Mojave River Valley Museum
Geology - Mojave Preserve
Some Mesozoic deformational features of regional extent crop out in the western and
north-central parts of the EMNSA. These deformational features are reflections of shortening
shown by brittle-style thrust plates developed in the foreland of the Cordilleran thrust belt and
ductile-style nappes in southeastern California and Arizona (Burchfiel and Davis, 1971, 1977,
1981; Howard and others, 1980; Snoke and Miller, 1988; Miller and Barton, 1990).
Generally east-directed thrust faults, present in the Cowhole Mountains and the Clark
Mountain Range areas, may be Middle Triassic(?) through Early Jurassic (Burchfiel and Davis,
1981). In the Cowhole Mountains, metamorphosed Paleozoic rocks were interpreted as having
been thrust eastward and then overlapped unconformably by the Lower Jurassic Aztec
Sandstone. However, Busby-Spera (1988) and Busby-Spera and others (1989) presented
evidence that the sandstone is Middle Jurassic and may overlie a normal, not thrust, fault. In
the Clark Mountain Range, some east-directed thrust faults were cut by small dioritic plutons
originally dated at 190 and 200 Ma by K-Ar (Burchfiel and Davis, 1981) but now known as
Late Jurassic. Latest Early Cretaceous thrusting there placed Paleozoic strata over the Early
Cretaceous Delfonte volcanic rocks. This thrust was then intruded by plutons of the mid-
Cretaceous Teutonia batholith (Burchfiel and Davis, 1971, 1981; Fleck and others, in press).
A similar sequence of faulting, although not as well constrained by dated rock bodies, holds in
the New York Mountains.