similar to water in limestone. 

With increasing distance downstream from the gaging 

station, however, at Jemez Pueblo (fig. 20, site 9) and 

downstream from the pueblo (fig. 20, site 10), Na and 

Cl again increase. This change is attributed to the 

discharge of mineral springs; one well-documented 

spring discharges directly into the river through its bed 

and another is known near the river.

Near San Ysidro the Jemez River is joined by the 

Rio Salado (fig. 20, site 11), which drains the western 

front of the Nacimiento Mountains near their southern 

end. The mountains are fault controlled, and numerous 

mineral springs, active and extinct, occur along the 

fault zone. Water in the Rio Salado, derived from the 

Madera Limestone and overlying Mesozoic rocks that 

are in part gypsiferous, is more highly mineralized (in 

one September sample, dissolved solids was 11,040 

mg/L and Cl was 2,370 mg/L) than the Valles 

geothermal fluid. The Rio Salado channel south of San 

Ysidro is dry during much of the summer but the flood 

plain is coated with free salts that are transported with 

runoff during the next thunderstorm. As a result, and 

despite the much larger flow of Jemez River, the 

composition of the combined stream near the 

southeastern edge of the study area (fig. 20, site 12) 

shifts significantly toward the right apex of the 

diamond plot (fig. 20).

The composition of ground water in alluvial 

deposits (fig. 21) shows a pattern of change similar to 

that in the Jemez River. Water from volcanic rocks and 

their detritus (fig. 21, site 1) probably contains a small 

component derived from the limestone exposed in the 

nearby canyon. In water from site 2 the limestone 

influence is more pronounced. Samples from sites 3-6 

exhibit the influence of the mineral springs at Soda 

Dam and Jemez Springs (a pronounced shift to the right 

in the diamond plot). The scatter at Jemez Pueblo 

(fig. 21, site 7), indicating local variability in 

composition, is attributed to a combination of recharge 

from losing reaches of the stream and mineral-spring 

discharge into the alluvial aquifer from the underlying 

bedrock. Additional mineral-water inflow causes 

changes at sites 8 and 9; the Rio Salado influence (an 

increase in Ca, 864, and Cl) is reflected in samples 

from sites 10 and 11.

Mineral Water near the Caldera as 

Derivatives of Geothermal Fluids

The mineral waters at Jemez Springs and Soda 

Dam are the most obvious in the southwestern Jemez 

Mountains. However, mineral water has been 

penetrated in four wells in the area: well GT-2 (at 

Fenton Hill); wells PC-1 and PC-2 (near Fenton Hill); 

and well VC-1 in the ring-fracture zone (fig. 5).

Well GT-2 is one of several deep holes drilled by 

the LANL on the plateau outside the western rim of the 

caldera; at the time of its completion at a depth of 6,356 

ft, the well was the deepest in the Jemez Mountains 

outside the caldera. Water was recorded in the lower 

part of a section of volcanic and sedimentary rocks that 

totals about 2,400 ft. The underlying crystalline rock is 

of very low permeability except in fractured zones near 

its upper surface. Water flowing through the deeper 

levels of the sedimentary rock is inferred, from 

temperature and chemistry data, to have come from the 

caldera. Some aspects of water chemistry are obscured 

by contamination from drilling and grouting fluids.

Five water samples were collected in 1974 

during the drilling of well GT-2. Despite contamination 

from drilling and grouting fluids, the water is similar in 

chemical composition to mineral water from the Canon 

de San Diego area; hence it was used as a hypothetical 

parent water in development of the hypothesis of 

mixing of reservoir and nonreservoir water (Trainer, 

1975). Subsequent release of analyses of reservoir 

fluids necessitates re-examination of well GT-2 data.

46
Locations of sampling sites

CHEMICAL CONSTITUENTS

SO4 Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

CO, + HC03 Carbonate + bicarbonate

10 KILOMETERS

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

Figure 21 .--Major-ion composition in ground water in alluvium along the Jemez River 

and map showing location of sampling sites (data from Trainer, 1978, 

tables 6 and 11; and Craigg, 1984, table 3).

Several physical and chemical signatures in 

ground water are indicative of high-temperature 

environments. Three signatures in the GT-2 samples 

suggest a caldera source for the water: a large 

concentration of dissolved SiC>2, indicative of high 

temperature; large concentrations of several trace 

constituents typical of hot water in volcanic regions; 

and a stable-isotope composition similar to those of 

several reservoir fluids in the caldera. Several trace 

constituents, expressed as ratios among themselves or 

with Na or Cl, have been widely used in geothermal 

studies, including several in this region. Two trace 

ions B and Li are used here in re-examination of the 

1974 data. The plots in figure 22 illustrate geochemical 

similarities among the geothermal-reservoir fluids and 

the mineral water outside the caldera. Prolonged 

circulation of hot reservoir fluid has led to 

accumulation of Li, B, Br, and As concentrations far 

larger than those present outside the caldera where 

nonthermal water circulates through similar rocks. The

ratios of these trace constituents are preserved even 

when the geothermal fluid becomes diluted. Li, B, and 

Br are conservative tracers; thus, the data points shown 

in figure 22 approximate straight lines despite the wide 

ranges in concentration. The major constituent Cl is 

commonly used in conjunction with trace ions because 

only small concentrations of Cl are present in ground 

water outside the caldera.

Concentrations of trace constituents in well 

GT-2 water are unlikely to have been affected by 

contamination from drilling and grouting fluids; hence, 

relations such as those shown in figure 22 were used to 

estimate an original major-constituent analysis of the 

water. Data from each of several wells in the caldera 

were used; the concentration of each major constituent 

(except F, for which the analyzed value was accepted) 

was plotted against a trace constituent (such as Ca and 

B, Mg and B, and Cl and B) to form a series of curves 

similar to those in figure 22. The original 

concentrations of Ca, Mg, and Cl were estimated by

47
40

35

CC

LU 30

H

_l

DC

LU

0- 25

CO

2 

<

DC

CD 20

£ 15

O 

EC

§ 1°

:

VC-1 (2)

/"/ 

I /

' 1 /

1 / s' r'"

y.

s ~/^ t / \ 

I / 1

/^ '

/

N \ 

1

Jemez Sp 

9 values

VC-2A

7/

4

Soda Dam 

14 values

ings-

/

/

GT-2

 /

WC23-4 (dep

" VC-2B

h 364 feet) '.

'-

'-

'-

'-

'-

:

;

2,000 4,000 

CHLORIDE, IN MILLIGRAMS PER LITER

6,000

40

35

DC lil 30

CC

o! 25 

C/5

DC

O 20

? 15

10

:

:

 VC-1 (2) i'7

//>

13t 

/

/-/

t / \ 

1 / ' 

Y S

/ *\

\ 

/

'jemezSp 

9 values

VC-2A (5) 

GT-2,

y

4

Soda Oam 

14 values

ings-

/

f

/

A 

WC23-4 (def

V

^VC-2B

>th 364 feet) "

:

:

-

2,000 4,000 6,000 

CHLORIDE, IN MILLIGRAMS PER LITER

Figure 22.--Concentrations of selected pairs of ions in geothermal-reservoir-fluid samples and in 

mixed water (data from White, 1986, table 1; Shevenell and others, 1987, table B-ll; 

and Goff and others, 1988, table 2, and 1992, table 1). Numbers in parentheses are 

number of samples from one well averaged to give plot shown. Well and spring 

locations shown in figure 5.

using each curve and the B concentration for GT-2. The 

entire procedure was done twice, using B and Li, and 

the results were averaged to provide the estimated 

concentrations listed in table 6. Twenty-five mg/L B 

(well GT-2) is equivalent to about 2,900 mg/L Cl 

(caldera wells), and 25 mg/L Li is equivalent to about 

3,010 mg/L Cl, for an average estimated concentration 

of 2,955 mg/L Cl. The sums of cations and anions in 

this estimated analysis are 95.17 and 89.24 meq/L, 

respectively a precision comparable to that of many 

published analyses for geothermal water in this region. 

The estimated original concentration for well GT-2 in 

comparison to analyses of geothermal-reservoir-fluid 

samples is shown in figure 23.

The estimated original concentrations are an 

approximation of the original chemistry of the fluid 

that moved out of the geothermal reservoir and into 

flow conduits beneath the Jemez Plateau. The effect of 

any dilution that occurred along the path to well GT-2 

is thought to be shown, but the effects of dissolution of 

wall rock along the flow channels, which cannot be 

estimated reliably because of contamination from

drilling and grouting fluids, are not shown. From the 

data available, the precise nature of the escaping 

reservoir fluid is not known. (The reader is referred to 

Vuataz and Goff (1986, p. 1847) and Goff and others 

(1988, p. 6047) for a detailed discussion of the 

difficulties involved in interpretation of sourcereservoir and dilute-mixing fluids.) In general, the 

escaping geothermal-reservoir fluid is similar to 

composition and concentrations shown in figure 15. 

The fluid in well GT-2 is discussed in a later section. 

Wells PC-1 and PC-2 penetrated a volcanic and 

sedimentary section similar to that penetrated by well 

GT-2, and both passed through numerous perched 

saturated zones that contain dilute water. Both wells 

penetrated water-yielding zones in the lower Abo 

Formation and upper Madera Limestone that yield 

slightly mineralized water possible dilute mixtures of 

native ground wat^r and fluid from a geothermal 

reservoir. Well PC-1, which extends through the 

sedimentary rocks and into the underlying gneiss, 

penetrated several water-yielding zones in the lower 

part of the limestone that yielded mineralized water.

48
Table 6. Chemical data used for estimating original major-ion concentrations of water fro

[All concentrations in milligrams per liter. Data from Baca wells represent total concentrations in reservoir waters 

wellhead; other caldera well samples assumed to represent total concentrations. Sources of data: Baca wells, White 

VC-2B, and WC 23-4, Goff and others (1988, table 2; 1992, table 1); well GT-2, Trainer (1978

Source of sample 

(see fig. 5 for location)

Baca 4, June 11, 1982

Baca 13, June 4, 1982

Baca 24, June 18, 1982

VC-2A, August 27, 1987 

(average of 5 analyses)

VC-2B, January 17, 1990

WC23-4, January 4, 1983 

(depth 4,800 feet)

GT-2, April 23, 1974 

(analysis of sample)

Estimated original 

concentration of water

from well GT-2

Ca

3.52

3.35

14

5.9

78.5

80.5

1.7

.80

Mg

0.065

.035

.001

.14

.76

2.89

2.1

.01

Na

1,123.0

1,146

1,514

1,842

2,350

2,800

6,300

1,860

K

241.0

244

227

308

700

470

350

385

HCO3

155.0

168

72

273

105

360

6,820

248

S04

35.0

42

40

55

7.8

33

2,100

54

Cl

1,991

1,897

2,499

2,943

4,150

4,350

3,500

2,955
 Solid lines bound 

range of concentrations 

in reservoirfluids

HC03 

CONSTITUENT

Figure 23.--Major-ion concentrations in geothermal-reservoir-fluid samples and estimated original 

concentrations in water from well GT-2 (data from table 6). Calcium and magnesium 

minimum values truncated on graph because they are much smaller than 0.01 

mil I (equivalent per liter. Well location shown in figure 5.

The chemical analyses of water from well PC-1 

are presented in table 7. The last analysis listed was 

reconstructed and was prepared using the same 

procedure used for well GT-2. The reconstructed 

analysis shows only the effect of dilution on the parent 

geothermal fluid. Comparison of the actual and 

reconstructed analyses (fig. 24) shows the combined 

effects of contamination during drilling (probably 

Na2SO4 and CaSO4) and of dissolution of wall rock, 

reflected by a large increase in Ca, Mg, SO4, and 

HCO3 .Well VC-1, in the ring-fracture zone east of 

Canon de San Diego and near the Jemez Fault Zone, 

penetrated the outflow plume from the caldera. The 

2,750-ft section of volcanic and sedimentary rocks 

above the Precambrian crystalline rock contains 

several thermal-water-yielding horizons in limestone 

and sandstone (Goffand others, 1988, fig. 4). The 

reconstructed analysis represents the character of the 

water if it had been modified from parent reservoir fluid 

only by dilution. Comparison of the reconstructed 

analysis of water from well VC-1 (fig. 25) and the 

actual analysis indicates that the mixed water gained 

appreciable amounts of Ca, Mg, and HCO3 through 

dissolution of wall rock, contribution from local 

ground water, or both. Well VC-1 was drilled using 

methods that introduced no significant contamination.

Mineral Water in Canon de San Diego

Because sufficient information is available for 

Canon de San Diego to show the complexity of the 

mineral-water chemistry, this section discusses the 

canyon as a whole. The conceptual model of canyon 

geohydrology on which the discussion is based is 

illustrated in figure 26. Diagrammatic geologic section 

A-A' parallels the general southward trend of Canon de 

San Diego and the Jemez Fault Zone. No faults are 

shown in the canyon except at Soda Dam, where an 

east-trending fault extends out of the canyon and 

through the adjacent mesa. The occurrence of mineral 

springs at Soda Dam and Jemez Springs is fault 

controlled, but the locations of these springs are also 

controlled by the relations among the stratigraphic 

section, canyon floor, rock structure, and 

potentiometric surface of the regional aquifer. Soda 

Dam is situated at the lowest point at which its section 

of the Jemez Fault reaches land surface and at the place 

where basal beds of the Pennsylvanian limestone and 

sandstone section are folded upward along the fault. 

Jemez Springs is near the farthest point downcanyon at 

which limestone crops out at the surface.

50
Table 7. Chemical analyses of water from well PC-1

[Location of well shown in figure 5. PC-1-9, native ground water in perched aquifer in Abo Formation; PC-1-10,

Abo Formation; PC-1-11, Madera Limestone, mixed water with small dissolved-solids concentration; PC-1-1,

Madera Limestone, mixed water with large dissolved-solids concentration; PC-1-1C, reconstructed analysis.

Analyses from Shevenell and others, 1987, table B-II. --, no data]

Sample

PC-1-9

PC-1-10

PC-1-11

PC-1-1

PC-1-1C

Concentration, in milligrams per liter

Ca Mg Na K Li HCO3 SO4 Cl F Br B

6.0 3.8 366 6.0 -- 852 245 5.0 2.15 - 0.74

10.3 4.2 433 6.6 0.20 686 151 108 2.43 0.18 .74

78 73 740 55 1.64 2,636 245 50 6.78 .29 4.24

762 52.8 1,390 153 10.8 1,133 2,157 1,602 1.06 4.3 13.4

1.1 .001 850 132 124 28 1,500

100

DC 

LU

c '°

LU 

CL

CO1-

Z 

LU

1 '

O

LU

2 0.1

z

z" 

o

h-

{£ 0.01

z

LU 

O

Z

o 

o

n nm

: Actual : 

: analysis /"~'~"~~--^^ :

.(depth 1,/1i!teet)/ -. X.

i V; \ ;

l \ /

\ I ^/'

\ J :

: ^ /

. / Reconstructed : 

'. » analysis '.

\ 1

: \ ' :

\ '

. , /

Ca Mg Na + K+LJ CI + F + Br 

CONSTITUENT

SO. CO. + HCOQ

Figure 24.--Actual analysis and reconstructed analysis of major ions in water from well PC-1. 

Reconstructed analysis represents character of the water if it had not been 

contaminated but had been modified from parent reservoir fluid by simple dilution. 

Reconstructed calcium and magnesium minimum values truncated on graph because 

they are much smaller than 0.001 milliequivalent per liter. Well location shown in 

figures.

51
DC 

LLI 

Q_

COIz

LU

o

LU

Z 

O

100

50

20

10

5

2

1 

0.5

0.2 

0.1

LU 0.05 

O

z

O 0.02 

0.01

Actual

analysis

(depth 1,585 feet)

Ca

Reconstructed 

analysis

Mg Na + K + Li Cl + F + Br SO CO + HCOg

CONSTITUENT

Figure 25.--Actual analysis and reconstructed analysis of major ions in water from well VC-1 (analysis 

from Goff and others, 1988, table 2). Reconstructed calcium and magnesium minimum 

values truncated because they are much smaller than 0.01 milliequivalent per liter. Well 

location shown in figure 5.

Location of geohydrologic features

NORTH

x x x x x » x 

xxxxxxxx

X X X X X X v

EXPLANATION

I pool COLLUVIUM, ALLUVIUM 

IfflaOd (NOT SHOWN ALONG

JEMEZ RIVER), AND

VALLEY FILL

| V | VOLCANIC ROCKS

[ . j SANDSTONEAND SHALE

[J 1-| LIMESTONE

I ><! CRYSTALLINE ROCKS

LOCALITY:

1. Near Battleship Rock

2. Soda Dam

3. Jemez Springs

4. Spring near Carton

5. Spring at Jemez Pueblo

PERCHED AQUIFER

FAULT-Arrows show 

direction of 

relative movement

*^ GRAVITY SPRING

A ARTESIAN SPRING

A FUMAROLE

Figure 26.--Diagrammatic section showing generalized geohydrologic setting in Canon de San Diego.

52
From the ring-fracture zone, the canyon floor 

descends southward through much of the rock section. 

Limestone is exposed in the canyon floor from 

Battleship Rock (no. 1, fig. 26) to south of Jemez 

Springs (no. 3, fig. 26); farther south the canyon floor 

cuts into the overlying sandstone and shale and cuts 

into alluvium and valley fill near Jemez Pueblo. 

Geothermal fluid leaves Valles Caldera by way of 

cavernous zones in the limestone; minimal evidence 

suggests that flow in the limestone continues beyond 

Jemez Springs, possibly as far as Jemez Pueblo. The 

potentiometric surface is below the canyon floor at 

Battleship Rock, where a 200-ft test hole penetrated 

unsaturated rock containing thin zones of perched 

water. Between this site and Soda Dam, at some place 

not yet identified, the potentiometric surface rises 

above the level of the canyon floor; the springs at Soda 

Dam and Jemez Springs are artesian. So far as is 

known, the thermal water is confined south of Jemez 

Springs, where nearly everywhere sandstone and shale 

overlie the limestone. Evidence of this confinement is 

available at only a few places near Canon and Jemez 

Pueblo, however, and chemical comparisons between 

the mineral water from Valles Caldera and mineral 

water at the southern end of the Nacimiento Mountains, 

near Jemez Pueblo, are not known in detail.

Earlier studies noted remarkable differences in 

temperature, chemical composition, and constituent 

concentrations between the mineral water at Soda Dam 

and at Jemez Springs, indicating flow along different 

paths. A principal difference is in 864 content, which 

is larger at Jemez Springs than in any other spring or 

well. Smaller but still anomalous 864 concentrations in 

ground water occur along much of the length of the 

canyon; they are thought to reflect the oxidation of H2S 

that has escaped upward from the thermal-water 

conduits. This mechanism does not, however, 

adequately explain the large SO4 content of the water 

at Jemez Springs.

Area near Rim of Caldera

The geohydrologic setting in Canon de San 

Diego just outside the rim of the caldera is complex. 

First, this locality is in the principal area of fumaroles 

outside the caldera (Bailey, 1961), which indicate the 

presence of boiling fluid at depth. A second notable 

characteristic is the diverse occurrence of shallow 

ground water. Three springs (H-31, H-32, H-35) on the 

hillside drain three different perched water-yielding 

zones in the limestone, and two test holes (H-29, H-30) 

penetrate two additional perched zones in limestone. A 

water-supply well (H-33) taps unconfined water, about

15 ft beneath river level, thought to represent a groundwater mound beneath the stream. Chemical data (table 

8) for water samples from those six sources show the 

water to be distinctly different from one another. Well 

H-3 3 yields native ground water, but the other two 

wells and three springs yield water that contains 

components of geothermally derived materials (Cl, 

trace constituents) and ranges widely in composition 

and concentration.

Samples from well H-29 and spring H-32 (fig. 

27A) indicate most clearly the mixture of geothermal 

and nongeothermal constituents (see, for comparison, 

site 5 in fig. 20). The sample from well H-30 is typical 

of water in limestone, although its position in figure 

27A suggests a mixture with a small proportion of 

geothermal water (hence its appreciable contents of Li 

and B, table 8) and with water of near-surface volcanicalluvial origin (well H-33). Therefore, well H-30 likely 

intersects the outer edge of the ground-water mound 

beneath the river, which may extend westward into the 

limestone.

The sample from spring H-31 is in an anomalous 

position in the diamond plot in figure 27A, but its 

composition can be seen more clearly in the 

semilogarithmic plot in figure 27B. The sample has 

small concentrations of Ca and Cl and a large 

concentration of Na. This characteristic is attributed to 

cation exchange by which the water lost Ca and gained 

Na.

Periodic observations revealed two types of 

water-level fluctuations in this area near the caldera 

rim. Spring H-32 drains a water-yielding zone in the 

limestone that is in hydraulic connection with the river 

at some point upstream, and fluctuations in discharge 

and chemical composition of the spring water reflect 

changes in the amount of recharge from the stream. 

Well H-29 intersects a water-yielding zone in the 

limestone that seems to be hydraulically isolated from 

the river; thus, its fluctuations are independent of 

stream stage.

Spring H-32 was observed periodically for 

nearly 2 years (fig. 28). Concentrations of the indicator 

constituents Cl and HCO3 conversely reflect the 

fluctuations in stream discharge. Fluctuations were 

conspicuous in 1973, a year of large spring floods in the 

river, and inconspicuous during 1974. The plots for Cl 

and HCC>3 (1973) show that stream water, which began 

to enter the aquifer during the rising river stage in early 

March, mixed with the resident ground water 

proportional to the increase in spring discharge.

53
Table 8. Chemical analyses of six ground-water samples, Canon de San Diego

near the rim of Valles Caldera

[Concentrations in milligrams per liter; , no data; °C, degrees Celsius. Locations shown in figure 31. 

Analyses from Trainer, 1978, table 5, except for well H-33 from Purtymun and others, 1974, table X]

Constituent or 

property

Silica (SiO2)

Calcium (Ca)

Magnesium (Mg)

Sodium (Na)

Potassium (K)

Carbonate (CO3)

Bicarbonate 

(HC03)

Sulfate (SO4)

Chloride (CD

Fluoride (F)

Arsenic (As)

Boron (B)

Bromide (Br)

Lithium (Li)

Dissolved solids

Specific 

conductance

(microsiemens

per centimeter 

at25°C)

Date

Well H-29, 

depth 54 

feet

37

210

59

570

34

0

21,611

290

300

1.6

.058

2.3

1.1

2.1

2,260

23,200

10-24-73

Well H-30, 

depth 76-90 

feet

37

130

25

100

11

0

660

32

61

1.0

.005

.510

.3

.690

728

21,100

3-21-74

Spring H-31

24

19

44

720

66

154

1,550

150

120

9.1

.009

4.3

.4

2.2

2,080

22,700

9-24-73

Spring H-32

45

140

13

390

51

0

761

32

470

4.6

-

.710

~

~

1,520

22,200

1-17-73

Spring H-35

17

35

46

840

45

0

1,810

280

330

6.5

.004

4.0

1.0

~

2,500

3,660

5-25-73

Well H-33, 

depth 50 

feet

34

22

5

19

-

0

84

11

6

.7

-

~

-

-

134

140

5-08-73

2Measured in field.

54
(A)

EXPLANATION 

 WELL

"^ SPRING

CHEMICAL CONSTITUENTS

S04 Sulfate

Cl Chloride

Ca Calcium

Mg Magnesium

Na + K Sodium + potassium

C03 + HC03 Carbonate + bicarbonate

PERCENTAGE OF TOTAL IONS, 

IN MILLIEQUIVALENTS PER LITER

(B)

cc

UJ

DC 

UJ 

Q. 

CO

z

UJ

I

D 

o

LU

100

50

20

10

UJ 

O

O

o

0.5

0.2

0.1

Ca Mg Na + K Cl + F

CONSTITUENT

SO, C03 + HC03

EXPLANATION 

....... H-29

 H-30

 ---- H-31

 H-32 

----- H-33

Figure 27.--(A) Major-ion composition and (B) concentrations in five ground-water samples 

from Canon de San Diego near the rim of Valles Caldera.

55
Stream discharge data (not shown) indicate that the 

annual flood peaked in the first half of May. The rapid 

response of the aquifer to changes in river stage 

indicates effective hydraulic interconnection that must 

be higher than the altitude of the spring, a short 

distance upstream. Presumably the entrance to the 

water-yielding zone in limestone is less than the high 

stage of a large flood but out of reach of small floods 

(such as in 1974) and lower river stages. Tritium data 

(Trainer, 1978, table 8A) help support the 

interpretation that stream water enters the bedrock: the 

concentration of tritium in water from spring H-32 on 

March 8, 1973, was 18.8 ± 2.1 TU and on May 22, 

1973, was 75.0 ± 4.0 TU.

In an earlier study (Trainer, 1984) fluctuations of 

constituent concentrations in the mineral springs at 

Soda Dam and Jemez Springs, for which observations 

are available for random dates over periods of years, 

were studied by constructing plots of 2-month running 

median values of selected constituents and discharge. 

Such plots for spring H-32 and for the Jemez River 

below East Fork near Jemez Springs (08321500) (fig. 

29) generally repeat the pattern seen in figure 28. Cl 

and HCC>3 concentrations show the same relation 

shown in figure 28; however, the concentration of 804, 

in contrast, is rather stable during much of the 

fluctuation of the other constituents in the plot but 

increases conspicuously during recession from the 

spring-flood peak in the river. This behavior, plus the 

odor of H2S present most days in this fumarolic area 

(and present also in water from wells H-29 and H-30), 

suggests that part of the 864 in ground water has been 

produced in the aquifer by the oxidation of H2S rising 

through it:

H2S + 4H2O = 10H+ + 8e' (4)

(Hem, 1970, p. 161). Two hypotheses are suggested to 

account for the timing of the surge in 804 

concentrations: (1) the rise of ground-water level 

during an episode of recharge temporarily reduces the 

availability of H2S by retarding its upward movement, 

whereas the recovery of the dissolved-solids 

concentration during recession from the flood peak is 

accompanied by renewed oxidation of ^S and 

production of S04 and (2) widespread temporary 

saturation of the soil during melting of snow cover may 

interrupt the connection between soil and rock pores 

and the atmosphere, temporarily retarding the ascent of 

H2S through the unsaturated rock column. The second

explanation is thought the more likely because (1) 

concentrations of 804 are elevated at other sites 

downcanyon (discussed in a subsequent paragraph), (2) 

ground water at those other sites is not diluted by 

surface water, and (3) there is little if any recharge from 

land surface to cause dilution.

Test holes H-29 and H-30 were drilled into 

limestone at sites a few feet apart. H-29, 54 ft deep, 

penetrates a water-yielding zone at 50 ft. Hole H-30 

was finished with two pipes. One is open, from 76 to 90 

ft, to a water-yielding zone first penetrated at 85 ft. The 

other pipe extends to 200 ft, is capped at the bottom, 

and contains water from 118 to 200 ft. Water was 

placed in this second pipe to provide a medium in 

which to measure the temperature profile, but the water 

level in the pipe dropped to 118 ft, evidently because of 

a leak at that level. After this pipe was installed a 

concrete plug was set around it at 90 to 100 ft; the hole 

and wallrock are unsaturated from 100 to 200 ft. The 

thermal profile was measured in the 118- to 200-ft 

segment of water-filled pipe after the temperature 

around the hole stabilized.

The observed thermal gradient of 4 °C over a 66- 

ft range in depth in H-30 is equivalent to 6.1 °C per 100 

ft, a high near-surface gradient even in a geothermal 

region. If the thermal conductivity of the limestone is 

assumed to be 6 x 10"3 cal/cm sec °C (Clark, 1966, p. 

462), the heat flow implied by the observed gradient is 

about 12 HFU. If the thermal profile continued 

downward at the observed gradient, the boiling point 

(about 93 °C at 6,000-ft altitude) would be reached at a 

depth of about 1,080 ft. The top of the limestone is 

about 250 ft above land surface near H-30. If the total 

thickness of limestone were about 1,200 ft, as in wells 

GT-2, PC-1, and VC-1, the base of the formation would 

be about 900 ft below land surface at the well site. 

These figures suggest that the deep conduit is in the 

basal limestone, in the upper part of the crystalline 

rock, or both. Perched ground water in each wateryielding zone above the geothermal conduit(s) sweeps 

away part of the heat carried upward by conduction 

through unsaturated rock and by convection (in vapor) 

through fractures. Any additional perched water in the 

section beneath test hole H-30 would add to the 

uncertainty. The cumulative effect of all such wateryielding zones on heat flow to the surface cannot be 

estimated from the data available.

56
cc111

°- 400

cc 

o

Zi 0

40 2 

CC 

UJ 

Q_ 

W

0 O

1973

400

BICARBONATE

DISCHARGE ' '

UJ

o

I

o

o

0

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

1974

Figure 28.--Fluctuations in bicarbonate and chloride concentrations and discharge of spring H-32 

located near the rim of Valles Caldera, 1973-74.

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

Figure 29.--(A,B) Fluctuations in concentrations of selected ions in spring H-32 and (C) streamflow 

discharge at Jemez River below East Fork, near Jemez Springs (08321500). Point 

plotted January 31 is median for all samples collected in January or February; point 

plotted February 28 is median for February and March samples; and so on.

57
Selected variables also were measured 

periodically in wells H-29 and H-30, although the test 

drilling was not completed until late 1973. The record 

available (fig. 30) is similar to the 1974 record for 

spring H-32 (fig. 28); the principal exception is timing 

of the maximums/minimums in variables during the 

spring flood. During 1974 the spring flood at Jemez 

River below East Fork, near Jemez Springs peaked in 

late March. As discussed earlier, well H-30, and 

possibly well H-29, may tap the outer edge of the 

ground-water mound beneath the Jemez River. 

Differences in potentiometric levels and water 

chemistry indicate that the water-yielding zones tapped 

by wells H-29 and H-30 are hydraulically separated, 

but this is unlikely if both water-yielding zones are in 

contact with the recharge mound beneath the river. The 

content of geothermal indicator ions in both well 

waters indicates that both water-yielding zones receive 

inflow and dissolved loads from a source of mixed 

water. The most plausible explanation for the data in 

figure 30 is that each well taps a zone containing mixed 

water and that, at least during the spring flood, each 

zone is open to the river upstream through channels in 

the limestone sufficiently near the well site to explain 

the rapid response shown in the hydrographs. The 

setting probably is similar to that for spring H-32 (fig. 

28) but with less effective connection to the stream. 

The water-yielding zones in all limestone springs and 

wells described in the foregoing paragraphs are thought 

to consist chiefly of interconnected bedding-plane 

openings.

The coincidence of fumarolic H2S and high 

concentrations of 804 in well and spring water in the 

canyon near the caldera rim suggests the hypothesis 

that part of the SO4 in ground water is produced locally. 

Data to support this hypothesis are summarized in 

figure 31. The trend line in figure 31A was drawn using 

the data for caldera wells, well VC-1, and springs H-6 

(Soda Dam) and H-14 (Jemez Springs), all of which 

represent either geothermal reservoir or derivative 

water. As extended toward the lower left this line fits 

fairly well the upper part of the distribution field for all 

other wells and springs, most of which are situated in 

or near Canon de San Diego. Some samples are 

believed to contain a geothermal component (D-6, H29, H-30, H-31, H-32, and H-35 and perhaps E-7 and 

H-21); other samples do not (H-39, H-42, and P-12). 

Other samples may contain a geothermal component, 

but the data are not fully convincing. However, figure 

3 IB shows that many of the samples in the canyon

proportionately contain more SO4 than the caldera well 

samples. By taking dilution into account, several 

waters (VC-1, H-6, H-14, H-29, H-31, H-32, H-35) 

contain larger concentrations of SO4 than most or all of 

the caldera well samples.

High concentrations of SO4 in ground water 

have rarely been detected in the southwestern Jemez 

Mountains outside Canon de San Diego. Data for five 

springs were summarized for comparison with the data 

shown in figure 31B. Purtymun and others (1975,1976, 

1978) monitored a native-water spring that drains 

volcanic rocks in Lake Fork Canyon (fig. 31C); the 

median of 26 Cl analyses is 4 mg/L, and the median of 

25 SO4 analyses is 4 mg/L. Two springs in Church 

Canyon, a few hundred yards east of Jemez Springs, 

issue from volcanic rocks at their contact with Abo 

Formation sandstone. Median values for 27 composite 

samples from these springs (Purtymun and others, 

1975, 1976, 1978) are 6 mg/L for Cl and 8 mg/L for 

SO4. Twenty-seven samples from Sino and Agua 

Durme Springs (Purtymun and others, 1975, 1976, 

1978; Shevenell and others, 1987) near VA-136 (fig. 

31C) have median values of 4 mg/L for Cl and 3 mg/L 

for SO4.

These springs are unlikely to yield water 

containing high SO4 concentrations because they are 

isolated from the Canon de San Diego ground-water 

system either by distance (Lake Fork Canyon) or by 

geohydrologic setting (Church Canyon; Sino and Agua 

Durme Springs). No data are available in the study area 

to demonstrate SO4 concentration in local limestone 

outside the Cafton de San Diego flow system. Thus, the 

tentative conclusion that high SO4 concentrations (fig. 

3 IB) reflect local oxidation of fumarolic H2S cannot be 

fully tested. This topic is considered further in the 

following discussion of the mineral springs at Jemez 

Springs and Soda Dam.

Jemez Springs and Soda Dam

The springs at Jemez Springs issue from 

alluvium beside the Jemez River, but the water comes 

from underlying bedrock. The areal distribution of 

some of the springs suggests that their source is 

fractures within the underlying bedrock. Several of the 

springs, which maintain their positions even after 

submergence by flooding, are probably the outlets of 

travertine-lined tubes in the alluvium. Others are 

constructed; one appears to be a dug well lined with 

stones and another the outlet of a tile drain.

58
1,700

£ 1.600 

.1- 

Z _i 

O II. 1,500

ii M0°

01 S

g2 1,300 §i

I 300

200

H Ol

UJO .. Uj< 42

o. o,

Z <r

~-« 43

iu Q > z

33 44

£g

5 3 45 

> Ol > m

a 700

^a eoo

ff U

500

"o

100 ' ^

Z 0 

:^ 67

LU Q

s

I i I I I \ \

BICARBONATE

I I I I I i i l I

WATER LEVEL

MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

WELL H-29

BICARBONATE

CHLOR|IDE

WATER LEVEL

APR MAY JUNE JULY AUG SEPT OCT NOV DEC

WELLH-30

Figure 30.-Ion-concentration and water-level fluctuations in wells H-29 and H-30,1974.

At Soda Dam, spring flow issues from fractured 

limestone and gneiss in the floor of Cafton de San 

Diego at a point where one section of the Jemez Fault 

separates (fig. 5) and bounds a horst, forming a hill 

above the canyon floor. That section of fault continues 

through the mesa west of Jemez Springs. Another 

seemingly separate section of fault extends 

southwestward beneath the village but is concealed 

farther south beneath canyon-floor deposits.

A test well at Jemez Springs was drilled to a 

depth of about 800 ft. Goff and Kron (1980) presented 

a lithologic log of the well, and Goff and others (1981) 

provided additional geologic information about the log 

and chemical and isotopic analyses of water samples. 

The well penetrated, in descending order, about 70 ft of 

gravel, 700 ft of limestone and sandstone, and 60 ft of

gneiss. Water was noted at several levels within the 

gravel. Confined thermal water was found at the 

alluvium-limestone contact and at about 500 ft in 

fractured shale within the Madera Limestone. No water 

was present at the top of or within the gneiss.

Numerous measurements of discharge of single 

springs at Jemez Springs and Soda Dam ranged from 

less than 1 to 72 gal/min. Measurements of individual 

springs are not representative of an entire group of 

springs, however, because many springs are located 

within the streambed. Summers (1976, p. 36-37) 

concluded that total spring flow at Soda Dam, as 

indicated by increased streamflow, was 0.6 ft3/s (about 

268 gal/min) on August 2, 1949.

59
1UU

10

1

0.1

. 1 1 1 1 1 1 1 1

: (A)

-

-

;

-

: H-40. 

: P-7-

- H-41

,''

: ,'

- ,'' D-4

- P-1£' 

'. ,'' .Q-4

/' .G-3 .H-39

i i ,11111

,'

x4° 'ff . O

x x H-28 D*6 '

Xn-4 -A-8

 H-3

.VA-136

G^T^H-42

i i ii,,,,

BA<

VC-1

f 'i

H-31 yf^''

x''.H-29

X ''*H-21

.E-7

 H-32

A-9

 H-32

WC23-4,''

VC-2Ax'«VC-2B

=A13 .%ACA15 '

,--H-6 BACA4

H-14 :

^VC-1 -

i

-

0.01 

1 10 100 1,000 10.C

50

10

(B)

D-4 

H-41. '

H-40

P;7

 G-3 ' H '3'9

D-6

^"

H.-3H-4 A'9'

A"8 H-30

.VA-136

 G-1

 H-28

H-42

H-35

H-31

E-7

VC-1<*

H-14 

B,

H 32^-~" Bfi

H-6 .VC-2A :

 BACA13 : 

VCA4 

CA15- WC23-4 '

VC-2B :

1 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

106°50'

10 100 1,000 10,000 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

106°30'

-6,VA-5,VA-27

Jemez 

Springs

H-21

R.1 E. R.5E.

10 MILES

0 5 10 KILOMETERS

Figure 31 .--(A) Chloride and boron and (B) chloride and sulfate in water from wells and springs

in the Valles Caldera and Canon de San Diego area and (C) map showing location 

of wells and springs (data from Purtymun and others, 1975, table II; Trainer, 

1978, table 5; White, 1986, table 1; Shevenell and others, 1987, table B-ll; and Goff 

and others, 1988, table 2, and 1992).

60
In five of six measurements made in 1973 

(table 9), a net loss in stream discharge occurred in the 

reach passing Soda Dam. Because the downstream set 

of measurements was made about 1,000 ft below the 

dam, the decrease in discharge may be due to 

infiltration into the streambed beginning just 

downstream from the sill formed by the dam. Similar 

measurements upstream and downstream from the 

group of visible springs at Jemez Springs were 

inconclusive.

Another method used to estimate total spring 

flow requires only two streamflow measurements and 

determinations of Cl concentration for the two groups 

of springs: one set of measurements downstream from 

each group of springs. (This is possible because 

chloride concentration in the river upstream from Soda 

Dam is so small as to be negligible.) Total spring 

discharge at Soda Dam is proportional to chloride load 

in the stream downstream from the dam. At Jemez 

Springs, total spring discharge is proportional to the 

difference in chloride loads downstream from the two 

groups of springs. Measurements during January 1973- 

September 1974 showed the minimum discharge of the 

Soda Dam Springs (not including loss to infiltration) to 

range from 111 to 1,046 gal/min; the median of 46 

measurements was 365 gal/min. Corresponding values 

at Jemez Springs ranged from 48 to 1,538 gal/min; the 

median of 43 values was 333 gal/min. The largest

values are thought to be in error beyond those due to 

infiltration because wading measurements could not be 

made at high river stages, and therefore discharge 

values for the Jemez River below East Fork Jemez 

River (08321500, fig. 6) had to be used as estimates. 

The conclusions from the limited data are that 

discharge from each group of springs is several 

hundred gallons per minute most of the time and that 

spring flow widely fluctuates with time.

Representative chemical data for Jemez Springs 

and Soda Dam are listed in table 10. Water at both 

locations has a Na Cl composition and large 

concentrations of Ca and HCO3. The ratios Li/Na, 

Li/Cl, and B/C1 are in the ranges found by White 

(1957) to be typical of volcanic waters. The water at 

Soda Dam is nearly twice as mineralized as that at 

Jemez Springs. Conversely the Jemez Springs water is 

hotter about 75 °C compared with about 45 °C at 

Soda Dam. Both groups of springs emit H2S and 

exhibit temporal fluctuations in dissolved solids. Both 

groups have individual springs that appear to be 

affected by dilution with native ground water.

Plots of typical analyses of mineral water from 

Jemez Springs and Soda Dam are shown in figure 32. 

Also in this figure are reconstructed analyses that 

assume simple dilution of parent reservoir fluid(s) 

without dissolution of wall rock in flow conduits or 

other additions of dissolved ions. The large increases in

Table 9. Discharge of the Jemez River upstream and downstream from Soda Dam 

[Location of Soda Dam shown in figure 6]

Discharge, in cubic feet per second

Date

Upstream from 

Soda Dam

1,000 ft

downstream from 

Soda Dam Difference

2-23-73

3-20-73

3-28-73

4-06-73

7-02-73

7-13-73

14.1

22.8

33.0

18.8

16.4

24.9

9.47

22.7

29.5

21.0

15.6

23.2

-4.6

-0.1

-3.5

+2.2

-0.8

-1.7

61
20

10

5

2

1 

0.5

0.2

0.1

0.05

0.02

0.01

0.005

0.002

0.001

Spring H-6 

12-1-1972

.Spring H- 14

 12-2-1972 .7

Spring H-6 ./ 

(reconstructed) -i

Spring H-14 "/ ' 

(reconstructed)

Ca Mg Na+K+Li CI + F+Br 

CONSTITUENT

SO4 CO3 + HCO3

Figure 32.--Actual and reconstructed concentrations of major ions in water from spring H-6 at

Soda Dam and spring H-14 at Jemez Springs, 1972. Reconstructed concentrations 

are based on the assumption of simple dilution of reservoir fluid. Spring locations 

shown in figure 31C.

concentrations of Ca, Mg, and HCO3 in each pair of 

graphs represent dissolution of limestone by flowing 

thermal water. There seems to be no readily soluble 

source of Na, K, and Cl along flow paths outside the 

caldera, and these constituents in addition to Li, F, and 

Br act conservatively. An unexplained aspect of each 

pair of plots is the difference in SO4 content, noted 

earlier and considered further in a later discussion.

The samples represented in table 10 were 

selected in part to illustrate the considerable range in 

concentrations typical of mineral water at Jemez 

Springs and Soda Dam. The degree of dilution during 

mixing of the fluids can be estimated with the massbalance equation used in earlier sections of this report. 

For example, using the more concentrated sample from 

spring H-14 in table 10 and assuming ground water 

from Baca 4 (1,991 mg/L Cl) and VC-2A (2,943 mg/L 

Cl) as parent reservoir fluids indicate dilute-water to 

thermal-water volume ratios of 1.2:1 for Baca 4 

reservoir fluid and 2.2:1 for VC-2A reservoir fluid 

(table 11). Because of uncertainty over the identity of 

geothermal and dilute parent water, these calculated 

mixing proportions need to be considered estimates.

Fluctuations in Constituent Concentrations

Review of the series of analyses of mineral water 

from Jemez Springs and Soda Dam shows that the 

water has maintained its typical chemical character 

over the period represented by "modern" analyses at 

least since the study by Kelly and Anspach (1913). 

Concentrations of constituents have shown substantial 

fluctuation, however.

An approach to analyzing fluctuations in 

concentration, used in an earlier study (Trainer, 1984) 

and in the previous discussion of spring H-32 (fig. 29), 

consists of summarizing analytical data by month of 

sampling. Even with the large data set now available, 

however, some monthly subsets contain only a few 

samples and hence may be less representative than 

other subsets. This problem was addressed by 

summing the data in 2-month subsets to increase 

sample size and plotting 2-month running median 

values monthly (for example, January-February 

median plotted on February 1, February-March median 

plotted on March 1, and so on). The resulting runningmedian curves are shown in figure 33. For streamflow, 

mean monthly values were used instead of medians 

because of easier computation and the large amount of 

available data.

62
Table 10. Chemical analyses of mineral water from wells and springs at Jemez Springs an

[Date shown indicates when sample was collected; quantities in milligrams per liter except specif

(microsiemens per centimeter at 25 degrees Celsius (°C)), temperature (°C), and pH (pH units)

Unnumbered analyses by U.S. Geological Survey; VA analyses from Shevenell and others, 198

Spring H-14 (Travertine 

Mound), Jemez Springs

Constituent

Silica (SiO2)

Calcium (Ca)

Magnesium (Mg)

Sodium (Na)

o> Potassium (K) 

w

Lithium (Li)

Bicarbonate (HCO3)

Sulfate (SO4)

Chloride (CD

Fluoride (F)

Boron (B)

Bromide (Br)

Dissolved solids

Specific conductance

Temperature (°C)

pH

12-02-72

79

130

5

640

82

8.7

732

53

920

4.8

7.4

4.8

3,500

3,930

75

6.3

VA-7 

1- -79

93

182

4.56

614

75.2

8.20

723

36.1

829

5.21

7.8

-

-

4,200

70

6.28

Geothermal well, 

Jemez Springs

VA-191 

1-19-79

70

122

5.76

546

61.6

6.96

642

45

705

4.42

6.1

-

2,220

3,300

68

6.64

VA-152 

1-19-79

24

120

9.31

185

29.9

2.27

479

38

243

3.3

2.2

-

1,140

1,700

60.5

6.69

Well H-17, 

Jemez 

Springs 

5-30-74

71

160

7

510

63

7.8

760

43

700

4.4

7.4

3.0

1,960

3,600

58

7.1

Buddhist 

Spring, 

Jemez Springs 

VA-8 

1- -79

81

154

9.57

458

53

7.56

697

37.6

653

3.86

5.7

-

2,160

3,300

49

6.38

Spring H-6, Main Spring, Soda D

VA-26

5- -79

46

429

21.4

920

177

13.6

1,490

49.4

1,460

3.57

12.8

-

4,630

6,600

47

6.52

12-01-72

50

330

24

990

200

13

1,578

52

1,500

3.3

12.5

6.9

3,740

8,000

48

61

VA-7

10- -

48

346

24.

840

186

13.

1,500

36

1,570

3

8

5

4,539

6,700

47

6

1VA-19 at contact of alluvium and Magdalena Group at 80 feet; analysis from Goff and others (1982, table 

2VA-15 in fractured shale, Magdalena Group at 500 feet; analysis from Goff and others (1982, table 1).

1).
(A) 1,600

CHLORIDE 

SPRING H-6 AND GROTTO SPRING, VA-5, AT SODA DAM

1,000

900

't 800 o-*

O 1

700

;3 eoo

/CHLORIDE

BICARBONATE 

: SPRINGS H-14 AND H-15 AT JEMEZ SPRINGS

UJ<

S 

o

2

3 200

_J

5 40

30

20

400 -

SPRING H-32 NEAR BATTLESHIP ROCK

(B)

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

oc oc i- in

co a.

JEMEZ RIVER BELOW EAST FORK, 

NEAR JEMEZ SPRINGS

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

Figure 33.-Fluctuations in (A) 2-month running median concentrations of selected ions in springs, 

1973-86 and (B) mean monthly streamflow in the Jemez River below East Fork, near 

Jemez Springs (08321500), 1963-76.

64
Table 11. Example of degree of dilution calculated for typical mineral-water samples 

from Jemez Springs and Soda Dam using two assumed parent reservoir fluids

[Locations shown in figure 31C. Data from Trainer (1978, table 5), White (1986, table 1), Shevenell and

others (1987, table B-II), and Goffand others (1988, table 2). Dilution is characterized

as the volume of dilute water that, when mixed with one volume of reservoir fluid, would

produce a mixture like the measured mineral water. mg/L, milligrams per liter]

Mixed water

Parent 

reservoir

fluid, sample 

date, and 

chloride

concentration

Spring H-14, Jemez Springs

12-02-72, 1-79, 

Cl, 920 mg/L Cl, 829 mg/L

Spring H-6, Main Spring, 

Soda Dam

10-81, 5-79, 

Cl, 1,570 mg/L Cl, 1,460 mg/L

Baca 4, 

6-11-82; 

Cl, 1,991 mg/L

VC-2A 

8-27-87; 

Cl, 2,943 mg/L

1.2 volumes

2.2 volumes

1.4 volumes

2.6 volumes

0.3 volume

.9 volume

0.4 volume

1.0 volume

The water-chemistry plots in figure 33 illustrate 

two different settings. Spring H-32 responds rather 

promptly to periodic dilution by stream water. The 

plots for Soda Dam and Jemez Springs also are best 

explained by periodic dilution but at a greater distance 

from the source, so the effect takes longer to be seen at 

the springs.

The Cl plot for spring H-32 shows a major 

decline in concentration because of dilution by river 

water during the snowmelt flood, a long period of 

recovery while the river water drains from local 

ground-water conduits in the limestone, and a period 

during which the native ground-water regime is 

dominant. The reason for the peak concentration in 

October-November is unknown. The HCC>3 plot, 

generally similar to the Cl curve, shows the same 

pattern of dilution and recovery; its consistent slope in 

late autumn suggests that the sharp peak in Cl is 

anomalous. The SO4 plot is basically featureless except

for a slight decline during the snowmelt flood and an 

increase after it. This pattern and the concentrations 

involved were attributed to production of SO4 in the 

aquifer from I^S ascending from below and temporary 

suppression of the process during the flood and 

recovery afterward. Analyses for water from Baca 

wells indicate Cl concentrations of about 1,900 to 

2,500 mg/L and SO4 concentrations of 35 to 42 mg/L 

(see table 6). For spring H-32 the corresponding values 

are about 400 mg/L Cl and about 30 mg/L SO4. As 

noted earlier, flood water is believed to move into the 

aquifer locally, and the influence of the flood-produced 

recharge is the dominant control reflected on the 

chemical hydrographs.

The annual fluctuations in Cl and HCO3 at Soda 

Dam are quite different. Conservative Cl 

concentrations decline in April-May and in AugustSeptember, whereas nonconservative HCC>3 

concentrations increase during these two periods,

65
perhaps because of enhanced dissolution of rock in 

conduit walls by the more dilute (undersaturated) 

water. The annual pattern for SO4 is generally 

featureless except for a peak after a major episode of 

dilution. The two annual minimums for Cl were found 

in an earlier study (Trainer, 1984, fig. 5) and explained 

as effects of dilution with a lag time that is dependent 

on the time required for flow from the site of dilution. 

In that study the Cl minimums were correlated with 

two regional events, the snowmelt flood in spring and a 

much lower streamflow peak that occurs in many years 

during September-November. Review of streamflow 

data shows the autumn peak to be smaller and less 

frequent than was earlier thought, and in light of the 

additional data presented here an alternate explanation 

is thought more likely. Both Cl minimums at Soda Dam 

reflect the snowmelt flood. The August-September Cl 

low, with its associated SO4 peak (by analogy with 

spring H-32) followed by the maximum mean Cl 

concentration, represents dilution at a site that requires 

at least 4 months travel time to Soda Dam. The AprilMay Cl low and its associated HCC>3 peak represent 

dilution at a site within a few weeks' travel time of 

Soda Dam and in a reach of the canyon floor/fault 

system where relatively little 864 is locally produced. 

Because the cavernous nature of conduits in the 

limestone facilitates relatively rapid flow, the AugustSeptember dilution can be most likely correlated with 

the snowmelt flood of the same year (a 4-month lag) 

rather than with a flood of an earlier year (lag time 16 

months, or 28 months, and so on). Specific dilution 

sites cannot be identified, although a distant site in the 

region from the ring fracture to the area of fumaroles 

near Battleship Rock and a proximal site nearer Soda 

Dam seem to be consistent with available data.

The running-median Cl plot for Jemez Springs 

(fig. 3 3 A) shows decreases in April-May, July-August, 

and October-November. Thus, the water at Jemez 

Springs appears to have had a more complex dilution 

history than that at Soda Dam a conclusion that is not 

surprising because of the greater degree of dilution of 

the Jemez Springs water (table 11).

Covariation of SO4 and Cl (fig. 34) provides 

another means of studying the mineral water. Chemical 

and isotopic data for individual wells in the Redondo 

Creek reservoir (Truesdell and Janik, 1986, tables 1,3; 

White, 1986, tables 1, 3) show considerable variation, 

which White (1986, p. 1855) suggested may be due to 

production testing.

Plots B, C, and D (fig. 34) also exhibit linear 

distributions of data. Many of the data points are 

spaced sufficiently close in time to show the sequential 

change in the relation of 864 to Cl (plots Bl, Cl, and 

Dl) over short periods; the patterns of these changes 

support the general trends of the lines in corresponding 

plots B and D. These three diagrams represent three 

different variants of the pattern for the geothermal 

reservoir(s) (plot A).

The chief factors controlling plots B, C, and D 

are believed to be the rate of production of 864 and the 

dilution of fluid by mixing. Goffand others (1981, p. 

239) identified three sources of SO4 in this region: 

oxidation of H2S rising from the heat source in the 

caldera, oxidation of pyrite (FeS2) present in 

crystalline and sedimentary rocks, and reaction of 

thermal water with organic sulfur in carbonate rocks 

and shale. Earlier discussion in this report concluded 

that local oxidation of H2S, which rises from thermal 

water at depth and enters perched ground water, 

explains the anomalous areal pattern and 

concentrations of SO4 in ground water in Canon de San 

Diego.

Spring H-32 (plot B), near the caldera rim, 

displays a linear pattern similar to those for several 

Baca wells. Periodic mixing with dilute river water 

reduces the Cl content and thus explains the lower 

slope of the line. Despite its smaller Cl content, spring 

H-32 water contains as much SO4 as water from many 

of the Baca well samples, believed to reflect local 

production of 804.

The plot for spring H-6 at Soda Dam, shown by 

inset C, is compared with that for Baca well water. 

After dilution, the spring water contains more SO4 than 

the Baca water in proportion to other constituents and 

as much as many of the other constituents. The mixed 

water evidently has received an appreciable SO4 input 

since the geothermal water left the caldera reservoir(s).

The water in spring H-32 and spring H-6 

represents moderate and small modifications, 

respectively, of the reservoir fluid(s); the water in 

spring H-15 at Jemez Springs, however, greatly differs 

with respect to SO4/C1: the slope of the trend line (fig. 

34, inset D, solid line) indicates direct covariation of 

SC>4 and Cl rather than inverse covariation as in plots A, 

B, and C. Direct covariation implies a much smaller 

input of 804, if any at all, since the last major episode 

of dilution of the Jemez Springs. Local dilution, 

indicated by the dashed trend lines in figure 34D, is 

considered in subsequent discussion.

66
C1

SODA DAM DATA FIELD

SODA DAM DATA FIELD

60

SPRING H-32 DATA FIELD

CHLORIDE CONCENTRATION, If MILLIGRAMS PER LITER CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

NOTE: ALL DATA ARE WITHIN THE

COORDINATE FIELD SHOWN. 

DASHED RECTANGLES SHOW 

PARTS OF COORDINATE FIELD 

PLOTTED SEPARATELY FOR 

CLARITY.

JEMEZ SPRINGS 

DATA FIELD SODA DAM 

DATA FIELD

SPRING H32 

DATA FIELD

1,600

500 1,000\ 1,500 2,000 2,500 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

B

SPRING H-32 DATA FIELD \ D

JEMEZ SPRINGS DATA FIELD

3,000 3,500 Q-j

JEMEZ SPRINGS DATA FIELD 

50

zee 

OLU

fCCC 

tlltl 2.tL

60

40

20

DZ~

Spring H-32

60

Zee OLD

z.aDZ

Jemez Springs

Depth. 

79 v

Depth/0 feet \~-t~" 

499 \ _-.-- ' * ' feet V '

'A

 SPRINGS H-14 AND H-15 

x OTHER WELLS OR SPRINGS 

o GEOTHERMAL TEST WELL

_______I___________

zee 

O Hi

§40

~

1-79

0 500 1,000 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

30

SPRING H-15

3-82

1-79

10-85

1-83

500 1,000 900 950 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

1,000

Figure 34.--Covariation of sulfateand chloride in reservoirfluidsand in mineral water from the 

VallesCaldera and Canon deSan Diego (data from Purtymun and others, 1975, 

1976,1978,1980a,b, and 1981; Trainer, 1978; White, 1986; and Shevenell and 

others, 1987). Wells and springs shown in figures 5 and 31.

67
Stable-isotope data also are valuable evidence of 

dilution and mixing of water. Isotopic and chloride data 

are listed in table 12, and the covariation of the stable 

isotopes deuterium and 18O for fluid samples from 

geothermal reservoirs and Canon de San Diego as far 

south as Jemez Springs is shown in figure 35. Data for 

wells GT-2, VC-1, VC-2A, and VC-2B also are shown 

in figure 35.

The deuterium content of rain and snow is 

temperature (and hence altitude) dependent; deuterium 

is lower at lower temperatures than at higher 

temperatures. Water becomes increasingly depleted in 

deuterium with increasing negative numbers. The 18O 

content of water can be affected by several processes, 

two of which are significant in a geothermal 

environment: the exchange of oxygen between rock 

and fluid, with the fluid becoming enriched in 18O 

(progressively smaller negative numbers), and 

evaporation (steam loss). The meteoric-water line 

shown in figure 35 was developed by Vuataz and Goff 

(1986, p. 1842), who used data for streams and for 

spring water of shallow circulation in the Jemez 

Mountains. Some groups of points for a single spring 

system show a linear distribution that defines the 

variation in the proportions of parent waters a 

dilution trend line between a reservoir fluid and a point 

on the meteoric-water line. Lines for the Jemez Springs 

and Soda Dam water are shown in figure 35. The 

isotopic composition of a mixed water situated on a 

dilution line can be computed from its distances from 

the geothermal-fluid and meteoric-water end members 

and from their isotopic compositions. A second useful 

aspect of a dilution line is the approximate isotopic 

composition of an unknown geothermal parent fluid. 

The dilution line for Jemez Springs, and perhaps that 

for Soda Dam water, supports geothermal parent fluids 

that are similar isotopically to the sample from well 

VC-2A in the Sulphur Springs reservoir (fig. 35).

©fog] OGI ©if MooKiirsil W®tt©ir

On the basis of published reports, investigators 

of the thermal waters in and near Valles Caldera believe 

that (1) mineral waters in Canon de San Diego are 

derivatives of the geothermal-reservoir fluids and (2) 

the available data and understanding of the entire 

regional hydrologic system are inadequate for a 

determination of where and how the mixed water was 

formed. This situation may not change substantially in 

the future because prospects for further exploration for

geothermal-energy development are uncertain and 

because much of the area is Federal, State, or Indian 

lands where other kinds of development are likely to be 

limited. For these reasons a general statement of origin, 

even if somewhat speculative, is desirable. The 

following discussion centers on three broad issues 

concerning mineral water: (1) the likely nature of a 

parent geothermal fluid; (2) possible source(s) of a 

dilute (mixing) water; and (3) the likely manner and 

place(s) of mixing. Because the mixed water is found 

in different geohydrologic settings for which different 

types or quantities of data are available, the discussion 

is organized by individual occurrences of mixed water.

W@IDs ©T=2, PC-1, aimcB PC=2

Goff and others (1988, p. 6049) suggested, on 

the basis of geographic proximity, that reservoir fluid 

from the Sulphur Creek area is the likely geothermal 

parent of derivative mixed water beneath the Jemez 

Plateau. This inference is supported by the analytical 

data for well GT-2.

Potential geothermal parent water for well GT-2 

can be examined on the basis of chemical and stableisotope data (figs. 22 and 36, respectively). In figure 22 

the linear distribution of chemical data suggests that 

either Baca (Redondo Creek) or Sulphur Creek 

reservoir water might be credible parent fluid(s), hence 

a Sulphur Creek geothermal parent, perhaps similar to 

the samples from wells VC-2A, VC-2B, or WC 23-4, is 

probable. (Two samples were collected from well WC 

23-4, at depths of 4,800 and 6,300 ft. Goff and others 

(1992) suggested that the deeper sample represents 

pore fluid in the crystalline rock. Only the sample from 

4,800 ft is suggested here as a possible reservoir fluid.) 

Interpretation of the isotopic data (fig. 36) confirms the 

choice of Sulphur Creek fluid, but only well VC-2A, of 

the three samples available, could be a parent fluid 

because of the isotopic compositions of the parent 

geothermal and dilute waters.

The distribution of geothermal-fluid samples in a 

commonly used plot of deuterium and 18O is illustrated 

in figure 56. Points for geothermal water are right of the 

meteoric-water line, a shift explained by fractionation 

of oxygen through exchange between water and the hot 

rock through which it flows. Silicate minerals are richer 

in 18O than meteoric water, so the exchange enriches 

the fluid in 18O and shifts a point on the plot to a larger 

number (a smaller negative number). Isotopically, a 

dilute water would lie on or near the meteoric-water 

line in figure 36.

68
Table 12. Isotopic and chloride data for mineral water from wells and springs 

at Jemez Springs and Soda Dam

[mg/L, milligrams per liter; --, no data. Data from Purtymun and others (1975, table II), Trainer (1978,

tables 5,8A, 8C), Vuataz and Goff (1986, table 1), White (1986, tables 1,3), and

Goff and others (1988, table 2; 1992, table 1)]

Site 

identifier 

(figs. 5 

and?) Source of sample

Sample1 

number

Stable isotopes Tritium 

(tritium

Date 5D (per mil) 818O (per mil) units)

Chloride 

(mg/L)

Jemez Springs

H-14

H-15

VA-92

VA-19

VA-15

VA-19

H-17

Travertine Mound

Main Spring

Buddhist Spring

Geothermal well, 

80-foot depth

Geothermal well, 

500-foot depth

Geothermal well, at 

well head

Abandoned private 

well

_

VA-7

VA-66 

VA-91 

VA-123

VA-10 

VA-18 

VA-93

VA-92

VA-19

VA-15

~

~

12-02-72

2-21-73

1-79

12-80 

3-82 

1-83

1-79 

1-79 

3-82 

10-04-85

3-82

1-79

1-79

1-83

5-30-74

-82.1

-83.6

-83.1

-82.3 

-81.4 

-82.1 

-81.9

-83.6

-84.0

-85.9

-85.2

-10.52

6.4

-11.30

-11.35 

6.7 

2.92

-10.60 

-10.40 

-10.40 

-10.46

-11.05 10

-11.30

-11.80

3.58

-11.42

920

880

829

910 

869 

906

904 

968 

926 

917

617

705

243

862

700

Soda Dam

H-6

VA-5

H-6

Main Spring

Grotto Spring

Hidden Spring

-

~

VA-6 

VA-51 

VA-64

VA-89 

VA-99 

VA-109

VA-132 

VA-140 

VA-5

VA-27 

VA-90 

VA-110

12-01-72 

2-21-73

12-04-74

7-78 

4-80 

4-80

3-82 

9-82 

1-83

5-83 

2-01-84 

7-78

5-79 

3-82 

11-83

-84.8

-

-84.9 

-85.4 

-85.2

-84.0

-84.9 

-84.6

-84.9 

-85.1

-10.40 

4.0

.4

-10.60 

-10.70 

-10.60

2.9 

1.33 

-10.35 1.48

1.62 

-10.56 

-10.65

-10.95 

-10.65 5.7 

3.63

1,500

1,460

1,480 

1,520 

1,560

1,480 

1,614 

1,536

1,477 

1,480 

1,480

1,195 

1,240 

1,294

69
Table 12. Isotopic and chloride data for mineral water from wells and springs 

at Jemez Springs and Soda Dam Concluded

Site 

identifier 

(figs. 5 

and 7)

H-6

Source of sample

Jemez River above

Soda Dam

Sample1 

number Date

4-80

3-82

1-83

5-83

Stable isotopes

8D (per mil) 818O (per mil)

-94.4

-89.5

-

-85.4

-13.20

-12.50

-

-12.00

Tritium 

(tritium Chloride 

units) (mg/L)

4.0

13 19.5

11.8 10.3

32.6 11.3

Wells in Redondo Creek reservoir(s)

4

13

15

19

20

24

Baca4

Baca 13

Baca 15

Baca 19

Baca 20

Baca 24

7-09-81

7-09-81

7-02-82

3-30-81

8-12-81

8-13-81

6-04-82

7-01-82

9-08-82

9-08-82

10-82

10-23-80

10-25-80

8-13-81

8-13-81

7-15-82

7-16-82

-86

-87

-86

-90

-87

-89

-86

-83

-84

-82.2

-83.1

-87

-86

-85

-85

-79

~

-10.21

-10.23

-10.4

-10.19

-10.23

-10.34

-10.0

-10.2

-8.7

-8.7

-8.41

-9.21

-8.47

-9.48

-9.48

-8.90

-

_.

.49 1,981

1,897

2,019

.22 2,093

.47 2,678

.47 2,665

2,207

-

.91

2,458

Wells in Sulphur Creek reservoir

VC-2A

VC-2B

WC 23-4

VC-2A

VC-2B

WC 23-4 (4,800 feet)

8-27-87

VC2B-90 M7-90

VA-113 1-04-83

-74.4

-85.2

-80.4

-7.1

-7.5

-7.80

.47 2,943

.77 4,150

4,350

Sample numbers from Goff and others (1988,1992).

70
-70

-75

Q -80

UJtD 

LU 

Q 

<

-85

-90

-95

Dilution line for 

Jemez Springs 

(H-14andH-15)

VC-2B

Dilution line for

Soda Dam Springs

(H-6 and Grotto Spring)

20

EXPLANATION

® RESERVOIR SAMPLE--Baca wells 

identified by number only

+ SPRINGSH-14ANDH-15AT 

JEMEZSPRINGS

A GEOTHERMALTESTWELLVA-15 

AND WELL H-17 AT 

JEMEZSPRINGS

D BUDDHISTSPRINGAT

JEMEZ SPRINGS, VA-92

O SPRINGH-6ANDGROTTOSPRING, 

VA-5 AT SODA DAM

Hi HIDDEN SPRING AT SODA DAM, 

VA-27

H WELLVC-1 

® WELLGT-2

"-14 -13 -12 -11 -10 -9

DELTA OXYGEN-18 ((5 18O), IN PER MIL

-8 -7

Figure 35.-Covariation of deuterium and oxygen-18 in Valles Caldera reservoir fluids and in 

derivative mixed waters (data from Trainer, 1978; Truesdell and Janik, 1986; 

Vuataz and Goff, 1986; White, 1986; Shevenell and others, 1987; and Goff 

and others, 1988 and 1992). Well and spring locations shown in figures 5, 7, 

and 31.

-70

-75

-; -80

-85

-90

-95

VC-2A

GT-2

24

24. 

24® 19

24 /5

20*

.WC23-4, 

4,800 feet

 VC-2B

®20

'20

13

-13 -12 -11 -10 -9 -8 

DELTA OXYGEN-18 (<5 ieO), IN PER MIL

EXPLANATION 

® AVERAGE OF SEVERAL SAMPLES SHOWN

-7 -6

Figure 36.-Covariation of deuterium and oxygen-18 in water from geothermal wells in 

Valles Caldera and wells VC-1 and GT-2 near the caldera rim (data from 

Trainer, 1978, table 8C; Truesdell and Janik, 1986, table 3; Goff and 

others, 1988, table 2, and 1992, table 1). Well locations shown in figure 5.

71
Based on regional geohydrology, two aquifers 

are the likely sources of the dilute parent of the fluid in 

well GT-2. The first and more probable source, because 

well GT-2 is very near the rim of the caldera, is 

alluvium in the moat, recharged by infiltration from 

San Antonio Creek. In such a setting dilute water is 

thought to percolate downward to mix with laterally 

escaping reservoir fluid, with the resultant mixture 

moving into sedimentary strata of the Jemez Plateau, 

where the strata abut ring-fracture faults. Observations 

made during drilling of test holes showed the presence 

of cavernous zones near the base of the limestone. 

During normal ground-water circulation, such zones 

would have been opened along favorable joints and 

bedding-surface openings before the caldera was 

formed. The zones probably were later selectively 

enlarged, at and below the water level in flow channels 

from the reservoir, by the CC^-rich thermal fluid.

The second likely source of the dilute parent of 

the fluid in well GT-2 is ground water in perched zones 

in the section of volcanic and sedimentary rocks. Such 

zones were not identified during construction of well 

GT-2 because caving problems dictated rapid drilling, 

but one zone in volcanic rocks in a well drilled at the 

Fenton Hill site (fig. 10) for water supply (Becker and 

others, 1981) seems to have a continuing yield 

adequate to provide for the perennial flow of mixed 

water. Wells PC-1 and PC-2 (fig. 5) penetrate a 

volcanic and sedimentary section similar to that 

penetrated by well GT-2, and both pass through 

perched saturated zones containing dilute water. Some 

of these zones in lower Abo Formation and upper 

Madera Limestone rocks yield slightly mineralized 

water that may be very dilute mixtures of native ground 

water and geothermal fluid. Well PC-1, which extends 

completely through the sedimentary rocks into the 

underlying gneiss, also penetrates several wateryielding zones in the lower part of the limestone that 

yield mineral water similar to that in well VC-2A. 

Thus, although what may be very dilute mixtures are 

found far up in the section, the true mineral water is in 

the basal limestone as it is in well GT-2. As can be seen 

in figure 37, these deeper waters for PC-1 are more 

mineralized (less diluted) with increasing depth. Well 

records do not establish the five sampled horizons near 

the bottom of PC-1 as hydraulically separate wateryielding zones, but assuming that they are separate 

zones is reasonable; one was identified as a fracture and 

one as a cavernous zone (Shevenell and others, 1988, 

p. 16). The stacked nature of the assemblage indicates 

probable stratigraphic control of water-yielding zones,

in contrast to the strong structural control evident in 

hole VC-1. The stepwise-upward increase in degree of 

dilution suggests inflow of dilute water from above, 

wherever the dilution occurred, and the deeper and 

presumably more effectively isolated zones 

experiencing the least dilution.

Perched water-yielding zones in sedimentary 

rocks beneath Jemez Plateau are thought to be 

recharged by (1) infiltration through the beds of small 

streams on the plateau, many of which carry water only 

during and shortly after storms or (2) lateral flow into 

the sedimentary strata from ground water in the moat, 

as outlined in the discussion of well GT-2.

Stable-isotope data are unavailable for water in 

San Antonio Creek near the Fenton Hill site or for 

perched ground water beneath the Jemez Plateau. 

Reasonable estimates for San Antonio Creek can be 

based on analyses for the creek in its upper reaches in 

Valle Toledo and for San Antonio Hot Spring, which 

flows into the creek: -90.0 to -93.0 per mil for 

deuterium and -12.65 to -12.85 per mil for 18O. Isotope 

values for perched water that infiltrates from the 

plateau surface can be estimated from a plot by Vuataz 

and Goff (1986, fig. 5); for the altitude of the Fenton 

Hill site they are -85.0 per mil for deuterium and -12.1 

per mil for I8O. The addition of a dilute water of such 

isotopic character to any of the reservoir fluids would 

shift the point for the reservoir fluid down and to the 

left in the plot in figure 36. Of the samples shown, only 

water from VC-2A could mix with the inferred dilute 

water to yield a combination like that in GT-2.

Once likely geothermal and dilute parent water 

has been identified, the result of its hypothetical mixing 

can be calculated with a simple balance equation 

(Trainer, 1975, p. 215):

(volgt x concgt) + (voldji x concdii) = 

(volgt + voldil) (concmix) (5)

where xgt volume of geothermal fluid; 

conCgt = concentration of a selected

constituent in the geothermal

fluid;

voldji = volume of the diluting fluid; 

concentration of the same

selected constituent in the

diluting water; and 

concentration of the same

selected constituent in the

mixed (resultant) water.

concdii =

conemix

72
PC-1

102- 

193- 

ILU

LL 1,007

Z

DEPTH,

2,009 

2,147

2,178

0

106

322 

394

LU 

LU 

LL

Z

I

Sj 1.131 

Q

1 Q'jn

PC-2

r\i_i.uviuivi

BANDELIERTUFF 

ABIQUIUTUFF

 PC 1-7

 PC 1-8

ABO FORMATION

 PC 1-9

 PC 1-10 £

LL 

 PC1-11 -

I

MADERA IT- LIMESTONE ft

Q

 PC 1-1

 PC 1-2 PC 1-4 

 PC 1-3 SANDIA 

 PC 1-5 FORMATION

GNEISS

BANDELIERTUFF 

PALIZA CANYON FORMATION

ABIQUIUTUFF

or* o H

n^ n n

ABO FORMATION LU

Z

I

nr* n n n

Q

^ PC 2-6

"MADERA LIMESTONE 

"~^-. PC 2-4

PC 2-5

 PC 2-7

u

200 ,

400

600

800

LU 

LL 1 ,000

z

jE 1 ,200

LU

° 1,400

1,600

1,800

2 000

)N

2,200

0

VTION 

200

400

600

{D 800

LU 

LL

-. 1 ,000

g 1,200

1,400 

1,600 

1,800 

2.000

r 5.2mg/L PC 1-7

L 5.3mg/L PC 1-8

-

 5.0mg/L PC 1-9

r

: (26) PC 1-10

> (58) PC 1-11

r

-

: PC 1-1

: * (0.9)

PC 1-2* , 

(0.7) PC 1-4 P.C. 1;.3 .PC 1-5" 

(0.6) (°-4 > (0-1)

3 500 1,000 1,500 2,000 2,500 3

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER (MG/L)

;

: 3.3mg/L PC 2-1 

-_ »3.9mg/L PC 2-2

~

7

r PC 2-3 ~ 

: (45)

'-

PC 2-4 PC 2-6 

(81) (5J)

PC 2-5

(76) PC*2-7 

(64)

000

10 20 30 40 50 60 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER (MG/L)

70

EXPLANATION 

PC 2-7 APPROXIMATE DEPTH WHERE SAMPLE WAS COLLECTED

 (64) CALCULATED VOLUME OF DILUTE WATER THAT, WHEN MIXED 

WITH ONE VOLUME OF RESERVOIR FLUID, YIELDS WATER 

LIKE THAT IN WELL VC-2A--Calculation based on chloride 

analysis

Figure 37.-Concentration of chloride in samples from water-yielding zones penetrated by wells PC-1 

and PC-2 (datafrom Shevenell and others, 1987, tables B-l and B-ll,and 1988, p. 36-40) 

Well locations shown in figure 5.

73
If the dilute water has concentrations of constituents 

near zero and if a unit volume of geothermal fluid is 

assumed, the equation simplifies to:

= concmix + (voldil x concmix), or

voldil =

concgt - conemix (6)

conemix

Use of this equation assumes that indicator-constituent 

ratios are preserved during dilution and mixing. 

Calculation of mixing volumes using analytical data 

for wells GT-2 and VC-2A (GT-2, 25 mg/L Li and 25 

mg/L B; VC-2A, 26.5 mg/L Li and 25.6 mg/L B, table 

6) results in estimates of 0.06 unit volume dilute water 

(using Li) and 0.02 unit volume dilute water using B for 

a unit volume of fluid from well VC-2A.

Isotopic analyses for wells VC-2A and WC 23-4 

were used with assumed values for water in San 

Antonio Creek near the Fenton Hill site to calculate 

shifts along dilution lines produced by mixing the 

reservoir fluids with small volumes of dilute water

(fig. 38). Well VC-2A yields the better fit, and 

agreement with the chemistry-based calculation of 

mixing volumes is fairly good. Taken together these 

independent arguments indicate that well GT-2 water is 

nearly as concentrated as its reservoir parent and that 

the parent water resembles VC-2A but is somewhat 

more mineralized and depleted in deuterium.

Mixing volumes calculated for samples from 

wells PC-1 and PC-2 (fig. 37) range from very large 

dilute contributions in perched water zones higher in 

the sedimentary section to mixtures in the basal 

limestone (PC-1) that approach the component ratio 

calculated for GT-2 water. The part of the Jemez 

Plateau that includes wells GT-2 and PC-1 is small and 

the regional significance of these two occurrences of 

mineral water cannot be estimated. It is of interest, 

however, that both wells that completely penetrate the 

sedimentary section in the plateau, where stratigraphic 

control of ground-water flow patterns may be greater 

than structural control, penetrated mineral-water 

conduits.

-70

-72

-74

-76

-78

-80

E -86

LLJ

-90

LU

Q -92

-94

-96

-98

-100

DILUTION WATER:

-90 PER MIL DEUTERIUM

-12.65 PER MIL OXYGEN-18

WC23-4

VC-2B -

SAN ANTONIO CREEK 

(assumed)

-13 -12 -11 -10 -9

DELTA OXYGEN-18 (<5 18 0), IN PER MIL

Figure 38.-Effect on stable-isotope composition of geothermal-reservoir fluid from addition of 

small volumes of a hypothetical dilute water to one volume of reservoir water (data 

from Trainer, 1978, table 8C; and Goff and others, 1988, table 1). Well locations 

shown in figure 5.

74
Well VC-1

The chemical and stable-isotope approaches 

applied to well GT-2 water were used to estimate the 

dilution ratio for mineral water in well VC-1 and to 

consider hypothetical parent reservoir water. The 

reservoir samples used in the calculations represent the 

six wells in the Redondo Creek field for which isotopic 

and extensive chemical data are available (Baca wells 

4, 13, 15, 19, 20, and 24). Six sets of chemistry-based 

estimates were made, each using three indicator 

constituents in water from well VC-1 and from one 

reservoir (Baca) well. Agreement of values is 

reasonable within each set. Similar estimates based on 

isotopic data also are internally consistent but different 

from those based on chemistry. The isotopic approach 

is useful in reinforcing the conclusion drawn by Vuataz 

and Goff (1986, p. 1847) that no single reservoir fluid 

and no single dilute fluid are parents of all derivative 

water outside the caldera.

Chemical and isotopic analyses are available for 

two water-yielding zones in well VC-1, at 1,585 and 

1,760 ft below land surface and both within Madera 

Limestone (table 13) (Goff and others, 1988, table 2). 

The waters are very similar; the following discussion is 

based on water from the upper zone. Mixing volumes 

calculated from concentrations of Li, B, and Cl in VC-1 

water are listed and summarized in table 14. These 

estimates range from 0.5 to 1.8 volumes of dilute water 

per unit volume of reservoir fluid. Isotopic data were 

used to calculate the dilution required to produce a 

given shift in isotopic composition along the dilution 

trend line from the isotopic composition in a 

geothermal well to that at a hypothetical source of 

dilute water (fig. 39). The estimates are similar to but 

somewhat larger than those from the indicator 

constituents, which range from 1 to 2.2 volumes of 

dilute water.

Table 13. Chemical and stable-isotope data for well VC-1

[Well location shown in figure 5. Ionic concentrations in milligrams per liter; isotope compositions in 

per mil (°/00) notation. Data from Truesdell and Janik (1986, tables 1, 3), White (1986, tables 1, 3),

and Goff and others (1988, table 2)]

8D 818O

Well depth Ca Mg Na K Li HCO3 SO4 Cl F B

VC-1 at 1,585 

feet below 

land surface

VC-1 at 1,760 

feet below 

land surface

49 17.8 883 85 8.00 942 56.8 964 3.94 8.55 -88.0 -11.35

47.8 11.9 804 84 7.27 919 74 853 4.74 10.1 5.3 -11.33

75
Table 14. Calculated volume of dilute water that, when mixed with a unit volume 

geothermal fluid, yields water similar to that in well VC-1 *

[Well locations shown in figure 5. Ionic concentrations in milligrams per liter; isotope compositions in pe

Data from Truesdell and Janik (1986, tables 1, 3), White (1986, tables 1, 3), and Goff and others (1

Stable isotopes Concentrations of indicator ions

Li

Well

Baca4

Baca 13

Baca 15

Baca 19

Baca 20

Baca 24

Number of 

samples

3

4

2

1

2

3

Average (°/00)

8D

-87.2

-88.0

-83.9

-83.1

-89.0

-83.0

8180

-10.05

-10.03

-8.54

-8.41

-8.15

-8.81

Number of 

samples

3

3

3

1

3

5

Average

15.0

17.7

16.3

21.0

13.0

19.6

B

Number of 

samples

5

6

7

1

3

5

Average

15.0

15.8

13.1

23.0

15.0

20.2

Cl

Number of 

samples

6

7

7

1

3

5

Averag

1,882

1,910

1,660

2,665

1,644

2,351

1 At 1,585 feet below land surface. Dilute water assumed to be from San Antonio Creek in southern part of caldera moat 

(negligible ionic concentrations; stable-isotope composition assumed as 8D-90.0 °/00 8 18O-12.65 °/00
5 -i

2 I

Inset

-90/ '-13

Baca4 and Baca 13, 

dilute 1: geothermal 

(Baca 13also 1:1)

-12 -11 

DELTA OXYGEN-18 (a"0), IN PER MIL

-80

-90

-95

-13 -12

Baca 24 

/ "Baca19 

Baca 15

Baca 20

-10

DELTA OXYGEN-18 (<5"O), IN PER MIL

Figure 39.- Formation of mineral water similar to that in well VC-1 (at 1,585 feet below land surface calculated from stable-isotope data for inferred dilute water and geothermal-reservoir fluid(data from Truesdell and Janik, 1986, table 3; and White, 1986, table 3). Lower 

plot shows hypothetical trend lines for progressive dilution; trend lines for other wells 

omitted for clarity. Upper plot shows examples of dilution ratios on four trend lines. 

Well locations shown in figure 5.

As was noted earlier, the three-dimensional 

complexity of Redondo Creek reservoir rocks and the 

wide range in character of its geothermal water became 

evident in the early 1980's when the release of 

proprietary data and extensive flow testing of several 

Baca wells provided geologic, hydrochemical, 

isotopic, temperature, and hydraulic data. Reservoir 

rocks beneath the Redondo dome were found to be 

highly compartmented by faults and stratigraphy 

(Nielson and Hulen, 1984). Scarcity of interference 

effects among wells during production tests suggests 

that many pairs of adjacent compartments are poorly 

interconnected hydraulically. Considerable variability 

in geothermal fluid was present from well to well. 

Several investigators (Smith and Kennedy, 1985; 

Truesdell and Janik, 1986, p. 1829-1832; and White, 

1986, p. 1864) recognized the presence of two distinct 

waters; Goff and others (1988, p. 6046) recognized 

three if the Sulphur Creek reservoir is included. 

Differences among several interpretations have not 

been resolved, but in the Redondo Creek reservoir the

fluids in Baca wells 4 and 13 differ substantially from 

those in Baca wells 15,19, and 24 (Truesdell and Janik, 

1986, p. 1829). Among numerous differences, fluid in 

Baca wells 4 and 13 is light isotopically and has lower 

salinity, higher temperature, and larger concentrations 

of CO2 and He; fluid in Baca 15, 19, and 24 is heavier 

isotopically and has higher salinity, lower temperature, 

and smaller concentrations of CC>2 and He. 

Concentrations of such conservative trace constituents 

as Li and B vary from one well to another, in much the 

same way as Cl concentrations. (See tables 4,6, and 12 

for examples of data and fig. 5 for areal distribution of 

the wells.)

Several of these differences are reflected in the 

estimates of mixing volume (table 14) and in the 

isotopic compositions shown in figure 39. If the two 

sets of mixing estimates and the areal distribution of 

isotopic composition are considered together, samples 

from Baca wells 4, 13, and perhaps 15 are the most 

likely representatives of parent fluids for water in well 

VC-1. Baca wells 4 and 13 best agree with the mixing

77
estimates but are not adequate in themselves; one or 

both together would require the addition of water more 

enriched in deuterium. If the choice is limited to the 

Baca wells because of their proximity to well VC-1 

(Goffand others, 1988, p. 6049) and both the mixing 

estimates and geographic distribution of the wells are 

considered (fig. 5), the situation shown in figure 39 is 

best explained by a parent water similar to some 

combination of waters from Baca wells 4 and (or) 13 

and from 15 and (or) 24.

For purposes of computation, any water that 

contains small concentrations of the indicator 

constituents can be selected for a hypothetical dilute 

water. The difficulty in selection of a dilute water for 

the mixing calculation, however, is two-fold and arises 

from the regional geohydrology. First, the dilute 

mixing member must be available perennially at a flow 

rate adequate to sustain the continuing flow of 

derivative water. Second, the only credible source for 

dilute parent water is perched ground water because the 

parent reservoir fluid comes from the principal or 

regional aquifer, far below the surface near the rim of 

the caldera. However, most bodies of perched water in 

this region are known to have small rates of yield and 

limited amounts of water in storage. Adequate yield 

supports the hypothetical stream-related aquifer as 

discussed for wells GT-2 and VC-1. A second credible 

source of dilute water for well VC-1 is ground water in 

the near-surface rhyolite, perched above the Abo 

Formation. As noted earlier, a number of warm springs 

in and near the ring-fracture zone yield dilute water. 

The largest are San Antonio Hot Springs (PI2), Spence 

Springs (H42), and McCauley Spring (H39), the latter 

two of which are near well VC-1 (fig. 5). One of these 

flow systems, or another similar to them, is a more 

credible source of dilute water for well VC-1 fluid; they 

all have adequate perennial flow, and their isotopic 

composition is in the range that explains the VC-1 

fluid.

Although a caldera source is well established for 

many principal constituents in the mineral water in 

Jemez Plateau and in and near Canon de San Diego, 

there is as yet no compelling evidence to show 

precisely how and where geothermal fluid escapes 

from the caldera. Discussion in an earlier paragraph 

favors movement of fluid from the Sulphur Creek 

subsystem into the sedimentary section beneath the 

Jemez Plateau near wells GT-2 and PC-1. The further 

course of that fluid has not been established, but the 

possibility of southeastward flow beneath the plateau, 

to Canon de San Diego, needs examination. Nearer the 

Jemez Fault Zone, electrical resistivity soundings

(Jiracek, 1974,1975; Jiracek and others, 1975) suggest 

a gap in the ring-fracture intrusives near the site where 

San Antonio Creek flows out of the caldera. The 

proximity of this site to the fault zone, which extends 

along Canon de San Diego and presumably influenced 

its formation, provides a logical general explanation for 

escape of reservoir fluid downcanyon in the subsurface. 

This hypothesis is consistent with the conceptual 

model of flow from the caldera and through the Jemez 

Fault Zone developed by Goffand others (1992, p. 

193). As noted earlier, fumaroles and associated 

hydrologic phenomena in Canon de San Diego outside 

the rim of the caldera near Battleship Rock indicate 

geothermal-fluid conduits at depth. Synthesis of 

thermal data for deep wells in the Jemez Plateau-Canon 

de San Diego area (Goffand others, 1988, p. 6043) 

suggests that as much as half the subsurface discharge 

from the caldera may flow along the Jemez Fault Zone.

Jemez Springs and Soda Dam

Earlier discussion noted both significant 

similarities and differences between the mineral water 

at Jemez Springs and at Soda Dam. Despite 

geochemical signatures indicating that both are 

derivatives of geothermal-reservoir fluids and the 

geographic proximity of the springs, the water differs 

significantly. The water at Jemez Springs is hotter but 

carries a much smaller dissolved-solids load, although 

its content of SO4 is out of proportion to the rest of its 

mineral content. The two groups of springs may drain 

different conduit systems, which are isolated from one 

another and differ in size and shape. Further, the 

differences between the two groups of springs may be 

related to two aspects of mixing the nature of the 

dilute water and the location of the mixing site.

Potential sources of dilute water for the mixing 

process have not been examined critically in published 

discussions of the mineral water. Local ground water 

along the route of escape of geothermal fluid into and 

through the rocks outside the caldera has been assumed 

to provide an adequate source of the dilute water. In 

discussions of wells GT-2 and VC-1, the dilute water 

was assumed to be ground water that had infiltrated 

from streams in the moat or from perched aquifers 

above conduits for the escaping geothermal fluid. This 

assumption was based in part on proximity and in part 

on the realization that there may be few places, except 

near infiltrating streams and the few known extensive 

perched aquifers, where dilute ground water is 

available in the quantities needed (approximately 50-

78
100 gal/min). This conclusion is discussed in the next 

section of this report.

A source beneath the moat within the caldera is 

thought to be a likely dilute mixing member for Jemez 

Springs water. It offers not only a supply of adequate 

volume and rate of flow but one of moderately high 

temperature (100-150 °C; see Goffand others, 1986, 

fig. 5). Direct covariation of 864 and Cl in the Jemez 

Springs water (fig. 34D) implies that little S04 is added 

to the water after the last major stage of mixing; hence, 

the dilute water (1) brought most of its S04 load to the 

site of that last mixing or (2) gained it there. Part of the 

SO4 load in a mixed water is inherited from the parent 

geothermal fluid, and part may have been generated 

from H2S along the flow path. A third potential source 

of SC>4 is Sulphur Creek, which drains the Sulphur 

Springs area and joins San Antonio Creek upstream 

from where the creek flows out of the caldera (fig. 6). 

Sulphur Creek carries away much of the mineral matter 

emitted by the springs; one sample from Sulphur Creek 

at its mouth contained 200 mg/L SO4 (Trainer, 1978, 

table 6). Part of the dissolved load in Sulphur Creek is 

diverted to and stored in the local ground-water 

reservoir in alluvium within the moat, and if groundwater storage in that reservoir is sufficiently large it 

may provide a substantial source of water (containing 

the requisite dissolved SO4) for the dilution of escaping 

geothermal fluid. No data are available to test this 

hypothesis.

Two factors could contribute to the effective 

maintenance of temperature over a flow distance of 

several miles (presumably a distance similar to that in 

which Soda Dam water has lost much more heat). 

Contributing water could have high temperatures at the 

site of mixing, and flow conduits to Jemez Springs 

could be of a type that minimizes heat loss during 

transport.

Water like that in the well VC-1 sample meets 

the requirements for the less mineralized mixing water 

in the last-stage dilution of Soda Dam water: Soda Dam 

and VC-1 waters are similar in terms of their strontium 

isotopes (Vuataz and others, 1988, table 2); they are 

also of similar composition, but the Soda Dam water 

has larger constituent concentrations. Additionally, if 

the last stage(s) of mixing to form Soda Dam water 

occurred in Canon de San Diego, the loss of heat 

indicated at Soda Dam is largely explained by the 

moderate to low temperature of the "dilute" member(s) 

(approximately 100 °C near the caldera rim, less than 

50 °C farther downcanyon).

Trainer (1984) inferred from the large total 

volumes of limestone removed from the conduit

systems that the conduits are likely larger and more 

conductive than required for transport of the modest 

quantities of water now discharged by the springs. 

From this argument and from inference of rapid 

pressure transmission and slow mass transport in the 

conduits, Trainer (1984) concluded that the conduit 

systems contain large quantities of confined water in 

transient storage, with fluctuations in discharge 

governed by fluctuations in prevailing head.

GROUND-WATER SYSTEM

Principal Aquifers

Several lines of evidence noted in earlier sections 

reveal the presence of diverse ground water and 

aquifers in this region. At least two principal or 

regional aquifers are within the southwestern Jemez 

Mountains: one is the rift-fill sediments at the southern 

edge of the study area and the other is the geothermal 

reservoir(s) in Valles Caldera and their outflow 

conduits. There are at least three types of perched 

bodies of ground water: (1) those, commonly in 

volcanic rocks, that overlie the relatively impermeable 

Abo Formation; (2) those in permeable sedimentary 

strata that overlie less permeable beds within the 

sedimentary section, as in wells PC-1 and PC-2 or in 

Canon de San Diego near the caldera rim; and (3) those 

in small, disconnected bodies of material that overlie 

less permeable rocks, as in parts of the ring-fracture 

moat within the caldera or in alluvial deposits that are 

in hydraulic connection with the Jemez River along 

part of its course. The third type is small and not of 

regional importance. Consequently, this is not 

discussed further in the report.

The geohydrologic nature of the rift-fill 

sediments at the southern edge of the study area, 

between San Ysidro and Bernalillo (fig. 1), is not well 

known. However, it is presumed to be similar to that in 

the explored part of the Albuquerque Basin, where 

thickness is measured in thousands of feet and 

hydrologic properties are governed by the sedimentary 

and stratigraphic nature and structure of the deposits.

The hot-water system beneath the central and 

western areas of the Valles Caldera is considered the 

principal or regional aquifer in the caldera because it 

extends to depths of at least several thousand feet and 

perhaps as far as the rock has continuous openings that 

permit flow. (All other ground water recognized in the 

caldera is perched at higher levels.) South and

79
southwest of the caldera rim, mineral-water conduits 

near the base of the sedimentary section, above the 

relatively impermeable crystalline rocks, are the 

downgradient extension of this principal aquifer 

beneath Canon de San Diego and the Jemez Plateau. In 

this form the principal aquifer extends southward as far 

as Jemez Pueblo. Near there it merges with the regional 

aquifer in fill deposits of the Rio Grande Rift. No data 

exist on the regional aquifer farther west, but the 

aquifer in the east slope of the Nacimiento Mountains 

west and southwest of the caldera and west of Jemez 

Pueblo likely merges to the east with the Jemez 

Plateau-Caflon de San Diego extension of the caldera 

aquifer. The mixed-water merger zone presumably lies 

beneath the basins of the Rio Cebolla and Rio 

Guadalupe to the north and beneath Jemez Pueblo and 

Zia Pueblo lands to the south where rocks of the 

Nacimiento Mountains abut rift-fill deposits in the 

border fault zone of the rift.

Chemical differences among the known 

discharge fluids from Valles Caldera indicate outflow at 

several places in the ring-fracture zone. All sites of 

discharge appear to be in the western and southwestern 

parts of the caldera rim. No evidence of escaping 

geothermal fluid has been found on the northwest or 

north flanks of the Jemez Mountains. The stableisotope composition of ground water rules out leakage 

to the east (Fraser Goff, Los Alamos National 

Laboratory, written commun., November 1993).

Evidence is sparse regarding the general 

directions of flow within the southern part of the 

caldera reservoir(s) and the locations of breaches in the 

ring-fracture zone through which geothermal fluid 

escapes. As noted in an earlier discussion, Grant and 

others (1984) suggested that geothermal fluid flows 

from the Sulphur Springs reservoir toward Redondo 

Creek and then southward beneath Canon de San 

Diego. Goff and others (1988) inferred, on the basis of 

proximity, that fluid escapes from the Sulphur Springs 

reservoir by flowing southwestward beneath the Jemez 

Plateau. The isotopic similarity of the Sulphur Springs 

geothermal fluid and the water at Soda Dam, noted 

earlier, supports Grant's interpretation. Chemical and 

stable-isotope data cited in this report in the discussion 

of well GT-2, however, may substantiate the inference 

of flow beneath the Jemez Plateau. Further support is 

provided by a report of H2S in the plateau region about 

2 mi west of the Fenton Hill site (fig. 10) (Bailey, 1961; 

R.A. Bailey, U.S. Geological Survey, oral commun., 

1974), which suggests the presence of boiling fluid in 

the subsurface. Hence, parts of the flow from the

Sulphur Springs reservoir likely follow both major flow 

paths down Caflon de San Diego and beneath the 

Jemez Plateau (fig. 1).

Canon de San Diego San Ysidro Area

Consideration of the general course of fluid 

escape from the caldera and its flow down Canon de 

San Diego is facilitated by comparing geologic 

sections in figures 11 and 40. The schematics show the 

enormous disparity between the depth of the caldera 

reservoir(s) and the thickness of the section of 

sedimentary rocks outside the caldera, in which the 

derivative mineral water flows away. As earlier noted, 

Grant and others (1984) placed the nominal 

potentiometric surface for the Redondo Creek reservoir 

at an altitude of about 7,875 ft, or about 2,000 ft above 

the level of the basal limestone just outside the ringfracture zone. In the vertical section (fig. 11) artesian 

flow in the reservoir near the ring-fracture zone moves 

laterally and upward by convection in a direction 

perpendicular to the lines of equal temperature. The 

rising reservoir fluid escapes chiefly through the lowest 

openings found by the fluid in the basal limestone. 

Head loss, which must occur between the reservoir and 

the ring-fracture zone, is thought to be great enough to 

permit dilute water in the alluvial aquifer within the 

moat to infiltrate and mix with the escaping reservoir 

fluid. The near-surface water table is at an altitude of 

about 7,610 ft where San Antonio Creek flows out of 

the caldera and at an altitude of about 7,800 ft near the 

Fenton Hill site.

Efforts to identify and characterize flow conduits 

outside the caldera wall have met with only limited 

success. The conduits seem to have developed 

preferentially in the basal part of the limestone section 

regardless of whether their primary geologic control is 

stratigraphic (as in the Jemez Plateau, well PC-1) or 

structural (well VC-1 and springs at Soda Dam). 

Wherever the hydraulic situation at mineral springs is 

evident (Soda Dam, Jemez Springs, springs D6 and 

All; figs. 26 and 41), the springs are seen to be artesian 

(confined) features. Earlier discussion argues that 

mineral water, in part derived from the caldera 

reservoir, flows southward beneath Canon de San 

Diego at least as far as Jemez Pueblo, about 20 miles in 

straight-line distance. Flow over such distances, 

although preserving the chemical character of the fluid, 

is not unusual in mountainous terrain, according to 

Ingebritsen and Sorey (1985, p. 853-855). Where 

pathways for lateral flow of liquid water exist, phase

80
Resurgent 

dome

Soda Dam 

Springs

xxxxxxxxxxxxxxxx

xxxxxxxxxxxx 

xxxxxxxxxxxxx

MOATRHYOLITES

CALDERA FILL (Bandolier 

Tuff and other rocks)

EXPLANATION 

TUFF (Bandelier Tuff)

SANDSTONE, SHALE 

(Abo Formation)

LIMESTONE (Madera and 

Sandia Formations)

CRYSTALLINE ROCK

GROUND-WATER FLOW 

(geotnermal) ?

FAULT

Figure 40.-Flow paths of reservoir fluid escaping from Valles Caldera. The springs at Soda 

Dam and Jemez Springs drain different conduit systems. Well location shown 

in figure 5.

separation occurs in a zone of two-phase flow, with 

liquid water tending to move laterally and steam 

tending to rise. Sparse evidence suggests the presence 

of at least two distinct flow systems: one that may be 

beneath the canyon proper and one that branches off to 

the west, near Soda Dam, and trends through faulted 

terrain to the vicinity of Jemez Pueblo. Water in the two 

systems mixes near San Ysidro with mineral water 

from the Nacimiento Mountains and with freshwater 

from rift-fill deposits. From here the mixed water, 

bearing a considerable load of dissolved salts, flows 

eastward and southeastward into the principal aquifer 

in the Albuquerque Basin.

The mineral water from Canon de San Diego that 

mixes with other water near San Ysidro is itself a 

mixed water (or series of mixed water). This 

interpretation, based on the variation of water 

chemistry at the springs with time, depends on the 

confined nature of the conduit systems. An earlier 

section of this report (fig. 33) ascribed the small Cl 

concentrations to (1) increases in ground-water

recharge and in the rate of mixing of reservoir fluid and 

(2) the presence of more dilute local ground water 

during the annual snowmelt flood event. Also 

explained was the timing of small Cl concentrations at 

the springs (some months distant from the annual 

flood) in terms of lag time required for mass transport 

from mixing site to spring. In contrast to Cl 

concentration, water discharge and Cl loads of the 

springs are largest during the annual snowmelt flood 

event (fig. 42). These peaks, displaying virtually no lag 

time, are attributed to the rapid transmission of head 

change from the site of mixing to the discharge point by 

pressure waves in confined conduits, with increased 

spring flow supported by water in the conduit system 

near the springs. Trainer (1984, p. 252-253) considered 

three explanations for these pressure waves: (1) 

changes of head in the geothermal reservoir, (2) 

repetitive external loading and unloading of conduits 

by flood water at land surface, and (3) fluctuations in 

head within conduits transmitted by the dilute water at 

sites of mixing.

81
(A) NORTH 

6,400

SOUTH

LLJ 01

UJ > 6,200

6,000 01 m

0 W

§ 01 5,800

5 m 5,600

5,400

!ir----nSpda Dam ' ' ' '

Jembz'-----.-.._ """""" -----._ D6 

- Springs ""----..__ """" ---«^.__

A10

2 

106°50'

6 8 

DISTANCE, IN MILES

10 12

106°30

(B)

35° 

40'

35° 

20'

,_I v\Los A'amos 

Rim of ^ ^V^

D Pena 

Blanca

ox. D Santp 

o$ f Domingo 

^ J Pueblo

] San Felipe 

Pueblo

Algodones

R. 1 W. R.1 E. R.6E.

10 MILES

16

T. 

18 

N.

17

16

15

14

T. 

13 

N.

10 KILOMETERS

EXPLANATION

AREA OF EXPOSED 5400- 

QUATERNARY-TERTIARY 

RIFT-FILL DEPOSITS (from 

Smith and others, 1970)

FAULT-Dashed where @ 

approximate (from Smith 

and others, 1970)

GENERALIZED DIRECTION OF

GROUND-WATER MOVEMENT C3 

(from Craigg, 1992, fig. 18)

APPROXIMATE WATER-TABLE 

CONTOUR-Contour interval 

100 feet. Datum is sea level 

(from Craigg, 1992, fig. 18)

STREAMFLOW MEASUREMENT 

SITE (from Craigg. 1992)

SPRING 

WELL

Figure 41 .--(A) Inferred profiles of piezometric surfaces in Canon de San Diego and (B) approximate 

water-table contours and generalized direction of ground-water movement in rift-fill 

deposits. 82
3°2o

140

120

100

80

60

40

20

I I I I I I I I I I f

JEMEZ RIVER BELOW 

SODA DAM (site 1)

1 I I I I I I |

JEMEZ RIVER BELOW 

'JEMEZ SPRINGS (site 2)

> / - .

, JEMEZ RIVER BELOW EAST FORK, NEAR JEMEZ SPRINGS 

(08321500) , "I

/ \ ' M 

/ v-' \/

I ' I I

JAN JUNE 

1973

DEC JAN JUNE SEPT

1974

Figure 42.-Chloride load at three sites on the Jemez River, 1973-74 (from Trainer, 1984, fig. 6). 

Locations shown in figure 6.

The explanation of pressure waves due to head 

changes in the geothermal reservoir appears untenable 

because the synchronism shown in the hydrographs 

would require nearly instantaneous recharging of the 

geothermal reservoir. Tritium data show that the 

reservoir fluid is at least 60 years old (Vuataz and Goff, 

1986, p. 1851).

Repetitive external loading and unloading of 

conduits by flood water on land surface nearby can 

form near-synchronous pressure waves in confined 

aquifers. However, the magnitude of such loading is 

unlikely to be more than a few feet of water on the 

streambed, many hundreds of feet above the subsurface 

conduit. Additionally, this mechanism provides no 

explanation for the small concentration of Cl detected 

some time afterward at the springs.

In contrast, a pulse of recharge to a flowing body 

of mineralized water by more dilute ground water from 

an overlying aquifer during the snowmelt event can 

provide the short-term head fluctuation and the 

(delayed) change in ionic concentration that is

observed downgradient at the springs. The near 

coincidence of peaks in streamflow and spring flow is 

believed to be a transient pressure effect caused by 

pulses of recharge to confined conduits. Fluctuations in 

water chemistry described earlier are transport 

phenomena that lag far behind transient pressure 

changes.

Study of the caldera-derived mixed water in the 

region outside the caldera is hindered by a scarcity of 

data sites, limited to a few wells and springs. The 

sparseness of data is especially significant in estimating 

the quantity of reservoir-fluid solutes that escape from 

the caldera and flow into the major aquifer in the 

Albuquerque Basin in the Rio Grande Rift.

Earlier discussions describing figure 35 noted a 

few aberrant values in samples from Soda Dam and 

Jemez Springs that could imply further dilution. At 

Soda Dam the pertinent data are for Hidden Spring, in 

the flood plain a short distance upstream from the dam 

(table 12). Tritium data for Hidden Spring and for the 

Jemez River above Soda Dam (table 12) strongly

83
suggest dilution of the mineral water by the river, more 

evidence of local dilution at Jemez Springs. Stableisotope and Cl data for Hidden Spring and the Jemez 

River are consistent with local dilution. Concentrations 

of Cl in the river during 1982-83 are large because of 

the dissolved load in streams upstream from Soda 

Dam. These Cl concentrations are thought to reflect the 

escape of ponded effluent stored during production 

testing of geothermal wells in 1981 and 1982.

At Jemez Springs the location of major springs 

along fault zones, the consistency of chemical 

composition of the water, and the levels of dissolvedconstituent concentrations in the spring water indicate 

that the water probably flows through discrete conduits 

in the alluvium that overlies the bedrock. Nonetheless, 

part of the flow up through the alluvium is known to be 

porous-media flow, and the spatial pattern of water 

chemistry is complex. Isotopic plots for Jemez Springs 

samples suggest local dilution (fig. 35). Head in the 

mineral-water conduits is higher than river level, so 

mixing must occur through escape of mineral water 

into the enclosing body of dilute water.

Evidence of mineral water from Valles Caldera is 

less clear in Caflon de San Diego downstream from 

Jemez Springs than in the areas already described. 

Chemical data, however, strongly imply that 

subsurface mineral water flows as far south as Jemez 

Pueblo, where it is one of four different types of ground 

water that merge: (1) Jemez mineral water rises 

through the alluvium from the underlying bedrock and 

mixes with (2) ground water in the alluvial deposits and 

(3) mineral water from the southern Nacimiento 

Mountains, and all these types of water mix with (4) 

water in the rift-fill deposits. This water moves 

southeastward to the major aquifer in the Albuquerque 

Basin.

The locations of five springs (D6, A8, A9, A10, 

and Al 1) in or near the lower Canon de San Diego that 

are thought, on the basis of water chemistry, to be fed 

in part by Valles Caldera geothermal fluid are shown in 

figure 4IB. Chemical analyses of samples from these 

and several additional sites are listed in table 15; majorion composition of the samples is summarized in figure 

43.

A8 

Owl Spring (3)

RioGuadalupe

above Jemez River

(site 20)

A9 

Tunnel Spring

Jemez River above

RioGuadalupe

(site 15)

Jemez River

at Highway 4

near San Ysidro

(site 22)

Soda Dam springs (13)

Mineral springs 

near San Ysidro (7)

A6 

Swimming Pool Spring

C3

Kaseman oil-test well 

(Zia Hot Well) (13)

 Jemez Springs (9)

A11 

Indian Spring (4)

A10 

Salt Spring (2)

EXPLANATION 

 ^ SPRING

O SURFACE WATER-Site

numbers refer to figure 47

(4) NUMBER OF ANALYSES USED 

TO DEFINE DISTRIBUTION 

FIELD

d> GROUPS OF SPRINGS OR 

WELLS

D6

Spring near confluence 

of Jemez River and 

RioGuadalupe (2)

CHEMICAL CONSTITUENTS

SO4 + Cl Sulfate + chloride

Ca + Mg Calcium + magnesium

Na + K Sodium + potassium

CO, + HCO, Carbonate + bicarbonate

PERCENTAGE OF TOTAL IONS, IN MILLIEQUIVALENTS PER LITER

Figure 43.--Ranges in chemical composition of water from wells and springs in the lower 

Canon de San Diego, near San Ysidro. Well and spring locations shown 

in figure 41.

84
Table 15. Chemical and isotopic analyses of ground water in and near the lower Canon de 

[Ionic concentrations in milligrams per liter; stable isotopes in per mil (%o) notation; tritium (3H) in tri

Site 

number 

(see fig. 

41B) 

data1

JD6

1A8

3A9

1AIO

3A11

3C3

1C3

3A6

3A1

'Al

'AK?)

8A2

8A3

8A5

Sample 

number Date

VA-40 4-81

VA-38 3-81

5-24-73

VA-36 3-81

8-30-73

12-02-74

VA-53 4-80

9-14-24

3-14-64

VA-33 8-79

VA-130 5-83

12-20-74

12-20-74

12-20-74

Ca

36

73

100

89

110

340

321

260

157

375

305

300

390

220

Mg

5.2

10.4

15

26.4

21

62

61

70

70

128

71.3

68

65

110

Na

161

34

120

1,950

1,300

3,300

3,440

62,400

1,760

1,710

1,720

2,000

3,000

3,800

K

7.6

2.1

7.3

94

73

80

77

-

71

75.3

77

81

91

140

HC03

367

311

416

1,870

1,456

1,086

1,068

1^01

1,080

1,860

1,740

2,005

1,855

2,260

C03

0

0

0

0

0

0

0

0

0

0

0

0

0

4

SO4

127

33S

702

270

2,690

3,430

1,728

1,220

1,165

1,183

1,200

2,600

3,700

Cl

71

27.8

96

2,380

1,200

3,180

3,210

2,330

1,680

1,820

1,671

1,900

2,400

2,700

F

9.3

1.4

3.0

10.8

4.0

2.8

4.51

-

2.9

3.95

3.32

3.4

4.0

2.0

Li

0.5

.18

7.4

6.7

7.2

6.0

~

6.4

5.3

8.1

6.1

5.2

6.3

Sample from Shevenell and others (1987, tables B-II, B-IV).

2Date of isotope sample is 8-79.

3Sample from Trainer (1978, tables 5, 8C).

4Date of isotope sample is 12-13-74.

5Date of tritium sample is 2-83.

6Sodium -i- potassium as sodium.

7Date of tritium sample is 5-16-73.

8Sample from Mariner and others (1977, tables 2,3,5).
Spring D6 flows from a fault zone within granite 

located on a hillside, about 320 ft above the level of the 

Jemez River at the base of the hill. Concentrations of 

Cl, Li, and B in the spring water (table 15) indicate that 

geothermal fluid is a likely component. At least three 

hypotheses can be considered for likely flow paths to 

spring D6: (1) flow through stratigraphically and (to the 

south) fault-controlled openings beneath the Jemez 

Plateau and the terrain west of Canon de San Diego; (2) 

flow through fault- or bedding-controlled openings at 

depth beneath Canon de San Diego; and (3) flow 

through fault-controlled conduits that leave Canon de 

San Diego near Soda Dam (see fig. 5) and trend 

southward through mountainous terrain west of Canon 

de San Diego. The first explanation is unlikely, despite 

the presence of mixed water beneath the plateau at 

wells GT-2 and PC-1, because water from spring D6 

lacks a limestone signature. Water-level data imply the 

presence of two confined flow systems in and near 

lower Canon de San Diego one beneath the canyon 

and one to the west, beyond the ridge that bounds the 

canyon. Thus, the second and third flow paths 

hypothesized may be valid. Regardless of path, spring 

D6 water is a credible mixture of mineral water and 

dilute ground water like that at Soda Dam or Jemez 

Springs. Calculations based on Cl, Li, and B indicate 

mixing proportions of approximately 26 (dilute water) 

to 1 (mineral water) for a parent water similar to that at 

Soda Dam and 16 to 1 for a parent water similar to that 

at Jemez Springs.

Owl Spring (A8) and Tunnel Spring (A9) flow 

from limestone in the hilly terrain west of Canon de 

San Diego. Concentrations of Cl, Li, and B in both 

(table 15) imply that the water is a mixture of mineral 

water and dilute ground water; each has a limestone 

signature (fig. 43). Both represent the upper of the two 

inferred flow systems (fig. 41 A).

Other spring water and water from well C3 have 

a wide range in concentration, though all are mineral 

water and many are warm. Salt Spring (A 10) flows 

from the Triassic Chinle Formation sandstone west of 

the river and within Canon de San Diego. Indian Spring 

(Al 1, fig. 41) is located in the bed of the Jemez River 

on Jemez Pueblo land; the spring water is thought to 

come from limestone underlying the alluvium. Springs 

Al, A2, A3, and A5 (fig. 4IB) represent a larger 

number of small mineral springs, cold or slightly 

warm, that flow from the Chinle Formation sandstone 

in the southern part of the Nacimiento Mountains west 

of San Ysidro. Spring A6 (Swimming Pool Spring) is

one of a number of springs that are clustered along the 

fault zone at the mountain front. Well C3 ("Warm 

Spring"), an abandoned oil-test well (Clark, 1929; 

Renick, 1931) at the west base of the Nacimiento 

Mountains, discharges thermal mineral water (about 50 

°C), at a rate of 80-100 gal/min, from the Madera 

Limestone. The mineral springs near San Ysidro 

appear to be fault controlled and well C3 is located near 

the fault zone. All the springs and well C3 in the 

Nacimiento Mountains have built extensive deposits of 

travertine.

Trainer (1974) concluded that the composition of 

mineral water in the lower Canon de San Diego and 

near San Ysidro indicates dilution from a single parent 

geothermal fluid from Valles Caldera. The water and 

features at the west foot of the Nacimiento Mountains 

(for example, spring A6 and well C3) appear to be 

associated with head relations different from those in 

the lower Canon de San Diego; thus, substantially 

different flow paths must be involved if their 

geothermal parent also is derived from Valles Caldera. 

More detailed studies (Vuataz and Goff, 1986; 

Shevenell and others, 1987) have since shown with 

stable isotopes and water chemistry that the 

Nacimiento Mountains water and those near San 

Ysidro are derived not from a Valles Caldera parent but 

from a separate low-temperature geothermal system 

along the Nacimiento Fault Zone. The Nacimiento 

Mountains water has come from or through limestone 

and gypsum-bearing rocks and, therefore, is 

characterized by high concentrations of HC03 , S04, 

Cl, Li, and B. Their most conspicuous differences from 

mineral water in the upper Canon de San Diego are 

larger concentrations of Cl and particularly of SO4 .

Many plots prepared in studies of chemical and 

isotopic data for springs in the Jemez Mountains 

(Vuataz and Goff, 1986, fig. 4; Shevenell and others, 

1987, figs. 8-14), including several in this report (for 

example, fig. 43), display extended linear data 

distributions that may be due to (1) temporal variation 

in chemical and isotopic character or (2) dilution or 

mixing of fluids. Mixing of water in the area near San 

Ysidro is highly probable because the general 

directions of ground-water flow from surrounding 

areas are toward San Ysidro from the San Juan Basin 

and the Nacimiento Mountains to the west and 

northwest; from the Jemez Mountains to the north; and 

from parts of the Rio Grande Rift to the north and 

northeast (figs. 3 and 4IB).

86
Figure 44 suggests two mixing systems: (1) The 

Valles Caldera-Canon de San Diego system, already 

discussed in this report. This system includes the 

caldera fluids, spring water at Soda Dam and Jemez 

Springs, and water in well VC-1. Water from springs 

A8, A9, and D6 are thought to be very dilute 

representatives of this system. (2) The Nacimiento 

Mountains-San Ysidro system whose concentrated 

end member is represented by well C3 and whose other 

end member is a mixture with Canon de San Diego 

water (for example, A10 and All). The mineral springs 

near San Ysidro (Al, A2, A3, and A5) represent a 

series of intermediate mixtures in the Nacimiento 

Mountains system. The stable-isotope plot in figure 45 

confirms the conclusions drawn from the chemistry.

Chemical and discharge data for the Jemez River 

contribute to further understanding of the mineralwater discharge at Jemez Pueblo. As noted earlier 

during the discussion of the Jemez River, the stream 

carries a substantial dissolved load downstream from 

Soda Dam, largely Ca, Mg, and HCC>3 from limestone 

and Na and Cl from the geothermal reservoir. Part of 

the water and its dissolved load continues downstream 

and out of the Jemez Mountains as streamflow; part 

infiltrates the alluvium beneath the stream and 

continues its flow as ground water. Water moves from 

the stream to the ground and from the ground to the 

stream repeatedly in a complex areal pattern in 

response to the water-yielding character of the 

alluvium (specific yield) and local variations in both 

stream stage and head in the underlying aquifer.

Craigg (1984, table 7; 1992, p. 74-76, figs. 24, 

25, and tables 3,4) investigated the relations between 

shallow ground water and the Jemez River along the 

24-mi reach between the USGS streamflow-gaging 

station Jemez River near Jemez Pueblo (08324000; 

station 1 in fig. 4IB) and Santa Ana Pueblo. Two sets 

of streamflow measurements were made, both at times 

of steady streamflow and small or negligible inflow 

from tributaries. Measurements on March 1, 1984, 

represent base-flow conditions with little 

evapotranspiration just before the annual snowmelt 

flood. Measurements on August 1,1984, represent latesummer low flow with strong evapotranspiration. 

Because the August study was complicated by 

withdrawals for irrigation, only the March data are 

examined here.

The March data for the river reach between the 

streamflow-gaging station (1) and the site near San 

Ysidro (6) (fig. 4IB) are summarized in table 16. 

Except for a losing reach between Vallecito Creek and 

Jemez Pueblo the river was a gaining stream, and the 

rate of gain generally increased downstream.

Moreover, the farthest downstream reach (between 

sites 5 and 6) had the greatest gain in Cl load. Thus, the 

reach between sites 1 and 2 showed an increase of 

about 1 cubic foot per second per mile (ft3/s/mi) 

(discharge) and about 1.3 grams per second per mile 

(g/s/mi) (Cl load). The corresponding rates in reach

4-5 were about 1.8 ft3/s/mi and 10.8 g/s/mi and in reach

5-6 were 1.9 tf/s/mi and 16 g/s/mi. Downstream from 

station 6, the Jemez River was gaining over most of the 

remainder of the measured reach; however, salts were 

not studied further because of salt contributed by the 

Rio Salado (Craigg, 1992). Springs A10 and A11 (table 

15 and fig. 4IB) are in reach 4-5, and a well near the 

Jemez River in reach 5-6 (not shown) yielded water 

similar to that from the springs (Craigg, 1992, p. 17). 

Inasmuch as uncontaminated (unmixed) ground water 

in the rift-fill deposits contains much smaller 

concentrations of Cl (Craigg, 1992, fig. 8), it is evident 

from these data that mineralized water is moving 

upward from the bedrock into the overlying alluvium 

and into the stream.

The earlier argument that high concentrations of 

S04 in ground water in upper Canon de San Diego are 

due in part to the oxidation of H2S that rises in flow 

conduits from boiling fluid at depth would not be 

tenable near San Ysidro and Jemez Pueblo, where the 

temperature of mineral water is far below the boiling 

point. Hence, the origin of SO4 in mineral water of 

Canon de San Diego is upcanyon; 864 in Nacimiento 

Mountains water is derived largely from gypsiferous 

rocks in the Nacimiento Mountain front and (or) the 

San Juan Basin. From this reasoning relations among 

the different mineral waters (figs. 43-45) possibly can 

be studied. The concentration of 804 in water can be 

expressed in terms of the ratio C1/SO4 (both in 

milligrams per liter). In 16 analyses of water from well 

C3 this ratio ranges from 0.78 to 1.18 and the mean is 

0.92. In nine samples from spring A6 (Swimming Pool 

Spring) and the mineral springs near San Ysidro (Al, 

A2, A3, and A5) the ratio ranges from 0.73 to 1.6 and 

the mean is 1.3. In five samples from springs A10 and 

Al 1 on Jemez Pueblo land in or near the Jemez River 

the range is 3.0 to 5.0 and the mean is 4.0. In 18 

samples collected at the Jemez River near Jemez 

(08324000) gaging station downstream from the 

confluence of the Jemez River and Rio Guadalupe the 

range is 0.5 to 17.4 and the mean is 3.8. These mean 

ratios suggest that fluid from Valles Caldera dominates 

the mineral water at Jemez Pueblo and that the 

principal region of mixing of Canon de San Diego and 

Nacimiento Mountains water is near and west of San 

Ysidro.

87
cc

UJ 1- 

_l

oc 30

UJ

0.

w

I 25

O

_j _j 

2 20

Z

 7TRATIOI en

w 10 

O

z

0

S 5

Z)

X

H

-J 0

I I I I I III

A VC-2B

_ _

 VC-2A

(" """I BACA 24

^- ^

£± BACA 14

SODA f\ cr=a,ArA , 

DAM Li BAUA 4 

SPRINGSfV

~ JEMEZ/O VC-1

SPRING9'4X' /^v.

\!/ A1 1 \. ^ ^^^ X* "\ C3

- v^ ' -_^y C! _ y

D6 MINERALSPRINGS

A8/ NEAR SAN YSIDRO

e!^ I I I I I I I I

1,000 2,000 3,000 4,000 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

30

< 25

20

O 15

Z 10

UJ

O 

Z 

O 

O 5h

z 

o

DC

§ 0

B

SODA

DAM

SPRINGS

VC-1

JEMEZ 

SPRINGS

D6

VC-2B _

'C-1 

\ A11

*$ n vi * .

BACA 24

BACA4

VC-2A

BACA 1 3

C3

A10

MINERALSPRINGS 

NEAR SAN YSIDRO

1,000 2,000 3,000 4,000 

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

Figure 44.-Covariation of (A) lithium and chloride and (B) boron and chloride in representative 

reservoir fluids in Valles Caldera and in mixed water in and near Canon de San 

Diego (data from Renick, 1931; Mariner and others, 1977, table 2; Trainer, 1978; 

White, 1986, table 1; Shevenell and others,1987; and Goff and others, 1992, 

tables 1 and 2). Well and spring locations shown in figures 5 and 41 B.

-70

-75

DC 

111 

Q_

Z

~ -80

-85 

-95

METEORIC-WATER LINE 

FOR JEMEZ MOUNTAINS

(VUATAZAND

GOFF, 1986)

GT2

VC-2A

VC-2B

MINERAL SPRINGS NEAR SAN YSIDRO

-13 -12 -11 -10 -9 -8 

DELTA OXYGEN-18 (d 16O), IN PER MIL

-7 -6

Figure 45.--Covariation of deuterium and oxygen-18 in reservoir fluid in Valles Caldera, 

derivative water near Canon de San Diego, and mineral-spring water 

near San Ysidro and Jemez Pueblo (data from Mariner and others, 1977, 

table 5; Trainer, 1978; Truesdell and Janik, 1986, table 3; Vuataz and 

Goff, 1986; Shevenell and others, 1987; and Goff and others, 1992). Well 

and spring locations shown in figures 5 and 41 B.

88
Table 16. Selected streamflow and chloride data and calculations for reach of Jemez River

between U.S. Geological Survey streamflow-gaging station Jemez River near

Jemez (08324000) and San Ysidro, March 1, 1984

[Data from Craigg (1992, table 3); ft3/s, cubic feet per second; mg/L, milligrams per 

liter; g/s, grams per second; NA, not applicable; , no data]

Measurement 

site 

(fig. 41B)

ll

2

23

4

5

36

Distance 

downstream 

(miles)

NA

3.6

~

4.2

8.1

11.2

Discharge 

(tf/s)

37.8

41.3

1.5

37.2

44.2

50.2

Gain (+) or 

loss (-) (f t3/*)

NA

+3.5

-5.6

+7.0

+6.0

Chloride 

concentration 

(mg/L)

47

49

21

48

74

100

Chloride 

load (g/s)

50.3

55.0

.89

50.6

92.6

142.2

1 Jemez River near Jemez. 

2Vallecito Creek (tributary) at mouth. 

Report of quicksand suggests the presence of springs in the riverbed.

Discharge from the Geothermal Reservoir

The concealment of discharge conduits and 

much of the discharge presents a major difficulty in 

estimating geothermal discharge. A somewhat 

mitigating circumstance is that the geothermal 

reservoir(s) seems to discharge only along the 

southwestern rim of the caldera. The known area of 

discharge is bounded laterally by well GT-2 on the west 

and well VC-1 on the east (fig. 5). The areal 

distribution of shallow-temperature gradients in this 

region of the Jemez Mountains (Sass and Morgan, 

1988, fig. 9), which reflects the areal pattern of 

conductive heat flow toward the surface, suggests that 

the area of outflow may extend as much as 2 mi east of 

well VC-1. Thermal data, combined with other 

information on surficial and subsurface geology and 

hydrochemistry, provide a convincing model of the 

region of thermal-fluid outflow (Goffand others, 1988, 

fig. 3; 1992, fig. 6).

Lateral discharge from the geothermal 

reservoir(s) consists of three components heat, 

reservoir fluid, and dissolved load. Several estimates 

have been made of the magnitude of reservoir fluid

discharge. These estimates, based on water chemistry, 

are diverse and difficult to compare with one another; 

all imply a rather small reservoir fluid discharge.

Water Resources Associates, Inc. (1977) 

estimated the total average discharge from the 

reservoir(s) of 164 gal/min from springs and other 

sources not identified and 152 gal/min in base flow at 

the Jemez River near Jemez (08324000) gaging station, 

upstream from Jemez Pueblo. In light of present 

understanding, the spring-flow element is considered to 

be overestimated because dilute water having no 

reservoir component is included. The base-flow 

element is overestimated if it includes spring flow 

already counted, and the total is underestimated 

because the ion-mixing calculation is based on As, a 

nonconservative element in ground-water and stream 

environments. Finally, possible conduit flow is not 

accounted for from Valles Caldera in the reach of 

canyon south of Jemez Pueblo.

Balleau (1980) estimated fluid discharge from 

the Valles Caldera reservoir through ion-mixing 

calculations, using concentrations of eight constituents 

(Cl, F, Br, Na, K, Li, As, and Br) and data from the 

principal sources available at the time (Purtymun and

89
others, 1974; Water Resources Associates, Inc., 1977, 

app. 2; Trainer, 1978; and U.S. Department of Energy, 

1980, tables 3.8 and 3.9). Mixing calculations using 

winter (January 29,1974) measurements of streamflow 

resulted in an estimate of 450 gal/min (about 1 ft3/s) for 

the flow of caldera-derived geothermal fluid carried by 

the Jemez River at Highway 4 between Jemez Pueblo 

and San Ysidro. This is a reasonable estimate and 

constitutes the larger part of geothermal discharge 

down Canon de San Diego to this point. However, 

several uncertainties affect estimation of total 

geothermal fluid discharge at this site.

Total geothermal fluid discharge consists of three 

components: ground-water underflow in alluvium 

beneath the stream channel and canyon floor; conduit 

flow in bedrock, which continues downcanyon; and 

streamflow. Underflow is estimated here to supplement 

the l-ft3/s streamflow value estimated by Balleau 

(1980). As noted earlier, streamflow and Cl data 

reported by Craigg (1992) support a larger estimate of 

the mineral-water component at a gaging station farther 

downstream (Jemez River above Rio Salado). That 

estimate is not discussed here because of uncertainty 

about whether the dissolved load has been brought 

entirely from Canon de San Diego or (as is likely) 

partly from Nacimiento Mountains sources.

At Jemez Pueblo, the canyon has been incised 

into rift-fill deposits of Zia Sand, a sequence of 

siltstone and partly consolidated fine-grained 

sandstone that is about 1,000 ft thick at its type section 

in the hills, 8. mi south-southwest of San Ysidro. The 

Zia Sand locally stands above the floor of lower Canon 

de San Diego as erosional terraces and west of Jemez 

Pueblo as small buttes. At Jemez Pueblo, the thickness 

of Quaternary alluvium penetrated by wells in the 

canyon floor is 100 ft or more, and a well beside the 

river in San Ysidro is reported to have penetrated 7 ft of 

alluvium (Craigg, 1984, table 1). The driller's log for 

the 81-ft well at Jemez Pueblo lists "solid sand" at 77 

to 81 ft, which may be Zia Sand; alluvium is reported 

to be at least 55 ft thick at a bridge site near Jemez 

Springs and also at Jemez Canyon Dam (fig. 1) north of 

Bernalillo (Spiegel, 1962, p. 1, 10). Four wells near 

Battleship Rock, beside the Jemez River at the rim of 

the caldera, penetrate minimum thicknesses of 39 to 80 

ft of alluvium. The log of the geothermal test well at 

Jemez Springs reports 80 ft of alluvium overlying 

bedrock in the canyon floor (Goffand others, 1981).

Thus, the Jemez River alluvium appears to be about 80 

ft thick (and locally may be thicker, perhaps as a result 

of deposition accompanying deformation in areas of 

faulting). The 80-ft value is comparable to 75 ft of 

incision and subsequent backfilling that occurred along 

the Rio Grande at Albuquerque in late-glacial and 

postglacial time (Kelley, 1969, p. 13).

The estimated underflow ranges from 7 to 14 

ft3/s and was determined on the basis of the following 

assumptions: thickness of permeable section, about 

100 ft (the underlying Zia Sand, much less permeable 

than the alluvium, is ignored in this calculation); width 

of section, about 3,200 to 6,400 ft; downcanyon watertable gradient (gradient of river), 15 ft per mile (ft/mi); 

and hydraulic conductivity, about 8.7 x 10"3 feet per 

second (ft/s) (about 750 feet per day (ft/d)). By using an 

intermediate value of underflow of 10 ft3/s and Cl 

concentrations of 100 mg/L for underflow and 2,500 

mg/L for the original reservoir fluid, the balance 

equation used in an earlier discussion (eq. 5, p. 72) 

yields an estimate of 4 percent of the 10-ft3/s underflow 

or 0.4 ft3/s being composed of geothermal fluid from 

the caldera. The total estimated flow of geothermal 

fluid past the site, 1 ft3/s in streamflow and 0.4 ft3/s in 

underflow, or 1.4 ft3/s (628 gal/min), is a reasonable 

estimate for the hydrologic conditions of winter 1974. 

It is an underestimate by the unknown magnitude of 

any conduit flow that continues past (beneath) the site 

and an overestimate to the extent that the area of 

mixing of fluids from Valles Caldera and Nacimiento 

Mountains extends upstream into Canon de San Diego. 

To some degree these opposing "errors" should cancel 

one another.

©©midlyDll FD©w Son iksdlrodk

The pattern and number of known and inferred 

faults in the area north and east of San Ysidro (fig. 1) 

suggest the possibility of additional subsurface flow 

paths from the caldera to the Albuquerque Basin 

through conduits in bedrock. Flow along such routes 

might be verified and the locations of flow paths 

determined within broad limits if increases in 

geothermal-indicator constituent concentrations were 

found in the Jemez River between San Ysidro and the 

Rio Grande, or in the Rio Grande itself.

Anderholm (1988, p. 89) reported several wells 

in Bernalillo, most of them east of the Rio Grande, in 

which the water contains Cl and SiO>2 in concentrations 

that in this region are suggestive of geothermal water. 

He pointed out that these wells are situated on the
projected southward continuation of faults exposed in 

Santa Ana Mesa north and west of the Rio Grande and 

suggested two alternative explanations for the 

anomalous water quality: (1) faults in Santa Ana Mesa, 

which continue southward through bedrock and 

semiconsolidated rift-fill sediments, may be conduits 

for geothermal fluid from Valles Caldera or (2) the 

mineralized water came from Jemez River, infiltrated 

the streambed, and flowed southward in the valley-fill 

aquifer. The fault-conduit explanation is the more 

probable because ground water at shallow depths, 

flowing toward the Rio Grande from the north and 

west, would more likely become part of the underflow 

moving parallel to the river than to pass transversely 

beneath it. The alluvium beneath the river must fill a 

slot incised in the rift fill, as it does in Albuquerque, 

and the greater permeability of the alluvium would 

facilitate the normal underflow downstream. Water in 

fault conduits, however, could cross beneath the river at 

depths greater than the ribbon of alluvium, particularly 

if it were under greater head than the shallow ground 

water near the river.

Dissolved-constituent load from Valles Caldera 

entering the regional aquifer of the Albuquerque Basin 

as conduit flow is less readily dispersed and may form 

bodies of mineralized water within the basin aquifer. 

Such a process is thought to underlie the observations 

reported by Anderholm (1988). Although discussion of 

caldera-derived constituents in earlier sections of this 

report emphasized conservative species such as Li and 

B, which are effective tracers, other constituents such 

as As are of greater interest in issues related to 

domestic and public-water supply.

Recent investigations in the town of Bernalillo 

imply the extent of arsenic in local ground water. Kelly 

and Reinert (1996, p. 481) reported that numerous 

mixed samples of water from the two municipal wells 

east of the Rio Grande had concentrations of As larger 

than 50 micrograms per liter (ug/L) (the maximum 

concentration limit established by the U.S. 

Environmental Protection Agency, 1977). Such 

concentrations explain the finding of As concentrations 

approaching 50 ng/L in Bernalillo Wastewater 

Treatment Plant discharge (Pierce, 1989, p. 35; New 

Mexico Environment Department, 1991, p. 126, 129, 

132). The wastewater, which was pumped from the 

town wells before municipal use, contained 47 (j,g/L As 

on July 25,1988. A suite of samples collected in JuneSeptember 1991 contained 31 to 43 jag/L As; during the 

same period the concentration of As measured in 

discharge from Jemez Canyon Dam ranged from 12 to

21 u£/L. This difference favors the hypothesis that the 

body of mineralized water Anderholm (1988) reported 

in Bernalillo was derived from conduit flow.

Little is known of ground-water quality between 

San Ysidro and the Rio Grande. A few records identify 

wells beside and south of Jemez River in which large 

concentrations of Cl (as much as several hundred 

milligrams per liter) have been reported (Craigg, 1984, 

tables 1, 3; Anderholm, 1988, table 10) and that 

probably reflect infiltration from the Jemez River. 

Kelly and Reinert (1996, tables 1 and 2) presented 

ground-water data for this reach of the Jemez River and 

in Bernalillo west of the Rio Grande that show As 

concentrations to be zoned or banded stratigraphically. 

The smaller concentrations were detected in layers 

shown by geophysical logs to have greater wateryielding potential than other layers, an observation that 

implies greater dilution in the layers that have higher 

transmissivity (Kelly and Reinert, 1996, p. 482).

Streamflow

A series of Streamflow measurements was made 

by the USGS, February 14-15,1974, in the reach from 

Otowi Bridge, just south of San Ildefonso Pueblo, to 

Bernalillo (fig. 1); selected constituent loads were 

determined using concentrations of Cl, Li, and B. The 

study sought to determine (1) the existence of any 

inflow of geothermal fluid from the Pajarito Plateau 

along the east side of the Jemez Mountains (between 

Otowi Bridge and San Felipe) and (2) the presence of 

any inflow downstream from San Felipe (where faults 

appear to be more numerous than in the Pajarito 

Plateau) that cannot be explained by the chemical load 

carried to the Rio Grande by the Jemez River. The data 

and calculated loads of Cl, Li, and B are summarized in 

table 17.

The measurements were made during a period of 

stable Streamflow (table 18). The relation of discharge 

at San Felipe to that at Otowi Bridge is complicated by 

the flow control exerted behind Cochiti Dam between 

the two sites. Nonetheless, given the increase in 

discharge from Cochiti Dam on February 13-14, the 

data in table 18 do not reveal an increase in Cl, Li, or B. 

The subsequent study by Goff and Sayer (1980), which 

used stable isotopes, showed conclusively that there is 

no measurable leakage of geothermal fluid from Valles 

Caldera into the rift-fill deposits beneath the Pajarito 

Plateau.

91
Table 17. Chemical loads for selected ions in the Rio Grande, Otowi Bridge to Bernalillo

[Data from Trainer (U.S. Geological Survey, 1975, 1976, and 1978, table 6). ft3/s, 

cubic feet per second; L/s, liters per second; g/s, grams per second; --, no data]

Streamflowgaging station

Rio Grande at 

Otowi Bridge

Rio Grande at 

San Felipe

Jemez River 

below Jemez 

Canyon Dam

Rio Grande at 

Bernalillo

Discharge

Date

2-14-74

2-14-74

2-15-74

2-14-74

ftVs

1 726

a882

249

Voi

L/s

20,560

24,978

1,388

19,852

Concentration (mg/L)

Cl Li B

9 0.02- 0.05

8 .20 .05

314

24 .11 .14

Load (g/s)

Cl

185

200

436

476

Li B

0.41 1.03

.50 1.25

2.18 2.78

1Measured discharge.

2Mean daily discharge from gage-height record.

Table 18. Mean daily discharge at selected streamflow-gaging stations,

February 11-15, 1974

[Data from U.S. Geological Survey, 1975; all values in cubic feet per second]

Streamflow-gaging station

Rio Grande at Otowi Bridge

Rio Grande below Cochiti Dam

Rio Grande at San Felipe

Jemez River below Jemez Canyon Dam

11

662

650

673

76

12

667

656

683

41

Discharge

13

684

571

582

43

14

706

714

789

70

15

694

695

715

49

92
Dam control also affects the quality of data for 

the river reach between San Felipe and Bernalillo. 

Jemez Canyon Reservoir (fig. 1) is operated for 

desilting and flood control; during the 5-day period 

shown in table 18, releases from the reservoir 

fluctuated more widely than did flow in the main stem. 

In this study all measurements and sampling on the 

main stem of the Rio Grande were completed in a 

single day, but time was not sufficient to visit Jemez 

Canyon Reservoir. Because routine sampling at the 

gaging station below the reservoir was scheduled for 

the next day, the routine sample and the discharge 

calculated from the recorder gage height were used. 

The Cl load entries in table 17 are reasonably 

interpreted to indicate a substantial inflow of Cl to the 

Rio Grande between San Felipe and the mouth of the 

Jemez River. But a calculation using the mean 

discharge at the gaging station Jemez River below 

Jemez Canyon Dam for February 14 (70 ft3/s; table 18) 

yields a load of 622 grams per second (g/s) Cl. Clearly, 

these results are inconclusive: there may be geothermal 

inflow to the Rio Grande, but the increase in Cl load 

observed in the reach from Otowi Bridge to Bernalillo 

can be attributed to Cl load from the Jemez River. 

Determining possible additional subsurface discharge 

from Valles Caldera to the Jemez River east of San 

Ysidro or directly to the Rio Grande will require 

repeating the constituent-load study on the Rio Grande 

downstream from Cochiti Dam and conducting a 

similar study on the Jemez River between San Ysidro 

and the Rio Grande.

The magnitude of geothermal-fluid discharge 

from Valles Caldera has been considered at least twice 

since completion of field work by the USGS in 1975. 

First, because the surface water of the Jemez River 

system is already fully appropriated, any consumptive 

use of water in the development of geothermal power in 

Valles Caldera would require approval by the Office of 

the State Engineer to modify an existing right to permit 

an alternate point of diversion, a new destination, and a 

new purpose of water. Among the findings of a hearing 

into this matter (New Mexico State Engineer, 1980) 

were two conclusions about the geothermal discharge. 

(1) Discharge from the geothermal aquifer (reservoir), 

as measured by increases in selected constituent 

concentrations in the Rio Grande at its confluence with 

the Jemez River, ranges from 1,500 to 2,630 acre-ft/yr 

(approximately 2.0 to 3.6 ft /s), with an average value 

of 2,030 acre-ft/yr (2.8 ft3/s). Of this discharge, 523 to 

730 acre-ft/yr (approximately 0.7 to 1.0 ft3/s), with an

average of 632 acre-ft/yr (0.86 ft3/s), reaches the Jemez 

River between the East Fork Jemez River and San 

Ysidro. This conclusion was based on a presentation by 

W.P. Balleau for the protestant Bureau of Indian 

Affairs. Whether the data were adjusted to account for 

constituents contributed by drainage from the 

Nacimiento Mountains is not clear. (2) There is no 

contribution from the geothermal aquifer to the Rio 

Grande upstream from the confluence of the Rio 

Grande and the Jemez River.

Moreover, Faust and others (1984, p. 605), in the 

design of a numerical model of the geothermal system 

in Valles Caldera, used earlier conclusions by Balleau 

(1980) that (1) the total thermal-fluid contribution to 

the Jemez River upstream from San Ysidro is 724 acreft/yr (about 1 ft3/s) and (2) the constituent balance 

implies an annual accretion to the Rio Grande between 

Otowi Bridge and Bernalillo (including the Jemez 

River) of 2,580 acre-ft (about 3.5 ft3/s) of fluid having 

an original concentration equal to that of Jemez 

Mountains geothermal water. Faust and others (1984, 

p. 605) recognized that contributions from Nacimiento 

Mountains sources change the constituent balance in 

the Jemez River downstream from San Ysidro.

Perched Ground Water in Bedrock

Perched ground water has been identified by 

drilling; other areas of perched ground water, however, 

particularly the larger zones, are known from springflow and chemical data. Doubtless many perched zones 

of limited thickness and area are as yet undiscovered.

Two principal types of perched ground-water 

reservoirs in bedrock were noted in an earlier 

discussion: (1) those within volcanic rocks that overlie 

relatively impermeable rock and (2) those within 

sedimentary rocks that are underlain by less permeable 

beds in the same formation. Reservoirs of the first type 

are a typical product of the particular volcanic history 

of this region. The Abo Formation sandstone, shale, 

and siltstone was exposed at the surface over much of 

the landscape on which the Bandelier Tuff, a younger 

volcanic unit, was deposited. Although the prevolcanic 

land surface must have been modified by avalanches 

and other catastrophic effects of the eruptions, the 

major land-surface features doubtless were preserved 

beneath the tuff except perhaps near the crater. Crosssectioned remnants of the ancient landscape can now 

be seen as the Abo-Bandelier unconformity exposed 

locally in the walls of Canon de San Diego. Except for

93
their general slope away from the volcano, few 

additional details are known of the buried landscape, 

although several observations suggest their gross form.

First, without exception the perched water is old. 

In three warm-water springs within the ring-fracture 

zone (P-9, H-39, and H-42; fig. 7), tritium 

concentrations in eight samples (Trainer, 1978; Vuataz 

and Goff, 1986) ranged from 0.2 to 5.1 TU and 

averaged 1.0 TU; five values were less than 0.4 TU.

Second, in these three warm-water springs, 

constituent concentrations are small but have a 

tendency toward cyclical fluctuation reminiscent of 

that described in an earlier section on mineral water at 

Soda Dam and Jemez Springs. This probably means 

that each spring system is recharged at a small number 

of discrete places rather than over the general drainage 

area. Consistent with this observation, the tritium 

values for each spring mostly consist of a large value 

and two smaller values, rather than similar 

concentrations; for example, at Spence Spring (H-42) 

near Battleship Rock the three values are 0.2, 0.2, and 

1.9TU.

Third, in terms of stable isotopes the water falls 

on the meteoric-water line (Vuataz and Goff, 1986). 

This means that recharge is from land surface and that 

no component of geothermal water is of deep origin.

These observations support a conceptual model 

of a long and narrow reservoir not a single body of 

that shape but rather an interconnected series of 

segments consistent with the former drainage net on 

the Abo Formation surface. Recharge from the present 

land surface on the volcanic rocks occurs at only a few 

places in each system, probably through fractures or 

along boundaries between flows. For the three warmwater spring systems, the present topographic relief is 

large; the thickness of volcanic rocks in the flow system 

and the depth of circulation may be many hundreds of 

feet. The areas involved are not known but are probably 

large enough for total relief on the Abo Formation 

basement in each system to reach several hundred feet. 

In these systems ground water is warm because of high 

conductive heat flow from the underlying host rocks.

Several spring systems in the Bandelier Tuff 

located farther down Canon de San Diego display the 

major characteristics just described. The springs are 

situated at low points on the unconformity between the 

tuff and the Abo Formation. Recharge is thought to be 

by infiltration through fractures from the mesa 

surfaces.

Finally, observations during the drilling of well 

GT-2 led to the drilling of a shallow water-supply well 

at the Fenton Hill site (fig. 10). The well yielded water 

from two volcanic-rock units, the Abiquiu Tuff and the 

Paliza Canyon Formation, which overlie the Abo 

Formation and underlie the Bandelier Tuff. 

Observation wells were drilled nearby for use in 

aquifer tests.

Two series of aquifer evaluations were made, one 

by American Ground Water Consultants, Inc. (1980a, 

b), the other by Los Alamos Scientific Laboratory 

(Becker and others, 1981). American Ground Water 

Consultants, Inc. estimated that induced infiltration is 

likely to result from pumpage from the shallow supply 

well. Transmissivity was determined to be 7,000 

gallons per day per foot (gal/d/ft) (935 ft2/d), later 

revised to 1,740 gal/d/ft (230 tf/d). The storage 

coefficient was assumed to be 1 x 10"5 . By assuming a 

rate of withdrawal of 10 acre-ft/yr for 10 years, 

American Ground Water Consultants, Inc. (1980a, b) 

estimated that stream depletion (induced infiltration) in 

the Rio Cebolla (in the Rio Guadalupe Basin) after 1, 

5, 10, and 20 years would be 0.06, 6.9, 15.0, and 6.3 

acre-ft/yr, respectively.

Los Alamos Scientific Laboratory (Becker and 

others, 1981) projected aquifer response to future 

pumping and estimated the transmissivity to be 5,000 

gal/d/ft (670 ff/d) and the storage coefficient to be 

7 x 10"2. For a total projected water use of about 480 

acre-ft (156.4 x 106 gal) from 1981 through 1985, the 

total water-level decline in the supply well was 

projected to be 41.6 ft. Actual withdrawal was 

somewhat different than projected withdrawal. 

Purtymun and others (1988, p. 14-15) reported an 

average annual withdrawal (1976-86) of about 

5 x 106 gal that resulted in a water-level decline over 

the same period of about 17 ft.

QUANTITATIVE MODELING OF THE 

GEOTHERMAL SYSTEM

Various investigators have constructed 

quantitative models of the geothermal system in the 

Valles Caldera and surrounding region. The models 

represent combinations of (1) a conceptual framework 

of geologic and hydrologic conditions and (2) a 

mathematical representation of fluid flow, and 

sometimes heat flow, within the conceptual framework. 

In this section of the report, these two items are referred 

to as conceptual and numerical models, respectively.

94
These existing models were developed primarily to 

provide assessments of reservoir productivity and 

longevity and the potential effects of development on 

thermal-water discharge to the Jemez River. Sufficient 

geologic and hydrologic data are available for this 

region to develop both simplified (one- and twodimensional) models and more detailed (two- and 

three-dimensional) models but not to adequately 

calibrate or test any of the models. As with other 

geothermal areas, the information needed to calibrate 

or test a model generally requires some level of 

exploitation of the geothermal reservoir and the 

resulting changes in the hydraulic and thermal regimes 

adequately delineated by monitoring.

Considering the above conditions, these model 

studies produced a wide range of answers related to the 

response of the hydrothermal system to development. 

Although geothermal fields in other parts of the world 

can provide insight into responses that might be 

expected for the Valles system, each geothermal field is 

sufficiently different that predevelopment predictions 

involve uncertainty. This is perhaps best exemplified by 

the unsuccessful attempt of Union Oil Company and 

the DOE to delineate a resource large enough to supply 

a planned 50-megawatt demonstration power plant, 

despite a favorable geologic setting (young silicic 

caldera in a region of extensional tectonics) and 

favorable temperature and productivity conditions in 

some wells.

This section briefly describes the main features, 

results, and limitations of existing models of the Valles 

geothermal system and outlines the elements required 

for successful modeling of the natural and exploited 

states of this system. However, a successful model of

this type is one that can be modified or adjusted to 

simulate changes observed during at least the early 

stages of development.

Conceptual Models of the Geothermal 

System

Grant (1979) first suggested that the Valles 

system and other systems in areas of large topographic 

relief that overlie zones of upflow of deep, highenthalpy fluid are liquid dominated with a parasitic 

vapor-dominated zone, following the model for the 

geothermal system at Lassen Volcanic National Park, 

California (Ingebritsen and Sorey, 1985). The essential 

elements of this model (fig. 46) include an upflow zone 

and a region of two-phase (boiling) conditions at which 

steam and liquid phases separate, with steam rising 

through a vapor-dominated zone to discharge at high 

altitudes and liquid flowing laterally to discharge as 

springs and river seepage at low altitudes. Fluid 

pressures are distributed with depth as vaporstatic 

(region A), hydrostatic (region B), and 

superhydrostatic (region C). Actual gradients and 

pressures at each geothermal area depend on rock 

properties and fluid flow rates, but this general model 

accounts for several important features of this type of 

system: (1) discharge of neutral-pH, high-chloride 

water in thermal springs at considerable distance from 

the deep, high-temperature reservoir; (2) apparent 

underpressured conditions in the wells completed in 

the deep reservoir; and (3) hydrologic connections 

between areas of steam-heated thermal features, areas 

of high-chloride thermal springs, and underlying hightemperature liquid reservoir(s).

Fumaroles and acid-sulfate discharge 

A

PRESSURE

Chloride springs

B

Liquid outflow 

plume

Phase 

separation

High-enthalpy 

upflow

Figure 46. --Generalized pressure-altitude relations for liquid-dominated hydrothermal systems 

(modified from Grant, 1979).

95
Grant and others (1984) delineated a vertical 

pressure gradient of 24.4 bars/1,000 ft within the 

Redondo Creek subsystem or reservoir from analyses 

of well-bore measurements. Thermodynamic relations 

indicate that upflow would occur in regions where 

temperatures exceed 260 °C. This pressure gradient 

also extrapolates to zero pressure at an altitude of 7,900 

ft, which is about 1,100 ft below land-surface altitudes 

in the Redondo Creek Graben, but about 1,500 ft above 

the level of thermal-spring discharge at Jemez Springs. 

This demonstrates how the geothermal reservoir can 

appear to be underpressured with respect to local landsurface altitudes but have enough head to drive what 

Goffand others (1988) referred to as a hydrothermal 

discharge plume. Well VC-1 (fig. 5) penetrated the 

discharge plume in the caldera's southwest moat; fluid 

samples from this well are chemically very similar to 

fluids sampled from the Redondo Creek wells. Flow 

conduits between the geothermal reservoir and distant 

areas of thermal-water discharge at a low altitude allow 

the reservoir to effectively be underpressured so that 

boiling and phase separation can occur at depth and a 

zone of steam upflow under vapor-static pressure 

conditions can develop. Studies reported by Goffand 

Shevenell (1987) and Goffand others (1992) of the 

ages of travertine spring deposits in Canon de San 

Diego and fluid inclusions in well cores suggest that the 

present-day Valles hydrothermal system evolved over 

the past 0.5 Ma, following a depressurizing event 

associated with breaching of the southwest caldera wall 

and draining of intracaldera lakes.

This basic model for the Valles geothermal 

system needs to be modified to account for 

complications related to heterogeneity in 

thermodynamic and hydrologic conditions within the 

reservoir part of the system. For example, there appear 

to be separate productive zones at different depths 

within the Redondo Creek Graben area, although the 

well-pressure data interpreted by Grant and others 

(1984) suggest a degree of pressure communication 

between wells that penetrate different productive 

zones. Some measure of hydrologic separation may 

occur between the Redondo Creek area (graben) and 

the Sulphur Creek/west moat areas. Grant and others 

(1984) suggested, for example, that differences 

between the altitude of acid-sulfate springs in the 

Sulphur Creek area and the potentiometric surface in 

the Redondo Creek area are associated with the 

presence of a steam-dominated (vapor-static pressure) 

zone beneath the Sulphur Creek area and the absence of

such a zone beneath the Redondo Creek area. Grant 

and others further suggested that the main zone of highenthalpy upflow is northwest of the Redondo Creek 

area and that this fluid flows laterally toward the 

Redondo Creek reservoir.

Goffand others (1992) used information from 

the more recently drilled wells VC-2 A and VC-2B (fig. 

5) and older wells in the west moat and beneath the 

Jemez Plateau west of the caldera to suggest that two 

separate subsystems, beneath Redondo Creek and 

Sulfur Creek, have developed in their own structural 

traps with separate recharge/discharge regimes. 

Furthermore, consistent differences in fluid chemistry 

observed between wells in the western part of the 

caldera and wells in the central part of the caldera 

imply the existence of two different discharge plumes, 

one flowing out the southwestern rim of the caldera and 

down Canon de San Diego and the other flowing across 

the western rim and beneath the Jemez Plateau (Fraser 

Goff, oral commun., 1996). Although fluid in the latter 

plume may ultimately discharge to the Jemez River, its 

larger concentrations of conservative constituents 

(used in constituent-balance calculations to estimate 

thermal-water discharge to the river) could cause the 

total discharge to be overestimated by 10-15 percent.

An additional complication is the presence of 

noncondensible gas (C0>2) in the reservoir fluid at 

Valles Caldera. Although concentrations of CO2 in this 

reservoir fluid have not been adequately delineated 

from existing sampling and wellhead measurements, 

sufficient amounts of gas appear to greatly extend the 

depth over which the vapor-phase condition occurs 

naturally and possibly to influence reservoir drawdown 

during development.

Numerical models of the Valles system and its 

response to development were described by Hartz 

(1976); Water Resources Associates, Inc. (1977); 

Balleau (1980); M.S. Gulati (Union Oil Company, 

written commun, 1980); Francis West (Office of the 

State Engineer, written commun., 1980); Union 

Geothermal Company of New Mexico (1981); 

Bodvarsson and others (1982); and Faust and others 

(1984). These models range in complexity from onedimensional, single-phase fluid-flow models to threedimensional, multiphase fluid and heat-flow models. 

Faust and others (1984) noted that differences in 

modeling approaches used in these studies resulted in a
range from about 6.3 to 1,240 gal/min for the 

calculated depletion of thermal-water discharge to the 

Jemez River from 30-year simulations of geothermal 

development at the 50-megawatt level. (Most 

investigators reported depletion values in units of 

grams per second or kilograms per second; a fluid 

density of approximately 1 gram per cubic centimeter 

was assumed to convert the discharges into volume per 

unit time.) The models of Bodvarsson and others 

(1982) and Faust and others (1984), which are the only 

models that simulate possible production and injection 

scenarios over a 30-year period, give considerably 

different results of predicted reservoir drawdown and 

reservoir productivity over time.

The comparisons of Faust and others (1984) and 

Grant and others (1984) are summarized and values are 

indicated for thermal-water depletion and reservoir 

drawdown predicted by each study in table 19. The 

one-dimensional and (or) analytical models involve 

assumptions of constant net mass production from the 

Redondo Creek reservoir and uniform (but different) 

properties in the reservoir and outflow zones. The 

numerical model produced by the New Mexico State 

Engineer Office (1980) allows for two-dimensional 

fluid flow and variable hydraulic properties in the 

reservoir and outflow zones. The three remaining 

numerical models (Union Geothermal Company of 

New Mexico (1981); Bodvarsson and others (1982); 

and Faust and others (1984)) allow for multiphase fluid 

flow (steam and water) and heat flow in two or three 

dimensions and include specifications for inputs of 

high-enthalpy liquid at the base of the reservoir. All 

models are based on the assumption that zones of fluid 

flow, although containing regions of fracturecontrolled flow, can be treated as porous media at the 

scale of the model.

Considering the range of complexities in the 

different models, the results of predicted thermal-water 

depletion in the discharge in the Jemez River are not 

significantly different, except for the models of Hartz, 

Gulati, and Union Geothermal Company of New 

Mexico. The latter two models predict much less 

depletion because of inadequate treatment of twophase effects in the reservoir or insufficient simulation 

time. For the models by the New Mexico Office of the 

State Engineer; Water Resources Associates, Inc.; and 

Balleau differences in depletion predictions, from 365 

to 1,240 gal/min, could have been reduced and the 

predicted values brought more in line with that of the 

more complex three-dimensional simulation of Faust 

and others (1984) by adjusting assumed flow-zone

parameters that could be justified with existing 

subsurface data. This raises the question of whether a 

more complex model is needed to address the effects of 

development on thermal springs. This issue is 

discussed in the final part of this section.

For simulations of changes in reservoir 

conditions and well productivity during development, 

the basic difference between the models of Faust and 

others (1984) and Bodvarsson and others (1982) is that 

in the former the reservoir is subdivided into four layers 

and in the latter it is treated as a single layer. Other 

differences are in assumed reservoir areas, total 

thickness, and permeability-thickness products. In 

general, the two-dimensional areal model of 

Bodvarsson and others yielded predictions of greater 

reservoir drawdown and shorter longevity than did the 

three-dimensional model of Faust and others (1984). 

Faust and others considered these differences to result 

primarily because Bodvarsson and others (1982) used a 

smaller permeability-thickness product and ignored 

vertical variations in thermodynamic conditions (steam 

fractions) within the reservoir.

Quantitative Constraints

Validation of the accuracy and applicability of 

predevelopment models requires a comparison of the 

models with quantitative constraints on the geothermal 

system. Such constraints typically are provided by 

measurements and estimates of rates of recharge and 

discharge of thermal fluid, hydraulic and thermal 

properties of reservoir rocks and fluids, and geologic 

and topographic controls on the geometry of the flow 

system. For the Valles geothermal system, enough 

information is available to construct scientifically 

defensible preliminary models at various levels of 

complexity, but not to provide enough quantitative 

constraints to adequately calibrate or test these models. 

What is still needed is some period of actual 

development in which the system is stressed and 

hydrologic changes are measured. This common 

situation is one for which preliminary models can still 

be useful for evaluating and designing potential 

development scenarios and monitoring schemes. Under 

such conditions, however, models cannot be expected 

to provide accurate answers to questions involving 

long-term changes to the hydrothermal system, 

including effects on surface features.
Table 19. Summary of characteristics and results of existing quantitative models

of the Valles hydrothermal system

[gal/min, gallons per minute; ND, not determined; ~, approximately; , no data]

Predicted 

thermal-water

depletion1 in 

discharge in

Predicted

reservoir

Investigator Model type Assumptions

drawdown after Jemez River 

30 years (feet) (gal/min)

Hartz (1976)

Water Resources 

Associates, Inc. 

(1977)

Balleau (1980)

Gulati5

New Mexico State 

Engineer Office

(1980)1

Union 

Geothermal 

Company of New 

Mexico (1981)

Analytical, zero 

dimensional2

Analytical, one 

dimensional

Analytical, one 

dimensional

Analytical

Numerical, two 

dimensional

Numerical, three 

dimensional

Two-phase 

lumped 

parameter model

Single phase, 

wedge shaped

Single phase, 

radial flow

Two phase 

Single phase

Two phase

3(~200)

ND

*690

(-200)

190

824

1,240

33

365

ND

Bodvarsson and 

others (1982)

Faust and others 

(1984)

Numerical, two 

dimensional

Numerical, three 

dimensional

Two phase, 

areal model

Two phase

6(~2,560)

7560 - 1,710

ND

697

Values reported by different authors were converted to gal/min assuming fluid densities of about 1 

gram per cubic centimeter. Value listed for Hartz (1976) was estimated from the finding of the New 

Mexico State Engineer Office (1980) that thermal-water depletion would be 15 percent of initial thermalwater discharge (here assumed to be 1,270 gal/min). Value listed for Water Resources Associates, Inc. 

(1977) is the adjusted value cited in Balleau (1980). Value listed for Union Geothermal Company of New 

Mexico (1981) is based on a 5-year simulation that showed increases in thermal-water discharge in the 

Jemez River (although the rates declined with time).

2Zero dimensional refers to a box model with uniform properties and response to development. 

3~200 represents the difference in head between initial single-phase reservoir pressure and the head 

corresponding to pressure on the boiling point.

Calculated for a radial distance of 0.25 mile from the production source.

5M.S. Gulati, Union Oil Company of California and Public Service Company of New Mexico, written 

commun., 1980.

6~2,560 represents the difference in head between initial reservoir pressure (85 bars) and an abandonment 

pressure of 10 bars. 

'Values listed are those given for different production nodes.

98
Information available for the Valles system 

allows estimates to be made of the rates and locations 

of thermal-water discharge inside and outside the 

caldera, ranges of values for hydraulic and 

thermodynamic properties in the geothermal reservoir, 

and variations of possible geometric configurations for 

the areal and vertical extent of the reservoir and 

associated upflow zones. Of these values, the most 

accurately known appear to be those for thermal-water 

discharge in the Jemez River and for reservoir 

temperature and pressure distributions. Model 

simulations of changes in thermal-water discharge 

have for the most part yielded consistent results, in part 

because such predictions do not depend as much on 

detailed knowledge of conditions within the caldera. In 

contrast, the greater uncertainty in values and 

distributions of hydraulic properties of rocks and 

geologic limits on the flow system within the caldera 

has resulted in widely differing results from model 

simulations of reservoir response to development.

Results of constituent-balance calculations 

applied to the Jemez River and the Rio Grande show 

the following ranges of values for thermal-water 

discharge from the Valles hydrothermal system 

(Balleau, 1980; New Mexico State Engineer Office, 

1980).

Site Thermal-water discharge

Jemez River above San Ysidro 320-620 gal/min 

Jemez River at Rio Grande 900-1,580 gal/min

The increase in thermal input downstream from 

San Ysidro apparently indicates that the zone of 

thermal-water discharge from the caldera is broad (not 

confined to Canon de San Diego) and may include 

separate conduits at different depths. There may also be 

inputs of tracer ions (such as Cl and B) from 

nonthermal sources within the drainage of the 

Nacimiento Mountains. Also, these calculations ignore 

the possibility of more than one reservoir source for the 

thermal water, as might be the case if discharge derived 

from the Sulfur Creek subsystem with somewhat 

different chemical composition flows westward and 

then southward eventually to enter the Jemez River. 

Nevertheless, the previous estimates provide useful 

constraints on models of the geothermal system, 

especially those constructed to evaluate the effects of 

geothermal development on natural thermal-water 

discharge.

Modeling studies by Faust and others (1984) and 

Balleau (1980) include somewhat independent 

calculations of thermal-water discharge under 

predevelopment conditions. In fact, the estimate of 

Faust and others (1984) of 790 gal/min for total 

thermal-water discharge from the hydrothermal system 

has been cited by some as the "best" value for this 

quantity. Although Faust and others said that their 

estimate was obtained by adjusting thermal-water 

throughflow within the reservoir to produce a match to 

known pressure and temperature distributions, a midrange (compared to constituent-balance results) value 

of 1,270 gal/min was possibly chosen for thermal input 

at the base of the model, and various properties (such 

as vertical permeability and thermal conductivity) were 

possibly adjusted to provide satisfactory matches to 

pressures and temperatures. Their model then 

simulates a total flow through the system and 

subsequent discharge to the Jemez River of 

approximately 790 gal/min. This estimate is not so 

much an independently derived constraint as it is an 

indication that this model provides reasonable matches 

to predevelopment conditions.

Similarly, Balleau (1980) estimated the thermalwater discharge to the Jemez River upstream from San 

Ysidro to be 745 gal/min, based on an equation derived 

from Darcy's law and taking into account estimates of 

transmissivity of the geothermal reservoir and head 

loss within the thermal flow system between the 

reservoir and San Ysidro. Balleau's estimated 

discharge is close to the estimated discharge of 628 

gal/min presented in the "Ground-water underflow" 

section (p. 90) of this report. Because of the uncertainty 

in actual values for each property used in the 

calculations (as well as limitations inherent in the 

simplified approaches), however, results differing by a 

factor of two could also be justified. Thus, this result 

serves mainly to indicate that discharge from the Valles 

geothermal system can reasonably account for the 

inputs of conservative constituents into the Jemez 

River.

Modeling System Response to 

Development

In general, the best approach to modeling 

systems such as the Valles geothermal system and its 

response to geothermal development is based on a 

viable conceptual model of the hydrogeologic 

framework that incorporates as much known 

information about the system as is required to

99
adequately validate the model against the available 

quantitative constraints. The most detailed model is not 

always the best. For example, a numerical model with 

tens of thousands of grid blocks may be too 

cumbersome (and expensive) to test the sensitivity of 

model results to alternative boundary conditions or to 

variations in model properties. At the other extreme, a 

simple, one-dimensional analytical solution for 

drawdown and streamflow depletion tends to be too 

poorly constrained to offer any quantifiable measure of 

the accuracy of its predictions; this could change, 

however, if the response of the system to production 

was measured during the early stages of development.

Elements necessary for successful modeling of 

this type of system include (1) three-dimensional 

descriptions of fluid and heat flow that can treat both 

lateral and vertical heterogeneities, (2) a multiphase 

thermodynamic and fluid-flow formulation, (3) 

hydrologic continuity between the geothermal 

reservoir and the discharge plume of thermal water in 

areas inside and outside the caldera, (4) capability to 

allow for variable input rates of high-enthalpy fluid into 

the geothermal reservoir, and (5) capability to treat 

different production/injection scenarios as affected by 

changes in steam fractions in regions around 

production wells. The model of Faust and others (1984) 

has these capabilities yet is simple enough that it can be 

used to test combinations of different parameters or to 

examine the importance of two-phase effects and 

vertical variations in reservoir properties and fluid 

(thermodynamic) states in modeling the reservoir 

response to development.

For two-phase effects, early modeling studies 

carried out by Union Oil Company predicted that 

reservoir pressures would decline during development 

until the fluid reached the boiling point and that 

subsequently reservoir pressures would cease declining 

because of the large effective compressibility of twophase fluid. Because the high-temperature reservoir 

fluid at Valles initially is close to the boiling point, this 

type of analysis predicts little drawdown of reservoir 

pressure and hence predicts only minor declines in 

thermal-water discharge outside the caldera. This 

reasoning appears to have formed the basis for the 

finding by the New Mexico State Engineer Office 

(1980) that the decrease in thermal-water discharge 

upstream from San Ysidro would amount to only about 

15 percent following geothermal development. More 

recent numerical model studies have clearly 

demonstrated that the formation of two-phase zones in 

response to production would be localized around

production wells and not spread uniformly through the 

reservoir. Consequently, reservoir drawdown would 

not stop when the boiling point is reached and may in 

fact accelerate because of the nature of steam/water 

relative permeability functions.

The more detailed numerical models have 

demonstrated that injection of liquid in wells south and 

southwest of production wells in the Redondo Creek 

Graben may actually result in pressure increases and 

increases in thermal-water discharge to the Jemez 

River during the first few years of injection. This effect 

is overcome in later model simulation years by the 

spread of the drawdown region created by the 

production wells. These results imply, however, that 

placement of some injection sites closer to the thermal 

springs along the Jemez River could ultimately be used 

to prevent negative effects on these springs from longterm geothermal development.

The detailed numerical models of Faust and 

others (1984) and Bodvarsson and others (1982) 

predict significantly different reservoir response to 

development in terms of degree of drawdown and 

longevity of the field (time period until reservoir 

pressure falls too low to sustain adequate steam 

production). Faust and others (1984) criticized the 

earlier results as overly pessimistic because the value 

of reservoir thickness used was too small and because 

vertical variations were not considered. Subsequent 

events, however, suggest that the earlier study that cast 

doubt on the ability of the Valles system to sustain a 50- 

megawatt power plant may have had some validity.

Interestingly, the greatest reservoir longevity in 

the study by Bodvarsson and others (1982) involved 

input of hot water at the base of the model at rates that 

increased with time from 0 to 790 gal/min. Similarly, 

this recharge of hot water is also an important aspect of 

the model of Faust and others (1984), who settled on a 

constant input of 1,050 gal/min. In the undeveloped 

state, this input supplies the throughflow of thermal 

water that ultimately discharges in thermal springs or 

streams. Experience gained modeling other systems 

following periods of development indicates that the 

rate of thermal-water input likely will increase as a 

result of pressure declines in the reservoir during 

development. In some cases, this increased input can 

become a very significant fraction of the net fluid 

produced and hence can exert a strong influence on the 

level of drawdown. Also, reservoir drawdown could 

induce inflow of cooler water from shallower regions 

into the production zone. Neither of these processes has
been simulated in the modeling studies thus far 

completed for the Valles system.

Finally, existing models do not account for the 

presence of C(>2 in reservoir fluid. During model 

development, Grant and others (1984) suggested that 

reservoir pressure changes could be significantly 

influenced by the presence of dissolved gas. They cited 

the example of the Broadlands field in New Zealand 

where gas contents were twice as large as at the Valles 

geothermal system and pressure changes during the 

early stages of production were dominated by gas 

partial-pressure effects. The numerical study by 

Pritchett and others (1981) indicates that such effects 

increase the two-phase region near production wells 

and increase reservoir pressure declines. Faust and 

others (1984) suggested that the actual distribution of 

CC>2 concentrations in Valles reservoir fluids is not 

adequately known and that some indications of large 

gas concentrations in water sampled from wells may 

not actually exist in the liquid-dominated parts of the 

reservoir. This matter requires further study because 

more accurate simulation of reservoir performance and 

longevity is needed and because model predictions of 

changes in thermal-water discharge are strongly 

dependent on the level and distribution of reservoir 

drawdown resulting from development.

MONITORING HYDROCHEMICAL 

DISCHARGE IN THE SOUTHWESTERN 

JEMEZ MOUNTAINS

Development of geothermal energy in or near 

Valles Caldera possibly would change the 

hydrochemical discharge from the southwestern Jemez 

Mountains. Detection of and tracking such change 

would require systematic monitoring. The information 

gained from such monitoring would be valuable in 

better understanding the geothermal system and in 

testing, refining, and calibrating numerical models of 

the system. Several components of a monitoring 

system are already available as a result of past and 

ongoing data collection in the region (table 20). 

Extension and some modification of these activities 

could provide monitoring of most chemical transport in 

surface water and much of the transport in ground 

water.

Effective monitoring of a complex 

geohydrologic system requires prior understanding of 

the system. In many areas, including the Jemez 

Mountains, the knowledge available initially may be 

inadequate for the design of all aspects of a monitoring

plan, and the plan may need some modification as the 

work progresses. For this reason, and because of the 

desirability of a period of record antecedent to 

anticipated development, a monitoring program would 

need to begin as promptly as is practicable after the 

need for it has been recognized.

Surface drainage, which receives much of the 

subsurface drainage before leaving this region, is 

accomplished by the Jemez River and its tributary, the 

Rio Guadalupe. The combined flow of these streams, 

which join north of Canon and Jemez Pueblo (fig. 47), 

is measured at the USGS streamflow-gaging station 

Jemez River near Jemez (08324000).

Two principal tributaries of the Jemez River 

drain Valles Caldera: San Antonio Creek drains the 

northern moat area and its adjacent slopes and the East 

Fork Jemez River drains the southern moat area and its 

adjacent slopes. Both are fed principally by dilute 

spring waters of shallow origin, but San Antonio Creek 

also receives the flow of two small streams from the 

west side of Redondo Peak Sulphur and Redondo 

Creeks. Sulphur Creek flows through the Sulphur 

Springs area, and Redondo Creek drains the faulted 

terrain on Redondo Peak where most of the exploratory 

geothermal drilling has been done. Upstream from 

Soda Dam these small streams contribute much of the 

SO4 and Cl carried by the Jemez River; downstream 

from the dam the mineral springs at Soda Dam and 

Jemez Springs contribute most of the dissolved load.

The Rio Guadalupe drains much of the region 

west and southwest of the caldera. It contributes, on 

average, about two-thirds of the streamflow recorded at 

Jemez River near Jemez but about half the dissolvedconstituent load. Abundant data for Rio Guadalupe 

Basin show no evidence of a natural geothermal 

contribution to streamflow and dissolved load. 

Geothermal effluent detected at the Jemez River near 

Jemez (08324000) site is transported by the Jemez 

River upstream from the junction with the Rio 

Guadalupe.

Hydrochemical changes in the Jemez River and 

Rio Guadalupe systems can be identified and tracked 

most effectively by monitoring streamflow and water 

quality at selected gaging stations and supplementing 

those observations with surface- and ground-water data 

within their corresponding basins. Data collected at 

Jemez River below East Fork, near Jemez Springs 

(08321500), for example, indicate changes in 

hydrochemical discharge during the last 30 years; 

consideration of these records provides insight into the 

monitoring problem.

101
Table 20. Selected periodic measurement sites at which streamflow and 

water-chemistry data have been collected

Site 

identifier 

(fig. 47)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Site name

San Antonio Hot Spring

San Antonio Creek above Sulphur Creek

Sulphur Creek above Redondo Creek 

Redondo Creek above Sulphur Creek 

(near gaging station 08319945) 

Sulphur Creek above San Antonio Creek 

(near gaging station 083 19950)

Wells and springs near La Cueva

Spence Spring

Jemez River above East Fork

Jemez River below East Fork 

(gaging station 08321500)

McCauley Spring

Limestone Spring near Battleship Rock

Test well near Battleship Rock

Sino Spring

Agua Durme Spring

Springs at Soda Dam 

Jemez River above Soda Dam

Jemez River below Soda Dam

Springs in Church Canyon

Jemez Springs 

Jemez Springs below Jemez Springs

Jemez River above Rio Guadalupe

Spring (tank), Lake Fork Canyon

Stream sampling sites in Lake Fork Canyon

Spring, Lake Fork Canyon

Rio Cebolla below Lake Fork Canyon

Rio Guadalupe above Jemez River

Jemez River near Jemez

(gaging station 08324000)

Jemez River at Highway 4 near San Ysidro

Discharge 

data1

No

No

No 

No

Yes

No

No

Yes 

Yes

Yes

No

No

No

No

Yes

Yes

Yes

No

Yes 

Yes

No

No

No

No

No

No

Yes

No

Source of 

chemical 

data2

L

L,G

L 

L

L,G

L

L

L,G 

L,G

L,G

G

G

G

L

L, G 

G

G

L

G 

G

L

L

L

L

L

L

L, G

G

Discharge measurements by the U.S. Geological Survey.

2Agency collecting water-chemistry data: L, Los Alamos National Laboratory; G, U.S. Geological Survey.

102
106°50' R ,g_ ARR|BA_ _COUNTY 

SANDOVALCOUMtY

106°30'

08321500 

Soda <5?ef 2 .13

R. 1 E.

10 MILES

10 KILOMETERS «=

4 R.5 E.

EXPLANATION

U.S.GEOLOGICALSURVEY

STREAMFLOW-GAGING STATION

PERIODIC-MEASUREMENT 

SITE-Site identifier in table 20

Figure 47.-Selected streamflow-gaging stations and periodic-measurement sites 

where hydrologic measurements have been made.

103
HISTORICAL MONITORING

The Cl load at the Jemez River below East Fork, 

near Jemez Springs for 1963-67 and 1971-82 is plotted 

in figure 4B. The 1963-67 chloride loads are in two 

overlapping groups with respect to magnitude. Cl load 

in the two groups is similar, but the more abundant 

samples containing smaller loads are characterized by 

low stream discharge (mean about 13 ft3/s). The few 

samples containing large loads occur at higher 

discharge (mean about 32 ft3/s). The smaller stream 

discharge occurs when ground-water inflow to the 

stream provides all or most of the base flow. The larger 

stream discharge represents periods of surface runoff 

from storms and melting snow. Considering the range 

in conditions and the few data available, particularly 

for the larger discharge, determining a representative 

mean value for Cl load is difficult. The dashed trend 

line in figure 48, extending through the group of 

smaller values for 1963-67, implies that the magnitude 

of Cl load was relatively stable during periods of base 

runoff.

Further examination of chloride-load plots 

requires consideration of the source of Cl transported

by the Jemez River past gaging station 08321500 (fig. 

47). Atmospheric deposition by rain and snow accounts 

for the larger part of Cl found in dilute water in the 

Jemez Mountains. Chloride also may be derived from 

the near-surface rocks by weathering, but that process 

is unimportant quantitatively because Cl occurs in the 

volcanic rocks in only trace concentrations (Gardner 

and others, 1986).

Chloride concentration in 144 samples collected 

from springs and headwater streams fed by shallow 

ground water (Purtymun and others, 1974-76, 1978, 

1980a, b, 1981,1983; Trainer, 1978, table 5; Shevenell 

and others, 1987, table B-II) ranges from less than 1 to 

14 mg/L (mean value 4.7 mg/L, median value 4 mg/L). 

These springs and streams drain volcanic rocks, 

sandstone-shale, and limestone. Eight samples of snow 

collected in Valles Caldera in 1974 contained 0.05 to 

0.70 mg/L Cl (Trainer, 1978, table 10). This small suite 

of samples is not representative of long-term 

conditions because the samples probably represent 

only two or three storms; thus, the large suite of 144 

samples from springs and streams is more 

representative of atmosphere-derived chloride.

IU

a

2

O

o

W 5 OT °

DC

LLJ

CL

U>

5

< 0 ,- 

I I

x I x

« x X. X * X Xx XX

x x x

x x

9 m

** * * *

 j -^w.-*-* -f i ^- _!Ti-«_» . 

T " I

g 1963 1964 1965 I 1966 1967

z 10 1 

Q" 

<

0

... * ' X X

O

EQ

i *

X X X

X xx xx 

x x x x x

x x x * x x x < _

X .

 _ _ x 

A |A A A |A A A! AA|A AAA A I A A* A AA

1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982

0

01 C

.ORIDE MOLAR

O

o 1

Q

EXPLANATION

---- APPROXIMATE TREND OF CHLORIDE LOAD DURING BASE RUNOFF 

 CHLORIDE LOAD IN BASE RUNOFF SAMPLES 

J OUTLIER VALUE ABOVE LIMITS OF GRAPH PLOT

x SODIUM CHLORIDE MOLAR RATIO OF IONIC CONCENTRATIONS : 

Sodium chloride 

Sodium

A APPROXIMATE DATE OF WATER SAMPLE COLLECTED 

DURING PRODUCTION TESTING OF GEOTHERMAL 

WELLS IN VALLES CALDERA

Figure 48.-Chloride load and sodium chloride molar ratio at the Jemez River below East Fork, 

near Jemez Springs for 1963-67 and 1971-82.

104
The rather wide range in concentration in the 

suite of 144 samples is attributed to a particular aspect 

of the chloride cycle in ground water in this region. 

Chloride is a conservative constituent when dissolved 

in water that is, it is carried advectively in moving 

water, is not precipitated chemically, and is not 

absorbed on grain surfaces in host materials. However, 

there is a short-lived exception to this generalization. In 

a semiarid region much of the precipitation that 

infiltrates land surface is promptly removed by 

evaporation, and dissolved constituents concentrate in 

the soil. The constituents are then available for 

mobilization and removal by shallow unsaturated flow 

and surface runoff during the next storm. The larger 

concentrations of Cl in the dilute water are attributed to 

this mechanism.

The Na load would be expected to be larger than 

the Cl load at the gaging station Jemez River below 

East Fork as a result of Na being released by 

weathering of minerals, particularly feldspars in the 

volcanic rocks. If all Cl in streamflow is assumed to 

have come from atmospheric precipitation, then the 

ratio (Na Cl)/Na (concentrations in equivalent weights) 

expresses the "excess" Na that was derived from 

weathering. Where there is little excess Na the ratio 

approaches zero; where excess Na is larger, the ratio is 

significantly greater than zero and can approach one. 

Ratios of approximately 0.7 to 0.8 are common in the 

local dilute water thought to contain no geothermal 

component (see plot of 1963-67 data in fig. 48). 

Concentrations of Na and Cl (in equivalent weights) in 

geothermal reservoir fluids are approximately equal 

(figs. 15 and 23); consequently the ratio (Na Cl)/Na of 

geothermal fluid is close to zero and in some samples 

may be a small negative number. The addition of 

geothermal fluid to the dilute stream water, therefore, 

will result in a reduction of the (Na Cl)/Na ratio of the 

mixed stream water. Because Na and Cl concentrations 

in geothermal fluids are much larger than in stream 

water, a small addition of geothermal fluid can cause an 

appreciable shift in the (Na Cl)/Na ratio.

Drilling and testing of geothermal wells in Valles 

Caldera began in 1960; four wells were drilled during 

1960-64, followed by a hiatus before more intensive 

drilling began in 1970. Several wells underwent 

lengthy production testing. Not all water produced 

could be returned to the reservoir by injection, so part 

of it was stored in ponds retained behind earthen dams. 

Because storage ponds are likely to leak over time or

may overtop their dams during storms, small volumes 

of geothermal fluid possibly entered the stream system.

The chloride-load plot for Jemez River below 

East Fork, near Jemez Springs (fig. 48) can be 

interpreted in terms of pond leakage. According to this 

interpretation, the record of Cl load for 1963-67 

represents near-normal conditions, and the (Na Cl)/Na 

ratios during this period were typically about 0.7 to 0.8. 

During the 1970's, disturbance of the natural Na Cl 

concentration in the stream became more pronounced, 

as revealed by the wider range in the (Na Cl)/Na ratios, 

from 0.3 to 0.9. Production testing was sufficiently 

frequent during the 1970's that the stream may have 

been receiving Na Cl-charged geothermal fluid more or 

less continuously throughout much of the period after 

1972 to the early 1980's.

Determining mean values of Cl loads during 

1971-82, for which few samples are available, and 

identifying any load trends during that period are even 

more difficult than for 1963-67. The dashed trend line 

through base-flow samples in figure 48 suggests a 

steadily rising trend in chloride loads during 1971-79. 

The increasing chloride loads cannot be accounted for 

by increasing runoff, but the increasing loads are 

consistent with geothermal fluids with large chloride 

concentrations entering the stream.

The three gaging stations the Jemez River near 

Jemez (08324000); Rio Guadalupe at Box Canyon, 

near Jemez (08323000); and Jemez River below East 

Fork (08321500) provide most of the data for the 

preceding discussion of interpretation of discharge and 

hydrochemical data, although short periods of data also 

are available for Redondo Creek (08319945) and 

Sulphur Creek (08319950) (fig. 47).

Data for two other types of activities also aid in 

the design of a monitoring system: periodic 

measurements of streams, wells, and springs and 

inventories of hydrologic features that include 

repeated, but generally not systematic, measurements.

Two investigations conducted periodic 

measurements at selected sites in the southwestern 

Jemez Mountains. The LANL began systematic 

observations in 1973 in support of the laboratory's hotdry-rock experiments at the Fenton Hill site (fig. 47). 

These observations were summarized by Purtymun and 

others (1974) and in a series of mostly annual reports 

(Purtymun and others, 1975-76, 1978, 1980, 1981, 

1983,1987, 1988). The data, which represent streams, 

wells, springs, and soil and vegetation, consist 

primarily of chemical analyses. In 1972-75 the USGS

105
investigated geothermal hydrology in the Jemez 

Mountains outside Valles Caldera. As part of that study 

the USGS monitored selected streams, wells, and 

springs for discharge and water quality (Trainer, 1978, 

1984).

The LANL and USGS monitoring activities 

were coordinated on their inception in 1972-73. Both 

programs used the continuous streamflow records 

provided by the USGS gaging stations, and a degree of 

overlap was planned in monitoring other sites. The 

LANL has expanded its monitoring network 

substantially since measurements began. The 

inventories of hydrologic features (Trainer, 1978; 

Shevenell and others, 1987) are useful in planning 

monitoring programs because they contain a broad 

range of background data covering much of the region 

and include a few sets of repetitive measurements that 

supplement time series of data collected as part of the 

monitoring activities.

The LANL hot-dry-rock experiment, for which 

the first test holes were drilled in 1972, has consisted 

essentially of drilling a pair of deep holes into "dry" 

crystalline rock at a site just outside the west rim of 

Valles Caldera; creating a flow path between the wells 

at depth by hydro-fracturing; connecting the wells with 

piping at land surface; and circulating water through 

this closed loop and recovering heat from the return 

water at the surface. Representative reports that 

describe the initial development and testing include 

West (1974), Pettitt (1975a, b; 1978), West and others 

(1975), and Dash and others (1983). The following 

summary is based on information by Purtymun and 

others (1974, 1975-76, 1978, 1980, 1981, 1983, 1987, 

1988).

Large volumes of waste material have been 

produced during drilling and testing of the wells at the 

Fenton Hill site: rock cuttings, drilling mud and 

cementing materials, and mineralized water recovered 

from closed-loop circulation experiments. The 

sediment-laden and mineralized water was stored 

temporarily in pits excavated at the Fenton Hill site. 

Part of the solid material in the pits was excavated and 

buried. Part of the liquid waste infiltrated the tuff 

beneath the ponds, part of it evaporated, and part was 

released down Lake Fork Canyon (fig. 47). The canyon 

floor is dry except during runoff from melting snow and 

rainstorms, and it was anticipated that the water 

released would infiltrate alluvium in the canyon or be 

diluted and removed by surface runoff. Water release 

was approved by the U.S. Forest Service.

The possibility of both planned release and 

accidental escape of liquid wastes was the stimulus for 

establishment of the LANL monitoring study. The 

liquid wastes contain two assemblages of dissolved 

constituents: (1) constituents derived from cements and 

drilling fluids largely Ca, HCO3 , and SO4 and (2) 

moderate to large concentrations of constituents typical 

of geothermal fluid in this region, such as Na, Cl, F, B, 

and Li, attributed to dissolution of crystalline rock 

during circulation and heat-transfer experiments in the 

deep wells. The principal-constituent composition of 

the mixed wastes (fig. 49) so resembles that of natural 

geothermal fluid as to suggest that short-term flow of 

dilute water through artificial fractures in hot, 

impermeable, unweathered granitic rock can form a 

suite of dissolved constituents superficially similar to 

that produced by long-term "cooking" within the Valles 

geothermal reservoir. Summaries by Purtymun and 

others (1976, 1980a, b, 1983, 1987) show that release 

of ponded water began as early as 1975; soluble 

compounds of Cl and F were detected in soil as far as 

1,000 ft from the site down Lake Fork Canyon by 1978 

(fig. 47). Maximum concentrations of dissolved 

constituents in the discharged waste in 1979 include Cl, 

745 mg/L; F, 7.3 mg/L; As, 0.49 mg/L; B, 63 mg/L; Cd, 

0.014 mg/L; Li, 20 mg/L; and dissolved solids, 4,860 

mg/L. In 1982 high concentrations of several trace 

constituents were detected in soil, roots, and foliage 

within several hundred meters downcanyon from the 

waste ponds; no effect of the discharge was detected in 

streams or springs farther downcanyon. Nonetheless, 

the volumes of water released are substantial 1.02 

million gal in 1981 and 0.6 million gal in 1982.

SUMMARY

The Jemez Mountains in north-central New 

Mexico contain a hot-water geothermal system that 

was explored between 1970 and 1982 as a source of 

geothermal energy. This report summarizes the 

geothermal system and presents and discusses results 

of a 1972-75 USGS study. The report discusses the 

geothermal hydrology of a large central caldera known 

as the Valles Caldera, which contains the principal 

geothermal reservoir, and the southwest Jemez 

Mountains, which receive geothermal discharge from 

the reservoir. The Valles geothermal system and 

reservoir are located in the central and western parts of 

the caldera.

106
Rio Guadalupe

above Jemez River,

9-07-73

(site 20)

Jemez River

above East Fork,-

11-14-74

(site 6)

Jemez River near

Jemez, 11-14-74

(site 21)

Jemez River at

Highway 4, near

San Ysidro,

1-29-74

(site 22)

Jemez Riverabove Rio Guadalupe,

9-07-73 PERCENTAGE OF TOTAL IONS, 

(site 15) )N MILLIEQUIVALENTS PER LITER

Mean of 60 

analyses, 1981

Mean of 5 

analyses, 1978

Mean of 5 

analyses, 1983

Mean of 14 

analyses, 1982

EXPLANATION

+ JEMEZ RIVER OR RIO GUADALUPE BASINS 

(site numbers refer to figure 47)

 WASTEWATER FROM FENTON HILL 

DRILLING SITES

CHEMICAL CONSTITUENTS

SO,, + Cl Sulfate + chloride

Ca + Mg Calcium + magnesium

Na + K Sodium + potassium

CO, + HCO, Carbonate + bicarbonate

Figure 49.--Relation of major-ion composition in water samples from the Jemez River 

and Rio Guadalupe Basins and wastewater from Fenton Hill drilling sites 

(data from Trainer, 1978; and Purtymun and others, 1980a,b, 1983, and 

1987). Surface-water sampling sites shown in figure 47.

The Jemez Mountains are a complex assemblage 

of Tertiary and Quaternary volcanic rocks that overlie 

Tertiary, Mesozoic, and Paleozoic sedimentary rocks 

and Precambrian crystalline rocks. The mountains 

form an oval topographic mound that occupies about 

1,500 mi2 and contains the Valles Caldera. The 

topographic rim of the caldera is approximately 

circular and about 14 to 18 mi in diameter. The ringfracture zone, along which the caldera floor has 

collapsed, is about 8-10 mi in diameter. A resurgent 

dome known as Redondo Peak occupies about onefourth of the caldera.

The topographic rim of Valles Caldera forms a 

near-circular drainage basin with a surface outlet on the 

southwest. Two principal streams San Antonio Creek 

and the East Fork Jemez River drain the caldera and 

join near the southwest rim to form the Jemez River, 

which flows down Canon de San Diego, then east to 

join the Rio Grande. The caldera contains both thermal 

and nonthermal ground water, and both types of ground 

water discharge to the southwest as ground-water

underflow beneath Canon de San Diego, which follows 

the trace of the Jemez Fault Zone. In other areas outside 

the rim, ground water flows radially away from the 

caldera.

Several distinct types of nonthermal and thermal 

ground water are recognized in the Jemez Mountains. 

Nonthermal ground water in Valles Caldera occurs in 

diverse perched aquifers and deeper valley-fill aquifers. 

Recharge occurs principally by infiltration of 

precipitation on surrounding mountain slopes, alluvial 

fans, and benches. Natural discharge occurs as spring 

flow, seepage to the major streams draining the valleys, 

and as downward leakage to the deeper geothermal 

reservoir.

The near-surface thermal water in the caldera is 

grouped into two types based on geochemistry and 

geohydrology: thermal meteoric water and acid sulfate 

water. Thermal meteoric water, heated by the high 

conductive heat flux in that area, discharges from 

fractures in rhyolite and from contacts between rhyolite 

and underlying sedimentary rocks in the ring-fracture

107
zone of the western and southwestern parts of the 

caldera. Geochemical data indicate that thermal water 

circulates within the upper 1,500 ft of the caldera moat 

and generally entered the ground-water system more 

than 50 years prior to its discharge at the springs.

Acid sulfate water is characterized by low pH 

(0.6 to 5) and by large concentrations of sulfate (greater 

than 1,000 mg/L). Acid sulfate water issues from 

fractures and faults on the western slope of the 

resurgent dome, principally in the Sulphur Springs 

area. Sulphur Springs is the most active zone of surface 

thermal manifestations in the caldera and contains 

thermal and nonthermal springs, mud pots, and 

fumaroles. These thermal features are manifestations 

of an underlying vapor-dominated zone.

High rates of near-surface heat flow and high 

subsurface temperatures characterize the western half 

of Valles Caldera and adjacent parts of Jemez Plateau 

to the west. Heat flow increases markedly as the rim of 

the caldera is approached from the west, and 

temperature gradients within the caldera are markedly 

greater than those outside the caldera rim.

The main geomermal reservoir is recharged by 

meteorically derived water. The water moves 

downward from the overlying aquifers in the caldera 

fill and laterally recharges the geothermal reservoir in 

intracaldera tuffs and precaldera rocks at depths of 

6,500 ft or more and at temperatures reaching 330 °C. 

The heated geothermal water subsequently rises 

convectively to depths of about 2,000 ft or less. A 

vapor-dominated zone (or zones) containing steam, 

CO2, and other gases has formed above parts of the 

liquid-dominated zone, most notably in the Sulphur 

Springs area. The heated water of the geothermal 

system flows out the caldera to the west and southwest 

under the Jemez Plateau and along the Jemez Fault 

Zone and in the semipermeable Paleozoic rocks that 

border the fault zone.

Two important subsystems have been identified 

within the larger geothermal system: the Redondo 

Creek subsystem under the central part of the resurgent 

dome and the Sulphur Creek subsystem under the 

northwestern part of the dome. Permeability of the 

Redondo Creek subsystem is controlled by both 

stratigraphic and fault-related structures. 

Stratigraphically controlled permeability occurs in 

tuffaceous sandstones and nonwelded tuff units spaced 

throughout the Bandelier Tuff. At least two main zones 

of permeability exist: a deeper zone about 500 ft thick 

at the contact between the Bandelier Tuff and the

underlying Paliza Canyon Formation and a generally 

more productive upper zone within the Bandelier Tuff. 

Most of the permeability is produced by the high-angle, 

normal faults and associated fractures that form the 

Redondo Creek Graben.

The Sulphur Springs subsystem is not as well 

defined as the Redondo Creek subsystem. Faults and 

related fractures control the flow of thermal fluids in 

the subsystem, which is bounded by grabenlike faults. 

An upper vapor-dominated zone is separated from the 

liquid-dominated zone by about 800 ft of sealed 

caldera-fill rock. Chemical and thermal evidence 

indicates that the Sulphur Springs subsystem may be 

isolated from the Redondo Creek subsystem, and each 

may have its own zone of upflow and lateral discharge.

Estimates of the area and thickness of the 

geothermal reservoir vary. The area of the entire 

reservoir is estimated to be between 12 and 15 mi2 by 

recent investigators, and its western limit is thought to 

be at the ring-fracture zone of the caldera. Most 

investigators place the top of the reservoir at the bottom 

of a small-permeability "caprock" that is about 2,000 to 

3,000 ft below land surface. The bottom of the reservoir 

is more difficult to define. Estimated thickness of the 

bottom of the reservoir ranges from 2,000 to 6,000 ft. 

Reservoir temperatures measured in wells ranged from 

225 °C just below the caprock to about 330 °C in 

deeper wells. Pressures measured in exploration wells 

in the Redondo Creek area ranged from 450 to 1,850 

lb/in2 .

The geochemistry of water in the geothermal 

reservoir is typical of volcanic geothermal water. The 

reservoir contains a near-neutral, chloride-type water 

containing about 7,000 mg/L dissolved solids and 

anomalously large concentrations of As, B, Br, Cs, Li, 

Rb, and other trace elements. Thermal spring water in 

the caldera has no geochemical characteristics similar 

to those of the geothermal reservoir fluids sampled 

from wells.

Oxygen-18 and deuterium concentrations of 

geothermal reservoir fluid support a meteoric origin. 

The geothermal fluid is enriched in I8O relative to the 

meteoric-water line for the Jernez Mountains region, 

and the amount of enrichment is typical of that 

measured in other geothermal systems.

The entire r -\ldera depression and surrounding 

rim of highlands are thought to serve as the recharge 

area; the moat valleys in north and east areas may be 

the principal recharge zones of the reservoir. 

Downward flow along fault zones and fractures
probably is the primary mechanism of recharge. The 

recharge probably flows downward around the outer 

edges of the reservoir or along the caldera ring 

fractures, enters the reservoir at depth where it is 

heated, then rises convectively within the reservoir.

Pressure measurements in wells in the Redondo 

Creek area and in Baca wells 7 and 8 define a consistent 

gradient within the reservoir that corresponds to a 

hydrostatic gradient at approximately 260 °C. The 

gradient extrapolates to atmospheric pressure at 1,100 

ft below a land-surface altitude of 9,000 ft in the 

Redondo Creek graben but about 1,500 ft above the 

level of thermal discharges at Jemez Springs. The 

pressure gradient indicates upward flow in regions 

where temperatures exceed 260 °C. Flow conduits 

between the geothermal reservoir and distant areas of 

thermal-water discharge at low altitude allow the 

reservoir to effectively be underpressured so boiling 

occurs at depth and a zone of steam upflow under 

vapor-static pressure conditions develops.

Subsurface escape of reservoir fluid 

southwestward from beneath Valles Caldera has 

formed a discharge plume of reservoir water mixed 

with dilute ground water near and beneath Canon de 

San Diego, which extends downcanyon in conduits at 

least as far as Soda Dam and Jemez Springs and brings 

mineral water to these areas.

An estimated 25-50 percent of the discharge 

flows laterally toward Canon de San Diego and is 

channeled along vertical conduits in the Jemez Fault 

Zone where the fault zone intersects the caldera. The 

hot springs in Canon de San Diego at Soda Dam and 

Jemez Springs are derivatives of subsurface outflow 

from the geothermal reservoir. The fault zone 

transports a large portion of the flow, and the remainder 

is assumed to be distributed on either side of the fault 

zone and contained primarily in horizontal, 

semipermeable sedimentary strata. The lateral extent of 

discharge from the geothermal reservoir has not been 

fully defined.

The mineral water from springs at Jemez Springs 

and Soda Dam has a Na Cl composition and large 

concentrations of Ca and HCO3 . The Li/Na, Li/Cl, and 

B/C1 ratios of the mineral water are in ranges typical of 

volcanic waters. Differences in temperature and in 

chemical composition and concentration exist between 

the mineral water at Jemez Springs and Soda Dam, 

which indicate flow along different paths and probably 

differences related to the nature of the dilute water and 

the location of mixing.

Reservoir fluid from the Sulphur Creek 

subsystem is the likely geothermal parent of mineral 

water beneath the Jemez Plateau west of the caldera, 

based on chemical and stable-isotope data from 

mineral-water samples collected beneath the plateau. 

The course the reservoir fluid takes when leaving the 

plateau has not been established; flow southeastward to 

Canon de San Diego is possible but needs further study.

Geophysical evidence indicates a gap in the 

intrusive rocks of the caldera ring-fracture zone near 

the site where San Antonio Creek flows out the caldera. 

The proximity of this site to the Jemez Fault Zone 

provides a general explanation for escape of reservoir 

fluid in the subsurface down Canon de San Diego.

At least two principal or regional aquifers are in 

the southern Jemez Mountains: the geothermal 

reservoir(s) in Valles Caldera and associated discharge 

conduits, and the rift-fill sediments at the southern and 

southwestern edges of the study area. South and 

southwest of the caldera rim mineral-water conduits 

are near the base of the sedimentary section, and in this 

form, the geothermal aquifer probably extends 

southward as far as Jemez Pueblo. Near there, 

subsurface mineral water merges with the regional 

aquifer in fill deposits of the Rio Grande Rift. The 

dilute-water aquifer in the east slope of the Sierra 

Nacimiento west of Jemez Pueblo probably merges to 

the east with the regional aquifer in fill deposits of the 

Rio Grande Rift. It is generally assumed that no single 

reservoir fluid and no single dilute fluid are parents of 

all derivative mineral water outside the caldera.

All sites of outflowing mineral water appear to 

be in the western and southwestern parts of the caldera 

rim. No evidence of escaping geothermal fluid has been 

found on the northwest or northern flanks of the Jemez 

Mountains, and the stable-isotope composition of 

ground water rules out leakage to the east.

Mineral water in the southern Sierra Nacimiento 

and near San Ysidro is derived from a separate lowtemperature geothermal system along the Nacimiento 

Fault Zone rather than from a Valles Caldera parent. 

The Nacimiento water comes from or through 

limestone and gypsum-bearing rocks and is 

characterized by large concentrations of HCO3 , SO4, 

Cl, Li, and B. The water mixes near San Ysidro with 

water moving down Canon de San Diego. Springs near 

San Ysidro represent a series of intermediate mixtures.

109
Total geothermal discharge from the caldera 

consists of three components: streamflow, ground 

water in alluvium beneath the stream channel and 

canyon floor, and conduit flow in bedrock. Total 

discharge from the geothermal reservoir is difficult to 

estimate; all estimates, however, suggest a small 

discharge of geothermal fluid from the caldera. About 

1.0 ft3/s of caldera-derived geothermal fluid is 

estimated to be carried by the Jemez River between 

Jemez Pueblo and San Ysidro, and about 0.4 ft3/s is 

estimated to be carried as underflow in the same reach. 

The estimates do not include any flow in subsurface 

conduits. Estimates of total discharge from the 

geothermal reservoir to the Rio Grande at its 

confluence with the Jemez River, as measured by 

increases in chemical load, range from 2.0 to 3.6 ft3/s 

and average 2.8 ft3/s, but these estimates may include 

discharge from the Sierra Nacimiento.

The conceptual model of the Valles geothermal 

system in this study involves a liquid-dominated 

reservoir with a parasitic vapor-dominated zone. The 

system contains an upflow zone and a region of twophase (boiling) conditions at which liquid and steam 

phases separate; steam rises through a vapordominated zone to discharge at high altitudes, and 

liquid flows laterally to discharge as springs and river 

seepage at low altitudes. The basic conceptual model of 

the Valles geothermal system used to develop any 

future numerical models needs to include the above 

aspects of the system and account for complications 

related to heterogeneity in thermodynamic and 

hydrologic conditions within the reservoir, such as 

separate productive zones at different depths in the 

Redondo Creek Graben area and hydrologic separation 

between the Redondo Creek and the Sulphur Creek 

areas, which may have separate recharge/discharge 

subsystems.

Various numerical models of the geothermal 

system in Valles Caldera and surrounding region have 

been developed primarily to assess reservoir 

productivity and longevity and potential effects of 

development on thermal-water discharge in the Jemez 

River. Existing numerical models of the system range 

in complexity from one-dimensional, single-phase 

fluid-flow models to three-dimensional, multiphasefluid and heat-flow models. The differences in 

modeling approach resulted in a range of 6.3 to 1,234 

gal/min for calculated depletion of thermal-water 

discharge to the Jemez River from 30-year simulations 

of geothermal development at the 50-megawatt level.

Further, the models simulating possible production and 

injection scenarios over a 30-year period give 

considerably different results of predicted reservoir 

drawdown and reservoir productivity over time. A 

period of actual geothermal development, in which the 

system is stressed and the resulting hydrologic changes 

are measured, is missing. Existing models must be 

considered preliminary and cannot provide accurate 

answers to questions involving long-term changes to 

the geothermal system.

The elements necessary to successfully model 

the Valles hydrothermal system include (1) threedimensional descriptions of fluid and heat flow that can 

treat both lateral and vertical heterogeneities; (2) a 

multiphase thermodynamic and fluid-flow formulation; 

(3) hydrologic continuity between the geothermal 

reservoir and the discharge plume of thermal water in 

areas inside and outside the caldera; (4) capability to 

allow for variable input rates of high-enthalpy fluid into 

the geothermal reservoir; and (5) capability to treat 

different production/injection scenarios as affected by 

changes in steam fractions in regions around 

production wells. An existing model has these 

capabilities, yet is simple enough that it can be used to 

test combinations of different parameters or to examine 

the importance of two-phase effects and vertical 

variations in reservoir properties and fluid 

(thermodynamic) states in modeling the reservoir 

response to development.

The concentrations of CC>2 in the reservoir fluid 

have not been adequately delineated from existing 

sampling and wellhead measurements, but based on 

what is known, the CC>2 concentrations appear to be 

sufficient to markedly extend the depth over which 

two-phase conditions occur naturally and possibly to 

influence reservoir drawdown during development. 

Existing models do not account for the presence of C02 

in the reservoir fluid. This matter requires further study 

to allow for more accurate simulation of reservoir 

performance and longevity during development.

Development of geothermal energy in Valles 

Caldera would probably change hydrochemical 

discharge from the southwestern Jemez Mountains. 

Quantifying such changes, which could be 

accomplished by systematic monitoring, would be 

valuable in better understanding the geothermal system 

and in testing, refining, and calibrating numerical 

models of the system.

110
SELECTED REFERENCES

Abeyta, C.G., and Delaney, B.M., 1986, Annotated

bibliography of the hydrology, geology, and geothermal 

research of the Jemez Mountains and vicinity, northcentral New Mexico: U.S. Geological Survey OpenFile Report 85-83, 155 p.

 1990, Hydrologic data for the Jemez Mountains, 

New Mexico: U.S. Geological Survey Open-File 

Report 90-176, 51 p.

Aldrich, M.J., Jr., 1986, Tectonics of the Jemez lineament in 

the Jemez Mountains and Rio Grande Rift: Journal of 

Geophysical Research, v. 91, no. B2, p. 1753-1762.

American Ground Water Consultants, Inc., 1980a,

Hydrogeology of the Hot Dry Rock site at Fenton Hill, 

Sandoval County, New Mexico: Report to Los Alamos 

Scientific Laboratory.

 1980b, Results of ground-water model studies at 

Fenton Hill, Sandoval County, New Mexico: Report to 

Los Alamos Scientific Laboratory.

Anderholm, S.K., 1988, Ground-water geochemistry of the 

Albuquerque-Belen Basin, central New Mexico: U.S. 

Geological Survey Water-Resources Investigations 

Report 86-4094,110 p.

Bailey, R.A., 1961, Hot spring and solfataric areas in the 

Valles Caldera, Jemez Mountains, New Mexico: U.S. 

Geological Survey Open-File Map, scale 1:62,500.

Balleau, W.P., 1980, Geothermal hydrology at Jemez 

Mountains Ion balance and flow depletion: 

Albuquerque, N. Mex., Bureau of Indian Affairs 

unpublished report, 16 p.

Becker, N.M., Purtymun, W.D., and Ballance, W.C., 1981, 

Aquifer evaluation at Fenton Hill, October and 

November 1980: Los Alamos National Laboratory 

Report LA-8964-MS.

Bodvarsson, G.S., Yonder Haar, S., Wilt, M.J., and Tsang, 

C.F., 1982, Preliminary studies of the reservoir capacity 

and generating potential of the Baca geothermal field, 

New Mexico: Water Resources Research, v. 18, 

p. 1713-1723.

Charles, R.W., Vidale Buden, R.J., and Goff, Fraser, 1986, 

An interpretation of the alteration assemblages at 

Sulphur Springs, Valles Caldera, New Mexico: Journal 

of Geophysical Research, v. 91, no. B2, p. 1887-1898.

Clark, J.D., 1929, The saline springs of the Rio Salado: 

Albuquerque, University of New Mexico Bulletin, 

Chemistry Series, v. 1, no. 3,29 p.

Clark, S.P., Jr., ed., 1966, Handbook of physical constants 

(rev. ed.): Geological Society of America Memoir 97, 

587 p.

Conover, C.S., Theis, C.V., and Griggs, R.L., 1963, Geology 

and hydrology of Valle Grande and Valle Toledo, 

Sandoval County, New Mexico: U.S. Geological 

Survey Water-Supply Paper 1619-Y, 37 p.

Craigg, S.D., 1984, Hydrologic data on the Pueblos of 

Jemez, Zia, and Santa Ana, Sandoval County, New 

Mexico: U.S. Geological Survey Open-File Report 84- 

460, 37 p.

 1992, Water resources on the Pueblos of Jemez, Zia, 

and Santa Ana, Sandoval County, New Mexico: U.S. 

Geological Survey Water-Resources Investigations 

Report 89-4091,122 p.

Dash, Z.V., Murphy, H.D., Aamodt, R.L., Aguilar, R.G., 

Brown, D.W., Counce, D.A., Fisher, H.N., Grigsby, 

C.O., Keppler, H., Laughlin, A.W., Potter, R.M., Tesfer, 

J.W., Trujillo, P.E., Jr., and Zyvoloski, G., 1983, Hot dry 

rock geothermal reservoir testing, 1978 to 1980: 

Journal Volcanology and Geothermal Research, v. 15, 

p. 59-99.

Delany, J.M., and Truesdell, A.H., 1982, Geochemical 

indicators of reservoir conditions, in Goldstein, N.E., 

Holman, W.R., and Molloy, M.W., eds., Final report of 

the Department of Energy reservoir definition review 

team for the Baca geothermal demonstration project: 

University of California, Lawrence Berkeley 

Laboratory Report LBL-14132, p. 18-21.

Doell, R.R., Dalrymple, G.B., Smith, R.L., and Bailey, R.A., 

1968, Paleomagnetism, potassium-argon ages, and 

geology of rhyolites and associated rocks of the Valles 

Caldera, New Mexico, in Coats, R.R., and others, eds., 

Studies in volcanology: Geological Society of America 

Memoir 116, p. 211-248.

Dondanville, R.F., 1971, The hydrothermal geology of the 

Valles Caldera, Jemez Mountains, New Mexico: 

Consultant's report to Union Oil Company of 

California, Santa Rosa, Calif, (released 1978), 36 p.

 1978, Geologic characteristics of the Valles Caldera 

geothermal system, New Mexico: Geothermal 

Resources Council Transactions, v. 2, sec. 1, p. 157- 

160.

Faust, C.R., Mercer, J.W, and Thomas, S.D., 1983,

Quantitative analysis of geothermal development in the 

Jemez Mountains, final report: Contract 

MOOC14203411, Bureau of Indian Affairs, 

Albuquerque, N. Mex., 87 p. and 5 app.

Faust, C.R., Mercer, J.W., Thomas, S.D., and Balleau, W.P., 

1984, Quantitative analysis of existing conditions and 

production strategies for the Baca geothermal system, 

New Mexico: Water Resources Research, v. 20, no. 5, 

p. 601-618.

Galusha, Ted, and Blick, J.C., 1971, Stratigraphy of the 

Santa Fe Group, New Mexico: American Museum of 

Natural History Bulletin, v. 144, article 1, 127 p.

Gardner, J.N., Goff, Fraser, Garcia, Sammy, and Hagan, 

R.C., 1986, Stratigraphic relations and lithologic 

variations in the Jemez volcanic field, New Mexico: 

Journal of Geophysical Research, v. 91, no. B2, 

p. 1763-1778.

111
Garg, Sabodh, and Riney, T.D., 1982, Reservoir definition 

and conceptual model, in Goldstein, N.E., Holman, 

W.R., and Molloy, M.W., eds., Final report of the 

Department of Energy reservoir definition review team 

for the Baca geothermal demonstration project: 

University of California, Lawrence Berkeley 

Laboratory Report LBL-14132, p. 31-36.

Goff, Fraser, Gardner, J.N., Hulen, J.B., Nielson, D.L., 

Charles, Robert, WoldeGabriel, Giday, Vuataz, F.D., 

Musgrave, J.A., Shevenell, Lisa, and Kennedy, B.M., 

1992, The Valles caldera hydrothermal system, past and 

present, New Mexico, USA: Springer-Verlag, Scientific 

Drilling, v. 3, p. 181-204.

Goff, Fraser, Gardner, Jamie, Vidale, Rosemary, and

Charles, Robert, 1985, Geochemistry and isotopes of 

fluids from Sulphur Springs, Valles Caldera, New 

Mexico: Journal of Volcanological and Geothermal 

Research, v. 23, p. 273-297.

Goff, Fraser, and Grigsby, C.O., 1982, Valles Caldera

geothermal systems, New Mexico, U.S.A.: Journal of 

Hydrology, v. 56, p. 119-136.

Goff, F.E., Grigsby, C.O., Trujillo, P.E., Jr., Counce, Dale, 

and Kron, Andrea, 1981, Geology, water geochemistry, 

and geothermal potential of the Jemez Springs area, 

Canon de San Diego, New Mexico: Journal of 

Volcanology and Geothermal Research, v. 10, p. 227- 

244.

Goff, F.E., and Kron, Andrea, 1980, In-progress geologic 

map of Canon de San Diego, Jemez Springs, New 

Mexico, and lithologic log of Jemez Springs 

geothermal well: Los Alamos Scientific Laboratory 

Informal Map LA-8276-MAP, one sheet, scale 

1:12,000.

Goff, F.E., McCormick, Tamsin, Trujillo, P.E., Jr., Counce, 

Dale, and Grigsby, C.O., 1982, Geochemical data for 95 

thermal and nonthermal waters of the Valles 

caldera Southern Jemez Mountains region New 

Mexico: University of California, Los Alamos National 

Laboratory Report LA-9367-OBES, 51 p.

Goff, Fraser, Rowley, John, Gardner, J.N., Hawkins, Ward, 

Goff, Sue, Charles, Robert, Wachs, Daniel, Maasseu, 

Larry, and Heiken, Grant, 1986, Initial results from VC1, first Continental Scientific Drilling Program core 

hole in Valles caldera, New Mexico: Journal of 

Geophysical Research, v. 91, no. B2, p. 1742-1752.

Goff, F.E., and Sayer, Suzanne, 1980, A geothermal 

investigation of spring and well waters of the Los 

Alamos region, New Mexico: Los Alamos National 

Laboratory Informal Report LA-8326-MS, 21 p.

Goff, Fraser, and Shevenell, Lisa, 1987, Travertine deposits 

of Soda Dam, New Mexico, and their implications for 

the age and evolution of the Valles caldera 

hydrothermal system: Geological Society of America 

Bulletin, v. 99, p. 292-302.

Goff, Fraser, Shevenell, Lisa, Gardner, J.N., Vuataz, F.D., 

and Grigsby, C.O., 1988, The hydrothermal outflow 

plume of the Valles Caldera, New Mexico, and a 

comparison with other outflow plumes: Journal of 

Geophysical Research, v. 93, no. B6, p. 6041-6058.

Goldstein, N.E., Holman, W.R., and Molloy, M.W., eds., 

1982, Final report of the Department of Energy 

reservoir definition review team for the Baca 

geothermal demonstration project: University of 

California, Lawrence Berkeley Laboratory LBL-14132, 

51 p.

Grant, M.A., 1979, Interpretation of downhole 

measurements at Baca: Proceedings of the 8th 

Geothermal Workshop, Stanford University, Palo Alto, 

Calif., p. 261-267.

Grant, M.A., Garg, S.K., and Riney, T.D., 1984,

Interpretation of downhole data and development of a 

conceptual model for the Redondo Creek area of the 

Baca geothermal field: Water Resources Research, 

v.20,no. 10, p. 1401-1416.

Griggs, R.L., 1964, Geology and ground-water resources of 

the Los Alamos area, New Mexico, with a section on 

Quality of water, by J.D. Hem: U.S. Geological Survey 

Water-Supply Paper 1753, 107 p.

Grigsby, C.O., Goff, Fraser, Trujillo, P.E., and Counce, D.A., 

1984, Geochemical behavior of a hot dry rock 

geothermal reservoir: Socorro, New Mexico Geological 

Society Field Conference Guidebook, 35th Field 

Conference, p. 265-270.

Hartz, J.D., 1976, Geothermal reservoir evaluation of the 

Redondo Creek area, Sandoval County, New Mexico: 

Internal report, Union Oil Company, Santa Rosa, Calif.

Heiken, Grant, Goff, Fraser, Stix, John, Tamanyu, Shiro, 

Shafiqullah, Muhammad, Garcia, Sammy, and Hagan, 

Roland, 1986, Intracaldera volcanic activity, Toledo 

Caldera and embayment, Jemez Mountains, New 

Mexico: Journal of Geophysical Research, v. 91, no. 

B2,p. 1799-1815.

Hem, J.D., 1970, Study and interpretation of the chemical 

characteristics of natural water (2d ed.): U.S. 

Geological Survey Water-Supply Paper 1473, 363 p.

Hulen, J.B., 1982, Structure, stratigraphy, and permeability 

in the Redondo Creek project area, in Goldstein, N.E., 

Holman, W.R., and Molloy, M.W., eds., Final report of 

the Department of Energy reservoir definition review 

team for the Baca geothermal demonstration project: 

University of California, Lawrence Berkeley 

Laboratory Report LBL-14132, p. 7-14.

Hulen, J.B., and Nielson, D.L., 1986, Hydrothermal 

alteration in the Baca geothermal system, Redondo 

dome, Valles Caldera, New Mexico: Journal of 

Geophysical Research, v. 91, no. B2, p. 1867-1886.

Ingebritsen, S.E., and Sorey, M.L., 1985, A quantitative 

analysis of the Lassen hydrothermal system, north112
central California: Water Resources Research, v. 21, 

no. 6, p. 853-868. 

Jiracek, G.R., 1974, Geophysical studies in the Jemez

Mountains region, New Mexico: Socorro, New Mexico 

Geological Society Guidebook, 25th Field Conference, 

p. 137-144.

 1975, Deep electrical resistivity investigations

coupled with dry geothermal reservoir experiments in 

New Mexico: Albuquerque, University of New Mexico 

Technical Progress Report to U.S. National Science 

Foundation/RANN, Contract NSF GI-42835,47 p.

Jiracek, G.R., Smith, C., and Dorn, G.A., 1975, Deep

geothermal exploration in New Mexico using electrical 

resistivity: Second United Nations Symposium on the 

Development and Use of Geothermal Resources, 

Proceedings, v. 2, p. 1095-1102.

John, E.G., Enyart, E.A., and Purtymun, W.D., 1967,

Records of wells, test holes, springs, and surface-water 

stations in the Los Alamos area, New Mexico: U.S. 

Geological Survey Open-File Report, 129 p.

Journal of Geophysical Research, 1986, including Special 

Section Recent research in the Valles Caldera: 

American Geophysical Union, v. 91, no. B2, p. 1741- 

2218.

 1988, including Special Section Research in the 

Valles Caldera: American Geophysical Union, v. 93, 

no. B6, p. 5997-6668.

Kelley, V.C., 1969, Albuquerque-^-Its mountains, valley, 

water, and volcanoes: Socorro, New Mexico Bureau of 

Mines and Mineral Resources, Scenic Trips to the 

Geologic Past, no. 9, 101 p.

Kelly, Clyde, and Anspach, E.V., 1913, A preliminary study 

of the waters of the Jemez Plateau, New Mexico: 

Albuquerque, University of New Mexico Bulletin, 

Chemistry Series, v. 1, no. 1,43 p.

Kelly, T.E., and Reinert, Scott, 1996, Arsenic stratification in 

the Santa Fe Formation, Bernalillo, New Mexico: New 

Mexico Geological Society Guidebook, 47th Annual 

Field Conference, Jemez Mountains Region, p. 481- 

484.

Kunkel, K.E., 1984, Temperature and precipitation

summaries for selected New Mexico locations: Las 

Cruces, Office of the State Climatologist, New Mexico 

Department of Agriculture, 190 p.

Lambert, S., and Epstein, S., 1980, Stable isotope

investigation of an active geothermal system in Valles 

Caldera, New Mexico: Journal of Volcanology and 

Geothermal Research, v. 8, p. 111-129.

Mariner, R.H., Presser, T.S., and Evans, W.C., 1977, 

Chemical, isotope, and gas composition of selected 

thermal springs in Arizona, New Mexico, and Utah: 

U.S. Geological Survey Open-File Report 77-654,56 p.

New Mexico Environment Department, 1991, Special waterquality survey of the Rio Grande from Angostura 

diversion works to 1-25 in Sandoval and Bernalillo

Counties, New Mexico, June 18-September 18,1991,/n 

Intensive water-quality stream surveys and lake waterquality assessment surveys: New Mexico Environment 

Department Report NMED/SWQ-92/2, p. 118-149.

New Mexico State Engineer Office, 1980, Report and

recommendation of Hearing Examiner in the matter of 

application of Marcel and Thomas Abousleman 

number 02541B and RG-32624 for an alternate point of 

diversion and new place and purpose of use from 

surface water to geothermal water and to appropriate 

the underground waters of the State of New Mexico, 

Bernalillo, N. Mex., April 10-11, 1980: 9 p.

Nielson, D.L., and Hulen, J.B., 1984, Internal geology and 

evolution of the Redondo dome, Valles Caldera, New 

Mexico: Journal of Geophysical Research, v. 89, no. 

BIO, p. 8695-8711.

Pearson, Chris, and Goff, Fraser, 1981, A Schlumberger 

resistivity study of the Jemez Springs region of 

northwestern New Mexico: Geothermal Resources 

Council Transactions, v. 5, p. 119-122.

Pettitt, R.A., 1975a, Planning, drilling, and logging of 

Geothermal Test Hole GT-2, Phase I: Los Alamos 

Scientific Laboratory Progress Report LA-5819-PR, 

42 p.

 1975b, Testing, drilling, and logging of Geothermal 

Test Hole GT-2, Phase II: Los Alamos Scientific 

Laboratory Progress Report LA-5897-PR, 21 p. 

-1978, Testing, planning, and redrilling of

Geothermal Test Hole GT-2, Phases IV and V: Los 

Alamos Scientific Laboratory Progress Report LA7586-PR,60p.

Pierce, ST., 1989, Intensive water-quality survey of the Rio 

Grande from Angostura to U.S. 85 bridge, Sandoval 

and Bernalillo Counties, New Mexico, July 25-28, 

1988: New Mexico Environmental Improvement 

Division Report EID/SWQ-8816, 51 p.

Pritchett, J.W., Rice, L.F., and Riney, T.D., 1981, Effects of 

CO2 content on geothermal systems Implications for 

Baca reservoir: Transactions of the Geothermal 

Resources Council, v. 5, p. 369-372.

Purtymun, W.D., Adams, W.H., and Owens, J.W., 1975, 

Water quality in vicinity of Fenton Hill site, 1974: Los 

Alamos Scientific Laboratory Report LA-6093, 16 p.

Purtymun, W.D., Adams, W.H., and Stoker, A.K., 1978, 

Water quality in vicinity of Fenton Hill site, 1976: Los 

Alamos Scientific Laboratory Informal Report LA7307-MS, 17 p.

Purtymun, W.D., Adams, W.H., Stoker, A.K., and West, 

F.G., 1976, Water quality in vicinity of Fenton Hill site, 

1975: Los Alamos Scientific Laboratory Informal 

Report LA-6511-MS, 21 p.

Purtymun, W.D., and Cooper, J.B., 1969, Development of 

ground-water supplies on the Pajarito Plateau, Los 

Alamos County, New Mexico: U.S. Geological Survey 

Professional Paper 650-B, p. B149-B153.

113
Purtymun, W.D., Ferenbaugh, R.W., and Adams, W.H., 

1981, Water quality in the vicinity of Fenton Hill, 1980: 

Los Alamos National Laboratory Progress Report LA9007-PR, 16 p.

Purtymun, W.D., Ferenbaugh, R.W., Becker, N.M., Adams, 

W.H., and Macs, M.N., 1983, Water quality in the 

vicinity of Fenton Hill, 1981 and 1982: Los Alamos 

National Laboratory Progress Report LA-9854-PR, 

30 p.

Purtymun, W.D., Ferenbaugh, R.W., Becker, N.M.,

Williams, M.C., and Macs, M.N., 1987, Water quality 

in the vicinity of Fenton Hill, 1983 and 1984: Los 

Alamos National Laboratory Progress Report LA10892-PR, 37 p.

Purtymun, W.D., Ferenbaugh, R.W., Stoker, A.K., and 

Adams, W.H., 1980a, Water quality in the vicinity of 

Fenton Hill, 1979: Los Alamos Scientific Laboratory 

Progress Report LA-8424-PR, 21 p.

Purtymun, W.D., Ferenbaugh, R.W., Stoker, A.K., Adams, 

W.H., and Owens, J.W., 1980b, Water quality in the 

vicinity of Fenton Hill, 1978: Los Alamos Scientific 

Laboratory Progress Report LA-8217-PR, 21 p.

Purtymun, W.D., Ferenbaugh, R.W., Williams, M.C., and 

Maes, M.N., 1988, Water quality in the vicinity of 

Fenton Hill, 1985 and 1986: Los Alamos National 

Laboratory Progress Report LA-11210-PR, 36 p.

Purtymun, W.D., and Johansen, Steven, 1974, General 

geohydrology of the Pajarito Plateau: New Mexico 

Geological Society Guidebook, 25th Field Conference, 

p. 347-349.

Purtymun, W.D., Stoker, A.K., Adams, W.H., and Owens, 

J.W., 1978: Water quality in the vicinity of Fenton Hill 

site, 1977: Los Alamos Scientific Laboratory Progress 

Report LA-7468-PR, 16 p.

Purtymun, W.D., West, F.G., and Adams, W.H., 1974,

Preliminary study of the quality of water in the drainage 

area of the Jemez River and Rio Guadalupe: Los 

Alamos Scientific Laboratory Informal Report LA5595-MS, 26 p.

Reiter, Marshall, Edwards, C.L., Hartman, Harold, and 

Weidman, Charles, 1975, Terrestrial heat flow along the 

Rio Grande Rift, New Mexico and southern Colorado: 

Geological Society of America Bulletin, v. 86, no. 6, 

p. 811-818.

Reiter, Marshall, Shearer, Charles, and Edwards, C.L., 1978, 

Geothermal anomalies along the Rio Grande Rift, New 

Mexico: Geology, v. 6, p. 85-88.

Reiter, Marshall, Shearer, Charles, Edwards, C.L., and

Hartman, Harold, 1976, Subsurface temperature data in 

Jemez Mountains, New Mexico: Socorro, New Mexico 

Bureau of Mines and Mineral Resources Circular 151, 

16 p.

Renick, B.C., 1931, Geology and ground-water resources of 

western Sandoval County, New Mexico: U.S. 

Geological Survey Water-Supply Paper 620, 117 p.

Sass, J.H., and Morgan, Paul, 1988, Conductive heat flux in 

VC-1 and the thermal regime of Valles caldera, Jemez 

Mountains, New Mexico: Journal of Geophysical 

Research, v. 91, no. B6, p. 6027-6039.

Self, Stephen, GofT, Fraser, Gardner, J.N., Wright, J.V., and 

Kite, W.M., 1986, Explosive rhyolitic volcanism in the 

Jemez Mountains Vent locations, caldera 

development, and relation to regional structure: Journal 

of Geophysical Research, v. 91, no. B2, p. 1779-1798.

Self, Stephen, Heiken, Grant, Sykes, M.L., Wohletz, 

Kenneth, Fisher, R.V., and Dethier, D.P., 1996, Field 

excursions to the Jemez Mountains, New Mexico: 

Socorro, New Mexico Bureau of Mines and Mineral 

Resources Bulletin 134, 72 p.

Shevenell, Lisa, Goff, Fraser, Miles, Dan, Waibel, Al, and 

Swanberg, Chandler, 1988, Lithologic descriptions and 

temperature profiles of five wells in the southwestern 

Valles caldera region, New Mexico: Los Alamos 

National Laboratory Report LA-11165-OBES, 43 p.

Shevenell, Lisa, Goff, Fraser, Vuataz, F.D., Trujillo, P.E., Jr., 

Counce, D., Janick, C. J., and Evans, B., 1987, 

Hydrogeochemical data for the thermal and nonthermal 

waters and gases of the Valles Caldera Southern 

Jemez Mountains region, New Mexico: Los Alamos 

National Laboratory Report LA-10923-OBES, 100 p.

Smith, R.L., and Bailey, R.A., 1968, Resurgent cauldrons, in 

Coats, R.R., and others, eds., Studies in volcanology: 

Geological Society of America Memoir 116, p. 613- 

622.

Smith, R.L., Bailey, R.A., and Ross, C.S., 1961, Structural 

evolution of the Valles caldera, New Mexico, and its 

bearing on the emplacement of ring dikes: U.S. 

Geological Survey Professional Paper 424-D, p. D145- 

D149.

 1970, Geologic map of the Jemez Mountains, New 

Mexico: U.S. Geological Survey Miscellaneous 

Geologic Investigations Map 1-571, scale 1:125,000.

Smith, S.P., and Kennedy, B.M., 1985, Noble gas evidence 

for two fluids in the Baca (Valles Caldera) geothermal 

reservoir: Geochimica et Cosmochimica Acta, v. 49, p. 

893-902.

Sorey, M.L., 1985, Evolution and present state of the

hydrothermal system in Long Valley Caldera: Journal 

of Geophysical Research, v. 90, no. B13, p. 11219- 

11228.

Spiegel, Zane, 1962, Domestic water supply for Jemez, New 

Mexico: Unpublished report to U.S. Public Health 

Service, Albuquerque, N. Mex., 12 p.

Summers, W.K., 1976, Catalog of thermal waters in New 

Mexico: Socorro, New Mexico Bureau of Mines and 

Mineral Resources Hydrologic Report 4, 80 p.

Swanberg, C.A., 1983, Geothermal resources of rifts A 

comparison of the Rio Grande Rift and the Salton 

Trough: Tectonophysics, v. 94, p. 659-678.

114
Trainer, F.W., 1974, Ground water in the southwestern part 

of the Jemez Mountains volcanic region, New Mexico: 

Socorro, New Mexico Geological Society Guidebook, 

25th Field Conference, p. 337-345.

 1975, Mixing of thermal and nonthermal waters in 

the margin of the Rio Grande Rift, Jemez Mountains, 

New Mexico: Socorro, New Mexico Geological 

Society Guidebook, 26th Field Conference, p. 213-218.

 1978, Geohydrologic data from the Jemez Mountains 

and vicinity, north-central New Mexico: U.S. 

Geological Survey Water-Resources Investigations 77- 

131, 146 p. 

-1984, Thermal mineral springs in Canon de San

Diego as a window into Valles Caldera, New Mexico: 

Socorro, New Mexico Geological Society Guidebook, 

35th Field Conference, p. 249-255.

Trainer, F.W., and Lyford, F.R, 1979, Geothermal hydrology 

in the Rio Grande Rift, north-central New Mexico: 

Socorro, New Mexico Geological Society Guidebook, 

30th Field Conference, p. 299-306.

Truesdell, A.H., and Janik, C.J., 1986, Reservoir processes 

and fluid origins in the Baca geothermal system, Valles 

Caldera, New Mexico: Journal of Geophysical 

Research, v. 91, no. B2, p. 1817-1833.

Union Geothermal Company of New Mexico, 1981, 

Computer modeling of potential impacts of 50 Mwe 

commercial development of the Redondo Creek 

geothermal field, New Mexico, upon geothermal fluids 

discharge into the Jemez River: Internal report, Rio 

Rancho, N. Mex.

Union Oil Company of California and Public Service 

Company of New Mexico, 1978, Geothermal 

demonstration power plant, v. 2, Technical and 

management proposal: Submitted to U.S. Department 

of Energy in response to Program Opportunity Notice 

EG-77-NO-3-1717, 31 January 1978.

U.S. Department of Energy, 1980, Final Environmental 

Impact Statement, Geothermal Demonstration 

Program, 50 MWe power plant, Sandoval and Rio 

Arriba Counties, New Mexico: U.S. Department of 

Energy Environmental Impact Statement DOE/EIS0049.

U.S. Environmental Protection Agency, 1977, National 

interim primary drinking water regulations: Office of 

Water Supply Report EPA-570/9-76-003, 159 p.

U.S. Geological Survey, 1963 and 1964, Surface water 

records of New Mexico: Santa Fe, N. Mex.

 1965 through 1974, Water resources data for New 

Mexico: Part 1. Surface water records, Part 2, Water 

quality records, Albuquerque, N. Mex.

 1975 through 1983, Water resources data for New 

Mexico: U.S. Geological Survey Water-Data Reports 

NM-74-1 through NM-82-1, Albuquerque, N. Mex.

U.S. Soil Conservation Service, 1972, Normal annual

precipitation, New Mexico: Soil Conservation Service, 

U.S. Department of Agriculture map, scale 1:500,000.

Vuataz, F.D., and Goff, Fraser, 1986, Isotope geochemistry 

of thermal and nonthermal waters in the Valles caldera, 

Jemez Mountains, northern New Mexico: Journal of 

Geophysical Research, v. 91, no. B2, p. 1835-1853.

Vuataz, F.D., Goff, Fraser, Fouillac, Christian, and Calvez, 

Jean-Yves, 1988, A strontium isotope study of the VC1 core hole and associated hydrothermal fluids and 

rocks from Valles caldera, Jemez Mountains, New 

Mexico: Journal of Geophysical Research, v. 93, no. 

B6, p. 6059-6067.

Water Resources Associates, Inc., 1977, Hydrology Jemez 

Mountains, New Mexico: Scottsdale, Ariz., report 

prepared for Union Oil Company, 26 p., 3 app. (1978).

West, F.G., 1974, Dry hot rock project: Socorro, New 

Mexico Geological Society Guidebook, 25th Field 

Conference, p. 355-358.

West, F.G., Kintzinger, P.R., and Purtymun, W.D., 1975, 

Hydrologic testing Geothermal Test Hole No. 2: Los 

Alamos Scientific Laboratory Informal Report LA6017-MS,8p.

White, A.F., 1986, Chemical and isotopic characteristics of 

the fluids within the Baca geothermal reservoir, Valles 

Caldera, New Mexico: Journal of Geophysical 

Research, v. 91, no. B2, p. 1855-1866.

White, A.F., Delany, J.M., Truesdell, Alfred, Janik, Kathy, 

Goff, Fraser, and Crecraft, Harrison, 1984, Fluid 

chemistry of the Baca geothermal field, Valles caldera, 

New Mexico: Socorro, New Mexico Geological 

Society Field Conference Guidebook No. 35, p. 257- 

263.

White, D.E., 1957, Magmatic, connate, and metamorphic 

waters: Geological Society of America Bulletin, v. 68, 

p. 1659-1682.

White, D.E., Hem, J.D., and Waring, G.A., 1963, Chemical 

composition of subsurface waters: U.S. Geological 

Survey Professional Paper 440-F, 67 p.

Wilt, Michael, and Vender Haar, Stephen, 1986, A 

geological and geophysical appraisal of the Baca 

geothermal field, Valles Caldera, New Mexico: Journal 

of Volcanology and Geothermal Research, v. 27, p. 349- 

370.

Woltz, David, 1972, The chemistry of groundwaters in the 

Jemez area and a magnetic survey of a potential source 

of magnetic fluids: Albuquerque, University of New 

Mexico, unpublished M.S. thesis, 90 p.

Wood, G.H., and Northrop, S.A., 1946, Geology of the 

Nacimiento Mountains, San Pedro Mountain, and 

adjacent plateaus in parts of Sandoval and Rio Arriba 

Counties, New Mexico: U.S. Geological Survey Oil and 

Gas Investigations Map OM-57, scale 1:95,040.

115

£ U.S. GOVERNMENT PRINTING OFFICE: 2000 573-490 / 54003 Region No. 8
F.W. Trainer, R.J. Rogers, and M.L. Sorey GEOTHERMAL HYDROLOGY OF VALLES CALDERA AND THE SOUT

JEMEZ MOUNTAINS, NEW MEXICO U.S. Geological Survey Water-Resources Investigations Report 00-

o

o

I '5b g) §

S J2 £ | S^

^ t o o ^ ^^^

CD CD >*rH S ^

p O S g, U

. oo ^ ^^

GO OO CO X> W

H ^S r^ ^ CQ i ' i ' 10 <H HH