Abstract

The Garlock fault–Slate Range area in southeastern California is known from geologic evidence to have been tectonically active during very late Cenozoic time. Historic fault scarps have not been observed, but comparisons of successive surveys along five bench-mark lines in the area indicate systematic elevation changes that can be explained as continued tectonic activity along known geological structures. The Garlock fault displays no vertical creep southeast of the Slate Range, but creep may be occurring west of that area. North of the fault, in the southwest corner of the Great Basin, the north-northwest–trending Slate Range anticline and Argus–Slate Range syncline appear to be active where bench-mark lines cross them. South of the fault, the east-northeast–trending Dome Mountain anticline and Pilot Knob Valley syncline appear active. Maximum rates of elevation change were 3.56 cm in 2 mo and 12.70 cm over 4 yr; surveys made decades apart, however, show rates that range from 0.07 to 0.27 cm/yr. Short periods of rapid change appear to be separated by long periods of no change (or reversals). The four bench-mark lines that were resurveyed 29 to 41 yr later had maximum elevation change rates of 0.01 to 0.02 cm · km−1 · yr−1; this would result in 45° of tilting along a 1-km line in 5 to 10 m.y.

The axial trends of the two pairs of anticlines and synclines are nearly normal to each other. However, the stresses causing them do not appear to be decoupled along the Garlock fault inasmuch as east-northeast folding is apparently also occurring just north of it. Two stress patterns, either alternating or reflecting deformation in differing crustal horizons, appear required to explain the observed folding plus left slip on the fault. Neither stress pattern is compatible with extension tectonic theories of the Great Basin, and this region appears to be an anomalous block restricted to the southwest corner of the province.

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