Aeromagnetic map of the Death Valley ground-water model area, 

Nevada and California 

By D.A. Ponce and R.J. Blakely 


Prepared in cooperation with the 


Nevada Operations Office 


National Nuclear Security Administration 


U.S. Department of Energy 


(Interagency Agreement DE-A108-96NV11967)


Pamphlet to accompany 


Miscellaneous Field Studies MF-2381-D


2001 
U.S. Department of the Interior 

U.S. Geological Survey 

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INTRODUCTION 

This aeromagnetic map of the Death Valley ground-water model area was prepared from 

numerous separate aeromagnetic surveys that were gridded, merged, and described by 

Hildenbrand and Kucks (1988) and by McCafferty and Grauch (1997). These data are available 

in grid format from the EROS Data Center, U.S. Geological Survey, Sioux Falls, South Dakota, 

57198, and from the National Geophysical Data Center, 325 Broadway, E/GC4, Boulder, Colo., 

80303. Magnetic investigations of the Death Valley ground-water basin are part of an 

interagency effort by the U.S. Geological Survey (USGS) and the Department of Energy 

(Interagency Agreement DE-AI08-96NV11967) to help characterize the geology and hydrology 

of southwest Nevada and adjacent parts of California (Blakely and others, 2000b). The Death 

Valley ground-water model is located between lat 35°00’ and 38°15’N., and long 115° and 

118°W. 

AEROMAGNETIC DATA 

Aeromagnetic data for the Death Valley ground-water model were collected at various flight-line 

spacings and altitudes (Hildenbrand and Kucks, 1988; Sikora and others, 1993; McCafferty and 

Grauch, 1997). Some parts of the map are covered by more recent and detailed aeromagnetic 

surveys flown at a flight-line spacing of 400 m (1/4 mi) and a nominal flight-line elevation of 

122 m (400 ft) above the ground. Older surveys were flown at flight-line spacings of 800 to 

1,600 m (1/2 to 1 mi) and at constant barometric elevations of about 2,440 m (8,000 ft). 

Magnetic anomalies were derived by subtracting an International Geomagnetic Reference Field 

(Langel, 1992) appropriate for the year of the survey. Aeromagnetic surveys were continued 

downward, if necessary, to a flight-line elevation of 122 m (400 ft) above the ground, adjusted to 

a common datum, and merged to produce a uniform map that allows interpretations across survey 

boundaries. Because of the poor quality of the older surveys, caution should be exercised when 

interpreting short-wavelength anomalies that cross the original survey boundaries. The digital 

data set was gridded at an interval of 1 km using a computer program (Webring, 1981) based on 

a minimum curvature algorithm by Briggs (1974). The resulting grid was then interpolated to a 

200-m grid to minimize pixel size, and then it was color contoured. 

DISCUSSION 

Geologic features often produce small magnetic fields that perturb the main field of the earth and 

can be enhanced by the removal of a regional magnetic field. These measurements reflect lateral 

changes in rock magnetic properties and can be analyzed to gain insights into the threedimensional nature of the causative source. In general, aeromagnetic anomalies within the Death 

Valley ground-water model reflect volcanic rocks, calderas, granitic intrusions, and linear 

geologic features such as faults. Many of these features play an important role as aquifers or 

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confining units in the region, and their distribution is important to the understanding of the 

hydrogeologic framework of the area. 

One of the most prominent magnetic anomalies in Nevada is a broad magnetic high over the 

Spring Mountains in the southeast part of the study area. Blank (1987) attributed this anomaly to 

a concealed upwarp of Precambrian basement. Most Paleozoic rocks are relatively non-magnetic 

with one notable exception: an unusually strongly magnetized member of the Eleana Formation 

(Baldwin and Jahren, 1982) that produces a conspicuous magnetic high over the southern part of 

Shoshone Mountain in the central part of the study area. Magnetic highs are associated with the 

Wahmonie (Ponce, 1984) and Climax stocks (Healey, 1983) at Lookout Peak, in the central part 

of the study area, and Belted Range, in the northern part of the study area, respectively. Tertiary 

volcanic rocks have variable magnetic properties and play a significant role in the extensional 

history of the area and in the formation of large collapse calderas in the southwest Nevada 

volcanic field. Thick accumulations of these volcanic rocks are present in the central and 

northern part of the Death Valley ground-water model (for example, Timber Mountain and 

vicinity). Volcanic units, vertically offset by faults in the central part of Yucca Mountain just 

south of Timber Mountain, produce conspicuous anomalies that can be used to infer the strike, 

dip, and vertical offset of the magnetic units (Ponce, 1996). Alluvial deposits within the study 

area are essentially nonmagnetic and most basins have subdued magnetic anomalies with the 

exception of those basins that may contain volcanic centers (for example, Amargosa Valley). 

A number of geophysical studies were undertaken to aid in characterizing the geologic and 

hydrogeologic setting of the Death Valley ground-water model area. A summary of geophysical 

investigations at Yucca Mountain that includes gravity, magnetics, electrical methods, seismic 

methods, heat-flow, and stress data were provided by Oliver and others (1995). Recent studies 

characterized the geophysical framework of the southwestern Nevada volcanic field (Grauch and 

others, 1999; Mankinen and others, 1999) identifying a number of subsurface features that might 

control or influence ground-water flow. These features include resurgent calderas and prominent 

geophysical lineaments that probably reflect faults. Blakely and others (2000a, b) summarized 

geophysical investigations of the Death Valley regional ground-water model area. 

In this region, geophysical methods are critical to the understanding of the geologic, tectonic, and 

hydrologic framework. The diverse physical properties of rock units that underlie this region are 

well suited to geophysical investigations. The contrast in magnetic properties between preCenozoic rocks, volcanic rocks, and alluvium produces a distinctive pattern of anomalies that can 

be used to determine the sources of the anomalies and their subsurface extent. 

3 
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