Abstract

A gravity investigation consisting of some 900 stations was conducted over an area of approximately 3,500 km2 between the Eagle Mountains and the Colorado River in the southeastern Mojave Desert to define the major anomalies. The data were reduced to the complete Bouguer anomaly and presented on a contour map. The density contrasts that exist between the basin sedimentary rocks and the underlying basement rock produce gravity anomalies that can be readily delineated by gravity surveys. Several gravity anomalies are associated with regional structural trends, particularly faults. Two-dimensional model analyses along profiles across five major anomalies are presented to show the distribution and depth of sedimentary deposits.

Subsurface geology in the area is poorly known. Analysis of the gravity anomalies, however, indicates that the basement beneath the sedimentary basins is highly faulted, consisting of complex structures and rapidly varying rock types similar to those in the mountain ranges of the area. In the center of the several subdivisions of the Chuckwalla Valley, depths to basement range from less than 200 m to more than 2 km. The Palen Valley is shallow in the northern section yet reaches a probable depth of over 1.5 km in its southern portion. The Palo Verde Valley east of the Chuckwalla Valley is divided into two separate structural styles. A northwest-trending sedimentary basin in the north has a maximum depth of at least 2 km, while basement to the south is generally more flat and less deep. The structural and geological information inferred from the gravity data and resultant anomalies provides important input toward a better understanding of the geology in the area.

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