U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5166

Questa Baseline and Pre-Mining Ground-Water Quality 

Investigation. 24. Seismic Refraction Tomography for 

Volume Analysis of Saturated Alluvium in the Straight 

Creek Drainage and Its Confluence with Red River, 

Taos County, New Mexico
Questa Baseline and Pre-Mining Ground-Water Quality 

Investigation. 24. Seismic Refraction Tomography for 

Volume Analysis of Saturated Alluvium in the Straight 

Creek Drainage and Its Confluence With Red River, 

Taos County, New Mexico

By Michael H. Powers and Bethany L. Burton

Scientific Investigations Report 2006–5166

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

 U.S. Geological Survey, Reston, Virginia: 2007

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

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

resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Powers, Michael H., and Burton, Bethany L., 2007, Questa baseline and pre-mining ground-water quality investigation. 24. Seismic refraction tomography for volume analysis of saturated alluvium in the Straight Creek drainage 

and its confluence with Red River, Taos County, New Mexico: U.S. Geological Survey Scientific Investigation Report 

2006–5166, 19 p.
iii

Contents

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

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

Previous Work ................................................................................................................................................3

Seismic Refraction Profiles .........................................................................................................................3

Data Collection......................................................................................................................................3

Data Analysis.........................................................................................................................................6

Tomography Results .............................................................................................................................8

Seismic Line 5...............................................................................................................................8

Seismic Line 6...............................................................................................................................8

Seismic Line 7...............................................................................................................................8

Seismic Line 8.............................................................................................................................12

Seismic Line 9.............................................................................................................................12

Estimating Volume of Alluvium ..................................................................................................................12

Conclusions...................................................................................................................................................15

Acknowledgments.......................................................................................................................................18

References Cited..........................................................................................................................................18

Figures

1. Topographic map showing location of Straight Creek model area, New Mexico.............2

2. Photograph of SE Straight scar..................................................................................................2

3. Photograph of valley floor of Straight Creek............................................................................3

4. Topographic map showing locations of nine seismic lines on Straight Creek

 and Red River near the confluence of Straight Creek with Red River...............................4

5. Velocity-depth models of seismic lines 1 through 4 ...............................................................5

6. Seismic line 5; velocity-depth models generated during processing

 of seismic data and velocity-depth model..............................................................................7

7–11. Diagrams of topography, source and receiver locations, first-arrival

 travel-time curves, and velocity-depth models and interpretation

 7. Seismic line 5 ....................................................................................................................9

 8. Seismic line 6 ..................................................................................................................10

 9. Seismic line 7 ..................................................................................................................11

 10. Seismic line 8...................................................................................................................13

 11. Seismic line 9...................................................................................................................14

12–14. Digital elevation models along Straight Creek near its confluence with Red 

 River showing

 12. Topography ......................................................................................................................15

 13. Configuration of bedrock surface ................................................................................16

 14. Configuration of water table ........................................................................................17

15. Pie diagrams showing proportions of wet and dry alluvium calculated in Red

 River valley and in Staight Creek drainage ..........................................................................18
iv

Conversion Factors

SI to Inch/Pound

Mulitply By To obtain

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft)

meter (m) 1.094 yard (yd)

Abbreviations used in this report

kg kilogram

km kilometer, kilometers

lb pound

m meter, meters

mps meters per second

Delta-TV offset distance, travel time, and apparent velocity

DEM digital elevation model

NAD27 North American Datum of 1927

NGVD29 National Geodetic Vertical Datum of 1929

USGS United States Geological Survey

UTM Universal Transverse Mercator

WET wavepath eikonal travel-time tomography
Questa Baseline and Pre-Mining Ground-Water Quality 

Investigation. 24. Seismic Refraction Tomography for 

Volume Analysis of Saturated Alluvium in the Straight 

Creek Drainage and Its Confluence With Red River, 

Taos County, New Mexico

By Michael H. Powers and Bethany L. Burton

Abstract

As part of a research effort directed by the New Mexico 

Environment Department to determine pre-mining water quality of the Red River at a molybdenum mining site in northern 

New Mexico, we used seismic refraction tomography to create 

subsurface compressional-wave velocity images along six 

lines that crossed the Straight Creek drainage and three that 

crossed the valley of Red River. Field work was performed 

in June 2002 (lines 1–4) and September 2003 (lines 5–9). We 

interpreted the images to determine depths to the water table 

and to the top of bedrock. Depths to water and bedrock in 

boreholes near the lines correlate well with our interpretations 

based on seismic data. In general, the images suggest that the 

alluvium in this area has a trapezoidal cross section.

Using a U.S. Geological Survey digital elevation model 

grid of surface elevations of this region and the interpreted 

elevations to water table and bedrock obtained from the 

seismic data, we generated new models of the shape of the 

buried bedrock surface and the water table through surface 

interpolation and extrapolation. Then, using elevation differences between the two grids, we calculated volumes of dry and 

wet alluvium in the two drainages. The Red River alluvium is 

about 51 percent saturated, whereas the much smaller volume 

of alluvium in the tributary Straight Creek is only about 18 

percent saturated. When combined with average ground-water 

velocity values, the information we present can be used to 

determine discharge of Straight Creek into Red River relative 

to the total discharge of Red River moving past Straight Creek. 

This information will contribute to more accurate models of 

ground-water flow, which are needed to determine the premining water quality in the Red River.

Introduction

This report summarizes results from the use of seismic 

refraction tomography in a study area in northern New 

Mexico, at and near the confluence of Straight Creek with 

Red River, to determine approximate geometry and volumes 

of dry and saturated alluvium above bedrock. It is one of

many publications presenting results of a U.S. Geological 

Survey study of ground-water quality in the Red River 

upstream from Questa, New Mexico (for example, Lovetere 

and others, 2004; Maest and others, 2004; Nordstrom, in 

press; and Vincent, in press). This information will be used 

to constrain ground-water models for a larger area of interest 

that encompasses Molycorp molybdenum mine (fig. 1) about 

10 miles west of the study area. 

The town of Questa is located beside the Red River in 

north-central New Mexico (fig. 1), 8 kilometers (km) west 

of and downstream from the Molycorp molybdenum mine, 

which is preparing for closure. The New Mexico Environment 

Department is required to ensure that pre-mining water quality 

exists in the river at Questa in fulfillment of a requirement for 

mine closure. That department invited the U.S. Geological 

Survey to contribute research toward the determination of the 

pre-mining quality of river water at the mine site. 

Many natural erosional scars were present at the mine site 

before mining, and they still exist in the Red River drainage 

both upstream and downstream from the mine site. The scars 

are underlain by mineralized zones of pyrite-rich rocks that 

have weathered and eroded on the steep topography, removing 

all vegetative cover and allowing large amounts of material to 

be shed during rainstorms and snow melt (Ludington and 

others, 2004). This sulfide-rich material oxidizes when in 

contact with surface water and then contributes acidic water to 

the drainage system (Briggs and others, 2003; Smith, in press). 

That acidic water is then able to dissolve high concentrations 

of heavy metals. Thus, the natural watershed and the issue of 

pre-mining water quality are complex.
Straight Creek drains into Red River upstream from the 

mine site. Because its slopes contain natural scars (for example, SE Straight scar, fig. 2), it was identified as an analog for 

the mine site before mining activity. A similar but larger scar 

exists at the head of the Straight Creek drainage. Thunderstorms can move large amounts of debris down the valley, as 

indicated by mud plastered onto tree trunks (fig. 3). Alluvial 

material in the Straight Creek drainage is composed primarily 

of sulfide-rich scar detritus (Plumlee and others, in press). 

Accurate ground-water models (McAda and Naus, in 

press; Naus and McAda, 2006) of the Straight Creek area 

(figs. 1 and 4) require detailed mapping of both dry and saturated alluvium. Seismic refraction tomography studies (White, 

1989; Docherty, 1992; Zhang and Toksoz, 1998; Powers and 

Burton, 2004; Sheehan and others, 2005) provide subsurface 

seismic velocity measurements along survey transects that 

can be used to determine the depth to the water table and to 

bedrock.

Figure 1. Straight Creek model area (red rectangle), New Mexico; located upstream from a molybdenum 

mine undergoing closure in 2006. Red River flows west through the southern part of model area. Base map 

modified from DeLorme XMap 4.502.0, 3-D TopoQuad Base Map, New Mexico North Region 3, 1999.

Figure 2. SE Straight scar, viewed from the eastern slope 

above Straight Creek southeast toward the town of Red River. 

Red River

Red River

Study

area

0 1 2 3 4 5 6 7 KILOMETERS

   Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
In late May 2002, the U.S. Geological Survey acquired 

four lines of seismic data across the valley of Straight Creek 

(fig. 4) and analyzed them by use of a commercial refraction 

tomography method. We were pleased to discover that the 

highly variable depths to water table and bedrock were readily 

interpreted from the resulting velocity images. This initial 

seismic effort and the results are described in Powers and 

Burton (2004) and are briefly summarized in the next section 

of this report. In late September 2003, we acquired five more 

seismic lines across the confluence of Straight Creek with Red 

River and across the valley of Red River (fig. 4). This report 

describes the analysis and interpretation of lines 5–9 and provides images and calculated volumes of the alluvial material in 

the model area by use of interpolation and extrapolation of all 

the interpreted subsurface contact information.

Previous Work

The need for information about bedrock geometry in 

the Straight Creek area for use in ground-water modeling 

first arose in 2001. Lucius and others (2001), who applied 

electrical methods, discovered a lack of contrast in electrical 

properties between alluvium and underlying bedrock. In 2002, 

four lines of seismic data were acquired with the intent to 

process and interpret for reflections that indicated the bedrock 

interface. Owing to many factors—such as strong surface 

waves, rough interfaces, strong offline scattered energy, and 

loss of high-frequency content—a bedrock reflection across 

the profile was not confidently determined. A high-velocity 

refractor, however, was indicated by the pattern of first-arrival 

times. Evidence of this refractor led to an analysis of the data 

by use of a commercial seismic refraction tomography method 

(Rohdewald, 2003). The resulting images of compressional 

wave velocity versus depth and lateral position revealed interpretable contacts between dry and wet alluvium and between 

alluvium and bedrock. The interpreted contacts correlate well 

with borehole information. Analyses of seismic lines 1–4 

(Powers and Burton, 2004) are summarized in the following 

paragraph.

Because of dry conditions, low noise requirements, 

budget limits, steep terrain, limited access to forested areas, 

and other factors, the initial seismic effort at this site used a 

hand-held sledgehammer as the sole wave source. The four 

seismic lines ranged in length from 60 to 240 meters (m), and 

all crossed the valley from bedrock on one side to bedrock 

on the other (fig. 5). Each line had a different but constant 

receiver spacing; the geophone intervals for lines 1–4 were 

0.75, 1.0, 1.5, and 2.0 m, respectively. Source positions were 

located between every receiver to provide the dense coverage necessary to produce a reflection image. We found that 

the refraction tomography method did not require use of all 

source-receiver pairs to create reasonable images. However, 

the dense acquisition of data allowed the use of data subsets in 

analyses to determine the optimal coverage for future costefficient surveys that do not sacrifice accuracy. This experience was essential for planning the effective acquisition and 

imaging of five longer lines that include spans across the valley of the Red River.

Seismic Refraction Profiles

Data Collection

The locations and lengths of lines 5–9 (fig. 4) were 

determined in conjunction with a geomorphologist and with 

ground-water modelers in order to best contribute information 

that will improve the accuracy of ground-water flow models, 

which in turn support the overall research goal of determining 

pre-mining water quality. The lines are numbered according 

to priority and were acquired in that order. Given the common 

constraints of time, money, equipment, access, and environmental sensitivity, our objective was to create, along as many 

profiles as possible, accurate subsurface images that showed 

the shape and depth of the water table and of the bedrock 

surface.

A 96-channel seismic system, using cables with a 

maximum of 5 m between geophone take-outs, can be 

deployed in a single spread of live geophones a maximum 

of 480 m. This distance was adequate to cover the longest 

planned line. We acquired each line in one day by deploying 

all 96 geophones with cables in a single live spread and 

acquiring shot locations through the spread from one end of 

the line to the other. Tests on previous lines determined that 

a shot location spacing of three times the receiver spacing 

produced accurate images of suitable resolution within our 

time and cost budget.

Figure 3. The valley floor of Straight Creek, looking downstream, 

mantled with poorly sorted alluvial material shed from natural 

erosion scars and transported by thunderstorm runoff. Mudline on 

tree (arrow) marks high water during thunderstorm events.

Seismic Refraction Profiles   
Figure 4. Locations of nine seismic lines in study area. Lines 1–4 across 

upper Straight Creek are discussed in Powers and Burton (2004). Lines 5–9, 

near the confluence of Straight Creek and Red River, are discussed in this 

report, which uses all nine lines to estimate the volume of basin alluvium in 

the model area. Borehole SC–8A and borehole SC–8B (not labeled) lie within 

2 m of each other. Base map modified from U.S. Geological Survey map Red 

River, New Mexico, 1:24,000. 

N

EXPLANATION

Seismic line, 2002

Seismic line, 2003

   Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 5. Velocity-depth images of seismic lines 1–4 at the same scale. Alluvium and bedrock 

distinguished by use of a color scale corresponding to common velocities of earth materials: dark 

yellow, unsaturated and unconsolidated fill (velocity 400–1,500 mps); blue, water-saturated sediment 

(velocity 1,600–2,000 mps); red, consolidated rock (velocity >3,000 mps).

HORIZONTAL DISTANCE, IN METERS

HORIZONTAL DISTANCE, IN METERS

VELOCITY

RELA

, METERS PER SECOND

TIVE ELEVATION, IN METERS RELATIVE ELEVATION, 

IN METERS

Line 4

Line 3

Line 2

Line 1

Seismic Refraction Profiles   
Accurate first-arrival time picks on the data records are 

essential for meaningful tomographic velocity images. The 

energy source must be strong enough to generate clear firstarrival responses on the geophones for accurate time picks. At 

this site, the energy from a 9-kilogram (kg) hand-held hammer 

swung onto a steel plate placed flush on the ground generated 

first-arrival signals that were distinct from noise in the data out 

to source-to-receiver distances of 35 m (worst case) to 200 m 

(best case). Lines 5–9 ranged in length from 240 to 400 m, 

so that use of the hammer was effective only in the center 

portions of each line. For the ends of the lines, where distances 

to far geophones were greatest, permission was received from 

the Questa District Office of the Carson National Forest to use 

small, buried charges of 1⁄3 pound (lb) binary explosive. Small, 

binary charges are reasonably priced, portable, and powerful 

enough to generate good first-arrival signals at large sourceto-receiver distances. Binaries (in which powder and fluid 

are stored in separate containers and are not hazardous until 

mixed) are safe and legal to transport. The major drawback 

to explosives is the need to drill holes in which to place the 

charges to prevent surface noise and disruption in sensitive 

locations. At this site, we used a hand-held electric rock drill 

powered by a portable 4,400-watt generator mounted on a 

small four-wheel all-terrain vehicle.

The receiver interval distance was set according to the 

physical line length, and each line extended across the valley 

from bedrock on one side to bedrock on the other. Shot 

locations were marked according to source type (hammer or 

buried charge), and off-end shots that extended past the first 

and last receivers provided a better image of the bedrock 

on the ends of the lines. The hammer was used for source 

locations in the middle of each line, which included locations 

near State Highway 38, parallel to Red River, and other 

cultural structures. A laser surveying instrument was used to 

measure topography along each line.

Data Analysis

For each of the lines 5–9, the first-arrival times and acquisition geometry, including topography, were used to compute 

subsurface velocity. First-arrival times were picked manually for every source-receiver pair showing clear first-arrival 

energy. Noisy data were excluded because the inversion routines that compute velocity as a function of depth and lateral 

distance are very sensitive to the accuracy of the first-arrival 

time picks. Bad picks will result in velocity errors. Missing or 

sparse data, where questionable picks are left out, will result 

only in a loss of detail in the velocity results.

Two commercial software packages were used to make 

the computations. Sheehan and others (2005) compare and 

discuss three commercial packages used for seismic refraction 

tomographic analysis, including the two used here.

The first package, Rayfract by Intelligent Resources Inc., 

uses a two-step procedure (Rohdewald, 2003). In the first step, 

automatic one-dimensional inversions are performed under 

every source-receiver midpoint using a top-down method, 

labeled Delta-TV (offset distance, travel time, and apparent 

velocity) that assumes multiple layers. Within each layer, 

velocity is increased linearly with depth such that the energy 

path is a circular arc (Gibson and others, 1979; Rohdewald, 

Intelligent Resources, Inc., written commun., 2004). This 

method, which is applied vertically for each midpoint and then 

along the line for all midpoints, results in an initial velocity 

model that is used in the second step. The second step is an 

iterative, constrained, matrix-minimization routine (named 

wavepath eikonal travel-time tomography) (WET) that determines a whole-model solution that best matches calculated 

travel times determined by use of forward modeling. In this 

case, it follows an algorithm described in Schuster and

Quintus-Bosz (1993). 

The second package, GeoCT-II by GeoTomo LLC, 

accepts any starting model, such as a single constant velocity 

or the best result from any previous analysis. It also performs 

an iterative, constrained, matrix-minimization inversion that 

determines a whole-model solution that best matches travel 

times calculated by use of forward modeling. However, this 

package follows an algorithm described in Zhang and Toksoz 

(1998) that differs substantially from the algorithm used in the 

Rayfract package in both the inversion steps and the forwardmodeling routine. The GeoCT-II package also allows known 

velocity-depth information, as from a borehole, to be entered 

and used as a constraint during the computations. 

Our velocity images were created by using the Rayfract 

package first and then the GeoCT-II package. Three images 

were generated in the first step by use of Rayfract (Delta-TV) 

and then three images with the second step (WET). By using 

the data from line 5, minimum, average, and maximum velocity images were generated with the Delta-TV method (left 

column, fig. 6A). Parameters were changed as needed and the 

images regenerated until they looked reasonable according 

to our understanding of local geology. The average velocity 

image from the first step was then used to start the second 

step, and three more images were generated with the WET 

algorithm (right column, fig. 6A). Again, parameters were 

changed as needed to make the images look reasonable; however, in general, our parameter adjustments changed the image 

very little. The average velocity profile generated by the final 

run of the WET algorithm was interpreted as the best Rayfract 

solution.

The GeoCT-II package allows the user to start with any 

model and to control lateral and vertical smoothing parameters, maximum and minimum velocity, and the number of 

iterations within an inversion run. As stated previously, known 

velocity-versus-depth information at a given position along 

the line can be used as a fixed-position constraint. Our use 

of the package in this case included inversion runs using the 

final Rayfract WET image as the starting model for comparison with runs based on a simple, constant starting model. We 

examined many combinations of lateral and vertical smoothing as well as the influence of variations on the general level 

of smoothing. The fixed-position constraint was used where 

 Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 6. Seismic line 5. A, Velocity images. Sets of three images generated by different algorithms in two steps by use of Rayfract 

software. Best output of first step was starting model in second step. Image labeled “Average Velocity, WET” accepted as the 

final Rayfract image. Algorithm abbreviations: Delta-TV, offset-distance, travel time, and apparent velocity; WET, wavepath eikonal 

travel-time tomography. B, Final velocity image generated by use of GeoCT-II resulted from many combinations of starting models and 

constraints. It does not precisely represent subsurface geology but can be used to interpret general subsurface features. Alluvium 

and bedrock distinguished by use of a color scale corresponding to common velocities of earth materials: dark yellow, unsaturated 

and unconsolidated fill (velocity 400–1,500 mps); blue, water-saturated sediment (velocity 1,600–2,000 mps); red, consolidated rock 

(velocity >3,000 mps).

HORIZONTAL DISTANCE, IN METERS

VELOCITY, IN METERS PER SECOND

RELATIVE ELEVATION, IN METERS

A

HORIZONTAL DISTANCE, IN METERS

VELOCITY, IN METERS PER SECOND

RELATIVE ELEVATION, 

IN METERS

B

Seismic Refraction Profiles 
borehole information was available and with knowledge of 

bedrock outcrops at the line ends. The final GeoCT-II velocity image of line 5 (fig. 6B) shows apparent minor bedrock 

steps near the surface on the west (left) side of the image; 

those steps are the graphical result of requiring bedrock at the 

line end to match known outcrops by using a fixed-position 

constraint. Travel-time constraints on velocity at the line ends 

are weak, and the fixed-position constraint was used to force 

the bedrock slopes to approach the surface where bedrock 

contacts were visible in the field. This step geometry is an 

artifact of the lateral smoothing and probably should not be 

interpreted strictly.

Tomography Results

The first-arrival travel-time curves and the velocity image 

results are described below for lines 5–9. The final Rayfract 

and GeoCT-II velocity images of each line were independently 

interpreted for simple contacts between dry and saturated 

alluvium (that is, at the water table), and between saturated 

alluvium and bedrock. These interpretations of individual 

images were based only on the respective velocity image and 

the general correlation of velocity with type of material at this 

location. The two interpretations were placed together, and we 

interpreted a final geologic profile using all other knowledge 

of the site and that gained through the inversion process. A 

final geologic cross section honored subsurface features that 

appeared consistent as the inversion parameters of the software packages were varied. 

Seismic Line 5

 Line 5 is oriented east-west near the mouth of Straight 

Creek, where the creek flows into the valley of the Red River 

(fig. 4), and it is the lowest elevation line that crosses the 

Straight Creek drainage. It crosses the upper portion of the 

Red River municipal water treatment facility. No nearby boreholes exist that can be used to verify contact depths.

Hammer data were important for data acquisition on 

this line. For line 5 only, we used shotgun shell casings filled 

with black powder instead of buried charges at the start of the 

acquisition (dark red circles along the topographic profile, 

fig. 7A). They were slow to deploy because of the need to dig 

holes and to prepare the triggering mechanism, and at this 

site they did not provide energy greater than that of a hammer blow. They also produced a marked and inconsistent time 

delay between triggering of the system and initiation of energy 

propagation. In processing, a bulk shift to earlier times was 

determined and applied to all black powder first-arrival time 

picks. Black powder shell casings were not used for lines 6–9. 

It is appropriate to consider the seismic profile image 

of this line in concert with those of the four lines presented 

in figure 5, as they all represent cross sections of the Straight 

Creek drainage as it broadens downslope. In this context, the 

interpretation of the relatively open and smoothly arcuate bedrock valley with a maximum depth of about 60 m (fig. 7B) is a 

reasonable approximation of the true geology and is presented 

with high confidence.

Seismic Line 6

Line 6, the longest of the nine lines, diagonally crosses 

the confluence of Straight Creek and the Red River (fig. 4). 

To ensure coverage of possibly deep bedrock, extra shots were 

positioned beyond the ends of this line to increase source-toreceiver distances. We relied more on buried charges for this 

line and less on the hammer (fig. 8A). The line crosses the 

highway (stations 60–65 at 240–260 m downline) and ends 

just short of the river.

Independent interpretations of the final velocity images 

from the two packages both agree with borehole data; this 

agreement provides confidence in the general interpretation 

of geology (fig. 8B). Two boreholes, one drilled into alluvium 

(SC–5A) and one into bedrock (SC–5B), are located 158 m 

downline and 18 m offline to the northeast (fig. 4). The depths 

to water table and bedrock as indicated in these boreholes 

(Naus and others, 2005) are displayed on the interpreted section (fig. 8B). The Red River does not meet the water table 

under line 6. Dry alluvium extends about 20 m under the river. 

Similarly, a borehole drilled several hundred meters downstream from this location passed through dry alluvium under 

the river (Naus and others, 2005; Blanchard and others, in 

press). The deepest part of the Red River valley is not located 

under the current river location at the southern edge of the 

drainage but is more in the central part of the valley just north 

of the highway. The bedrock surface at the Straight Creek 

drainage opening rapidly changes slope as it drops into the 

valley of Red River, whereas the water table retains a relatively gentle slope across the confluence.

Seismic Line 7

 Line 7 is oriented north-south across the valley of Red 

River (fig. 4) and passes near the entrance to the Red River 

water treatment facility. The central part of the line, where the 

hammer was used, was located along the entrance road into 

the facility. Evidently the hammer source on the road surface 

generated only weak energy in the alluvium. The short gray 

curves indicate unclear first-arrival energy generated beyond 

stations 10–15 (35–52 m) (fig. 9A). Although the buried 

charges at both ends of the line provided information about 

the velocity at depth, the refraction tomography method yields 

more accurate images when the velocity solutions can be 

determined from the surface downward. The result is increased 

uncertainty in the accuracy of the image under the central part 

of line 7 owing to the loss of first-arrival time picks at midtimes in this segment (about stations 30–50). The borehole 

(AWWT–1) is located less than 10 m offline to the west and 

shows a depth to water that is a good match with the seismic 

interpretation. The water table still does not reach the surface 

at the river (270 m downline) although it increases in elevation 

just north of the river. 

 Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 7. Seismic line 5. A, Locations of sources and receivers on topographic profile and first-arrival travel-time curves. Station 

interval 3 m; total line length about 283 m. Truncated curves or dashed sections indicate missing data where noise, low energy, 

or road or river crossings prevented confident picks. B, Final velocity images generated from first-arrival times by use of Rayfract 

and GeoCT-II software. Independent interpretations of each image used to generate the interpreted, color-coded, geologic cross 

section. All three images at same scale (1 in. = 110 m) and without vertical exaggeration.

A

STATION NUMBER

STATION NUMBER

RELATIVE ELEVATION, 

IN METERS

TIME, IN MILLISECONDS

EXPLANATION

Receiver

Hammer shot

Explosive shot

Shotgun shells

Hammer shot—Dashed 

 where uncertain

Buried explosive charge—Dashed 

 where uncertain

Top of saturated alluvium as 

 strictly interpreted

Top of bedrock as strictly interpreted

Unsaturated and unconsolidated 

 fill—Velocity 400–1,500 mps

Water-saturated sediment—Velocity 

 1,600–2,000 mps

Consolidated rock—Velocity 

 >3,000 mps

B

DISTANCE, IN METERS

RELATIVE ELEVATION, IN METERS

VELOCITY, IN METERS PER SECOND

Seismic Refraction Profiles 
Figure 8. Seismic line 6. A, Locations of sources and receivers on topographic profile and first-arrival travel-time curves. 

Station interval 4 m; total line length almost 400 m. Gray travel-time curves dashed where estimated because location lacked 

geophone. For this long line crossing the Red River valley, more buried charges were used to allow confident time picks. B, Final 

velocity images generated by use of two software packages; images agree with borehole data. Slope of bedrock along Straight 

Creek increases where Straight Creek flows into Red River, but slope of water table retains its gentle upstream gradient. All three 

images at same scale (1 in. = 132 m) and without vertical exaggeration. See Naus and others (2005) for description of boreholes. 

EXPLANATION

Receiver

Hammer shot

Explosive shot

Hammer shot—Dashed 

 where uncertain

Buried explosive charge—Dashed 

 where uncertain

Top of saturated alluvium as

 strictly interpreted

Top of bedrock as strictly interpreted

Unsaturated and unconsolidated 

 fill—Velocity 400–1,500 mps

Water-saturated sediment—Velocity 

 1,600–2,000 mps

Consolidated rock—Velocity

 >3,000 mps

A

STATION NUMBER

STATION NUMBER

RELATIVE ELEVATION, 

IN METERS TIME, IN MILLISECONDS

B

DISTANCE, IN METERS

RELATIVE ELEVATION, IN METERS

VELOCITY, IN METERS PER SECOND

10 Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 9. Seismic line 7. A, locations of sources and receivers on topographic profile and first-arrival travel-time curves. 

Station interval 3.5 m; total line length 310 m. Hammer source at stations 20–50 did not provide clear first-arrival time picks at 

long distances; note short gray curves in this region. End-of-line charges provide some information about velocity at depth, but 

accuracy of the image is reduced owing to missing information. Borehole near the seismic line confirms depth to water table 

near this region. B, Final velocity images and interpretation. The two velocity images look quite different but when interpreted 

show only small uncertainty, mainly in depth to central bedrock surface. Interpretation closely matches water level in borehole 

AWWT–1. All three images at same scale (1 in. = 132 m) and without vertical exaggeration.

EXPLANATION

Receiver

Hammer shot

Explosive shot

Hammer shot—Dashed 

 where uncertain

Buried explosive charge—Dashed 

 where uncertain

Top of saturated alluvium as

 strictly interpreted

Top of bedrock as strictly interpreted

Unsaturated and unconsolidated 

 fill—Velocity 400–1,500 mps

Water-saturated sediment—Velocity 

 1,600–2,000 mps

Consolidated rock—Velocity

 >3,000 mps

A

STATION NUMBER

STATION NUMBER

B

RELATIVE ELEVATION, 

IN METERS

TIME, IN MILLISECONDS

DISTANCE, IN METERS

RELATIVE ELEVATION, IN METERS

VELOCITY, IN METERS PER SECOND Seismic Refraction Profiles 11
The final images generated by the two software packages 

differ in their details of water table and bedrock in this region 

(fig. 9B). General features including approximate depth to and 

nature of water table and bedrock surfaces can be confidently 

interpreted. Both images show an irregular water table. If 

one uses a little imagination, the shape of the wet-dry contact 

in the alluvium suggests that water from the Straight Creek 

drainage may be turning west (down valley) and has not yet 

or is just starting to meet groundwater from the valley of Red 

River that is moving more toward the central or southern part 

of the valley. If this is the case, then the water in borehole 

AWWT–1 comes mostly from the Straight Creek drainage (see 

Naus and others, 2005). The junction between Straight Creek 

and Red River waters appears to be just north of the highway 

(at 190–200 m) along this line. The bedrock depth can be 

confidently determined only to within ±10 m along the central 

part of this line. 

Seismic Line 8

Line 8 crosses the Red River valley downstream from line 

7 (fig. 4). The line changes heading slightly at the highway 

and again at the river, owing to difficulty in finding a direct 

route through the east end of the Fawn Lakes campground and 

across the river. The shot curves (fig. 10A) show that the hammer energy does not reach bedrock in the central, deep part 

of the line. Even the end-of-line explosive charges just barely 

manage to show a slope break indicative of bedrock velocity.

Depth to bedrock in the central part of the line was not 

well determined. However, seismic data strongly indicate 

the contact between dry and wet alluvium. The contact is 

mounded toward the northern side of the valley, suggesting 

that it is not associated with the river. The water-table level in 

borehole SC–8A is a reasonable fit to the interpretation, given 

that the borehole is more than 40 m east of the line (fig. 10B). 

The flat bedrock benches on both sides of the valley are present in the two velocity images and are supported by the traveltime data.

Seismic Line 9

Line 9 crosses the valley of Red River just upstream from 

the confluence of Straight Creek with the Red River (fig. 4). 

Travel-time curves show the predominant use of buried 

charges; only nine hammer locations, all near the highway, 

were used (fig. 11A). The curves also show good slope breaks 

in bedrock velocity, even in some curves generated by hammer 

shots. The images for this line are strongly supported by clean, 

dense data.

The final velocity images and interpretation (fig. 11B) 

show an asymmetric valley with a long, smooth slope on the 

north and a steeper, shorter slope on the south. The Red River 

at this point is at the southernmost edge of the valley, but the 

deepest bedrock surface lies to the north, toward the center of 

the line. The water table appears to be at its highest elevation 

just south of the valley center, above the deepest surface of 

bedrock.

Before acquisition and interpretation of the seismic data 

presented here, the subsurface nature of the bedrock interface 

was the subject of speculation. Three simple models of the 

cross-sectional shape of the valley—which thus constrain 

alluvium volumes—had been proposed: (1) the exposed valley 

walls extend downward without a change in slope and produce 

a V-shaped valley containing a minimal volume of alluvium, 

(2) the bedrock walls extend downward vertically to some 

fixed, flat, bedrock depth and produce a rectangular-shaped 

valley containing a maximal volume, and (3) the bedrock 

walls extended downward with slopes of about 30° dip to a 

flat bottom producing a trapezoidal valley shape containing an 

intermediate volume. Vincent described the geomorphology 

of the area and supported the trapezoidal model (Vincent, in 

press). Our seismic data interpretations (for instance, fig. 11B) 

also support the trapezoidal model.

Estimating Volume of Alluvium

A U.S. Geological Survey digital elevation model 

(DEM) of this region and subsurface information derived 

from interpretations of the nine seismic lines were combined 

with surface interpolation and extrapolation to estimate, for 

the model area, three-dimensional volumes of dry and wet 

alluvium above bedrock. Publicly available elevation values 

for the model area exist on a 10-m grid; a rectangular portion 

of that grid of elevation values was taken from the 7.5 minute 

Red River DEM (fig. 12). For each seismic line grid point, 

seismic data provide the surface elevation and the subsurface 

elevations of water table and the top of bedrock.

The area used for volume analysis is in Universal Transverse Mercator (UTM) zone 13 North, which is bounded by 

east and west X coordinates of 460140 and 460740 m, respectively, and by south and north coordinates of 4062150 and 

4063250 m, respectively. The horizontal grid is based on the 

North American Datum of 1927 (NAD27), and the elevations 

are based on the National Geodetic Vertical Datum of 1929 

(NGVD29). The area is 600 m across (east-west) and 1,100 

m long (north-south), or 0.66 km2, and it contains the Straight 

Creek drainage and a portion of the valley of the Red River 

(fig. 12). 

Topography on the alluvium has gentler gradients in 

general than the steep slopes of the exposed bedrock mountains. This slope difference and field observations were used 

to determine the approximate boundary between alluvium 

and bedrock at the surface in this area. Marking that boundary 

allowed us to separate the original DEM topography for the 

region into elevation values of exposed bedrock (on the slopes 

and high-elevation areas) and elevation values of alluvium (in 

the drainages). Surface elevation values for the area underlain by surface alluvium were blanked in the study-area grid, 

thus graphically removing the alluvium. For seismic line grid 

12 Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 10. Seismic line 8. A, Locations of sources and receivers on topographic profile and first-arrival travel-time curves. 

Station interval 2.5 m; total line length about 240 m. Hammer-source curves do not change slope (which would indicate bedrock 

velocity) in the central part of the line. B, Final velocity images and interpretation. Depth to bedrock in central part of the line 

is not well determined but is 50–70 m below elevation of river surface. Water-table mound and bedrock benches supported by 

travel-time data. All three images at same scale (1 in. = 110 m) and without vertical exaggeration.

EXPLANATION

Receiver

Hammer shot

Explosive shot

Hammer shot—Dashed 

 where uncertain

Buried explosive charge—Dashed 

 where uncertain

Top of saturated alluvium as

 strictly interpreted

Top of bedrock as strictly interpreted

Unsaturated and unconsolidated 

 fill—Velocity 400–1,500 mps

Water-saturated sediment—Velocity 

 1,600–2,000 mps

Consolidated rock—Velocity

 >3,000 mps

A

B

STATION NUMBER

STATION NUMBER

RELATIVE ELEVATION, 

IN METERS TIME, IN MILLISECONDS

DISTANCE, IN METERS

RELATIVE ELEVATION, IN METERS

VELOCITY, IN METERS PER SECOND

Estimating Volume of Alluvium 13
Figure 11. Seismic line 9. A, Locations of sources and receivers on topographic profile and first-arrival traveltime curves. Station interval 3 m; total length of line about 335 m. Coverage and data quality are very good. B, Final 

velocity images and interpretation. All three images at same scale (1 in. = 122 m) and without vertical exaggeration. 

EXPLANATION

Receiver

Hammer shot

Explosive shot

Hammer shot—Dashed 

 where uncertain

Buried explosive charge—Dashed 

 where uncertain

Top of saturated alluvium as

 strictly interpreted

Top of bedrock as strictly interpreted

Unsaturated and unconsolidated 

 fill—Velocity 400–1,500 mps

Water-saturated sediment—Velocity 

 1,600–2,000 mps

Consolidated rock—Velocity

 >3,000 mps

A

STATION NUMBER

STATION NUMBER

B

RELATIVE ELEVATION, 

IN METERS

TIME, IN MILLISECONDS

DISTANCE, IN METERS

RELATIVE ELEVATION, IN METERS

VELOCITY, IN METERS PER SECOND

14 Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 12. Configuration of absolute surface elevation values (relative to NGVD29) near confluence of Straight Creek 

and Red River. Generated from a U.S. Geological Survey digital elevation model that provides surface elevations on a 

10×10 m XY (NAD27) grid. Seismic line locations cast to nearest 10-m-grid locations. 

points, new elevations of bedrock below the alluvium were 

inserted from the seismic interpretations. The resulting grid 

contains bedrock elevation values for exposed bedrock slopes 

and for the seismic-line grid points. A surface interpolation 

and extrapolation routine was used to fill in bedrock elevations 

at the missing points between the lines to create a bedrock 

model (fig. 13). 

With the same procedure, but using the elevations of the 

water table (instead of elevations of bedrock) obtained from 

interpretations of the seismic data, we created another model 

of the area with the dry alluvium stripped away (fig 14). In this 

case, the surface mapped in the valleys is the top of saturated 

alluvium (that is, the water table). Three grids of surface elevation values were produced by this process. They are (1) the 

original topographic DEM (fig. 12), (2) the surface-elevation 

model of the top of bedrock exposed on the slopes and buried 

in the valleys (fig. 13) throughout the grid area, and (3) the 

elevations of exposed bedrock slopes and the water table in the 

valleys (fig. 14). The grid was divided into a Straight Creek 

drainage portion and a Red River valley portion. Simple grid 

subtraction and volume analysis was performed to calculate 

the approximate volumes of dry and wet alluvium in the 

Straight Creek drainage and the valley of Red River (fig. 15). 

Because only selected segments of both the Straight Creek 

drainage and the valley of Red River (those within the grid 

shown in the figures) were analyzed, the absolute volume values in cubic meters are not as meaningful as the percentages 

of wet and dry material in each drainage. In the Straight Creek 

drainage, only 18 percent of the alluvium is saturated. In the 

valley of Red River, 51 percent of the alluvium is saturated. 

This information, along with the geometry of the bedrock and 

water-table surfaces, can be used to help ground-water modelers provide a more realistic understanding of subsurface flows 

in this area.

Conclusions

We used seismic refraction tomography in the study area 

to determine accurate depth to water table and bedrock across 

the Straight Creek and Red River drainages. In so doing, we ELEVATION, IN METERS

UTM Y (m)

Seismic line

Conclusions 15
Figure 13. Configuration of top of bedrock near confluence of Straight Creek and Red River. Generated from 

surface-elevation values shown in figure 12 and bedrock elevation values determined from seismic lines by 

graphical removal of alluvium and interpolation of the bedrock surface. Seismic line locations cast to the nearest 

10-m-grid locations. 

ELEVATION, IN METERS

UTM Y (m)

Seismic line

16  Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Figure 14. Configuration of water table near confluence of Straight Creek and Red River. Generated from surfaceelevation values shown in figure 12 and from depth to the water table, defined by interpretation of seismic data. Dry 

alluvium graphically removed to reveal the water table. Seismic line locations cast to the nearest 10-m-grid locations. ELEVATION, IN METERS

UTM Y (m)

Seismic line

Conclusions 17
Figure 15. Proportions of wet and dry alluvium in valley of 

Red River and in Straight Creek drainage. Volumes of wet and 

dry alluvium computed by use of grid mathematics on surface 

elevations obtained from seismic data and then converted to 

more useful percentages.

determined that a shot-location spacing of three times the 

receiver spacing was the best choice for producing accurate, 

cost-effective images in this area. A hand-held, 9-kg hammer 

source produced clear first-arrival energy to distances of 35–

200 m, depending on noise conditions and near-surface properties. The hammer was more effective in this study area than 

buried shell casings that contained black powder, which were 

time consuming to deploy and provided weak first-arrival 

energy. A combination of 1⁄3 lb buried explosive charges for 

larger offset shots (>180 m) and the safe, portable, costeffective sledgehammer for smaller offset shots produced 

good coverage and high-quality seismic refraction data.

Images generated by two commercial refraction tomography software packages differed in consistency. We used the 

inconsistent results, along with travel-time curves displaying density and quality of data, as indicators of uncertainty. 

This approach led to interpretations that are reasonable 

geo­logically (Vincent, in press) and are a good match with 

the limited borehole control. In general our interpretations 

support a trapezoidal model, rather than a rec-tangular or 

V-shaped model, of surface-of-bedrock geometry in the study 

area.

By using seismic lines spaced no more than a few 

hundred meters apart, we were able to interpolate buried 

bedrock and water-table interfaces to determine their

respective geometries throughout the model area. Using these 

geometries, we estimated the volume of wet and dry alluvium 

in the drainages. When combined with average ground-water 

velocity values, the information we present here can be used 

to determine the discharge of the Straight Creek into the Red 

River relative to the total discharge of the Red River moving 

past the mouth of Straight Creek. Alluvium in the Straight 

Creek drainage area within our model area is only 18 percent 

water saturated; alluvium within the Red River valley portion 

of the model area is 51 percent saturated.

Acknowledgments

The authors wish to acknowledge and thank Ron Thibideaux and others of the Questa District Office of the Carson 

National Forest and Russell Church and others of the Red 

River Water Treatment facility for allowing access for this 

work. Carl Stoddard and Roy Kipfinger of the U.S. Geological Survey helped with data acquisition and worked several 

long days. This work was made possible through Geoff 

Plumlee and Kirk Nordstrom of the U.S. Geological Survey 

with funding from the USGS Water Resources Discipline 

National Research Program. Kirk Vincent of the U.S. Geological Survey provided helpful comments on the paper overall, 

and Seth Haines and Jeff Lucius, also of the U.S. Geological Survey, provided thorough technical reviews that greatly 

improved the paper and are much appreciated. Viki Bankey of 

the U.S. Geological Survey provided a helpful copy edit of the 

text, and Mary-Margaret Coates of ATA Services provided a 

comprehensive technical edit that was wonderful in detail and 

scope. The remaining shortfalls of the paper belong solely to 

the authors.

References Cited

Blanchard, P.J., Bartolino, J.R., Naus, C.A., and Morin, R.H., in 

press, Questa baseline and pre-mining ground-water quality 

investigation. 15. Methods and results of well installation, 

development, and logging and water-level data collection 

in the Red River Basin, New Mexico, 2002–2004: U.S. 

Geological Survey Scientific Investigations Report 2006–

5246.

Briggs, P.H., Sutley, S.J., and Livo, K.E., 2003, Questa baseline 

and pre-mining ground-water quality investigation. 11. 

Geochemistry of alteration scars and waste piles: U.S. 

Geological Survey Open-File Report 03–458, 17 p.

DeLorme, 1999, XMap 4.502.0, 3-D TopoQuad Base Map, New 

Mexico North Region 3: P.O. Box 298, Yarmouth, Maine 

04096.

Red River Valley alluvium

Total volume 12.74 million cubic meters

Straight Creek drainage

Total volume 3.10 million cubic meters

Dry

49 percent

6.28 million

cubic meters

Wet

51 percent

6.46 million

cubic meters

Dry

82 percent

2.54 million 

cubic meters

Wet

18 percent

0.56 million 

cubic meters

18  Questa Baseline and Pre-Mining Ground-Water Quality Investigation, New Mexico. 24. Seismic Refraction
Docherty, P.C., 1992, Solving for the thickness and velocity 

of the weathering layer using 2-D refraction tomography: 

Geophysics, v. 57, no. 10, p. 1307–1318.

Gibson, B.S., Odegard, M.E., and Sutton, G.H., 1979, Nonlinear 

least-squares inversion of traveltime data for a linear velocitydepth relationship: Geophysical Journal, v. 44, no. 2, 

p. 185–194.

Lovetere, S.H., Nordstrom, D.K., Maest, A.S., and Naus, C.A., 

2004, Questa baseline and pre-mining ground-water quality 

investigation. 3. Historical ground-water quality for the Red 

River valley, New Mexico: U.S. Geological Survey WaterResources Investigations Report 03–4186, 49 p.

Lucius, J.E., Bisdorf, R.J., and Abraham, J., 2001, Results 

of electrical surveys near Red River, New Mexico: U.S. 

Geological Survey Open-File Report 01–0331, 40 p.

Ludington, S.D., Plumlee, G.S., Caine, J.S., Bove, D.J., 

Holloway, J.M., and Livo, K.E., 2004, Questa baseline and 

pre-mining ground-water quality investigation. 10. Geologic 

influences on ground and surface waters in the lower Red 

River watershed, New Mexico: U.S. Geological Survey 

Scientific Investigations Report 2004–5245, 46 p.

Maest, A.S., Nordstrom, D.K., and Lovetere, S.H., 2004, Questa 

baseline and pre-mining ground-water quality investigation. 4. 

Historical surface-water quality for the Red River valley, New 

Mexico: U.S. Geological Survey Scientific Investigations 

Report 2004–5063, 150 p.

McAda, D.P., and Naus, C.A., in press, Questa baseline and 

pre-mining ground-water quality investigation. 22. Groundwater budget for the Straight Creek drainage basin, Red 

River valley, New Mexico: U.S. Geological Survey Scientific 

Investigations Report 2006–5165.

Naus, C.A., McAda, D.P., and Myers, N.C., 2006, Questa 

baseline and pre-mining ground-water quality investigation. 

21. Hydrology and water balance of the Red River 

valley, New Mexico: U.S. Geological Survey Scientific 

Investigations Report 2006–5040, 37 p.

Naus, C.A., McCleskey, R.B., Nordstrom, D.K., Donohoe, L.C., 

Hunt, A.G., Paillet, F.L., Morin, R.H., and Verplanck, P.L., 

2005, Questa baseline and pre-mining ground-water quality investigation. 5. Well installation, water-level data, and 

surface- and ground-water chemistry in the Straight Creek 

drainage basin, Red River valley, New Mexico, 2001–2003: 

U.S. Geological Survey Scientific Investigations Report 

2005–5088, 220 p.

Published in the Central Region, Denver, Colo.

Manuscript approved for publication August 3, 2006

Graphics by author

Edited by Mary-Margaret Coates (Contractor, ATA Services)

References Cited 19

Nordstrom, D.K., in press, Questa baseline and pre-mining 

ground-water quality investigation. 25. Summary of results 

and baseline and pre-mining ground-water geochemistry, Red 

River valley, Taos County, New Mexico, 2001–2005: U.S. 

Geological Survey Professional Paper 1728.

Plumlee, G.S., Ludington, S., Vincent, K.R., Verplanck, P.L., 

Caine, J.S., and Livo, K.E., in press, Questa baseline and 

pre-mining ground-water quality investigation. 7. A pictorial 

record of chemical weathering, erosional processes and 

potential debris-flow hazards in scar areas developed on 

hydrothermally altered rocks: U.S. Geological Survey OpenFile Report 2006–1205.

Powers, M.H., and Burton, B.L., 2004, Questa baseline and 

pre-mining ground-water quality investigation. 1. Depth to 

bedrock determinations using shallow seismic data acquired 

in the Straight Creek drainage near Red River, New Mexico: 

U.S. Geological Survey Open-File Report 2004–1236, 18 p.

Rohdewald, S.R., 2003, Rayfract manual: Intelligent Resources, 

Inc., Vancouver, B.C., Canada.

Schuster, G.T., and Quintus-Bosz, Aksel, 1993, Wavepath 

eikonal traveltime inversion—Theory: Geophysics, v. 58, 

no. 9, p. 1314–1323.

Sheehan, J.R., Doll, W.E., and Mandell, W.A., 2005, An 

evaluation of methods and available software for seismic 

refraction tomography analysis: Journal of Environmental and 

Engineering Geophysics, v. 10, no. 1, p. 21–34.

 Smith, K.S., Hageman, P.L., Briggs, P.H., Sutley, S.J., 

McCleskey, R.B., Livo, K.E., Verplanck, P.L., Lamothe, P.J., 

and Gemery, P.A., in press, Questa baseline and pre-mining 

ground-water quality investigation. 19. Leaching studies 

on scar and waste-rock materials: U.S. Geological Survey 

Scientific Investigations Report 2006–5165.

Vincent, K., in press, Questa baseline and pre-mining groundwater quality investigation 17. Geomorphology of the shallow 

alluvial aquifer of the Red River valley, New Mexico: U.S. 

Geological Survey Scientific Investigations Report 

2006–5156.

White, D.J., 1989, Two-dimensional seismic refraction 

tomography: Geophysical Journal, v. 97, p. 223–245

Zhang, Jie, and Toksoz, M.N., 1998, Nonlinear refraction 

traveltime tomography: Geophysics, Society of Exploration 

Geophysics, v. 63, p. 1726–1737.
Powers and Burton—Questa Baseline and Pre-Mining Ground-Water Quality Investigation. 24. Seismic Refraction Tomography for Volume—SIR 2006–5166

 Taos County, New Mexico Analysis of Saturated Alluvium in the Straight Creek Drainage and Its Confluence with Red River, 

Printed on recycled paper