Abstract

A review of geologic relationships across the Richardson-Hess fault system demonstrates that large-scale strike-slip separation did not occur among rocks younger than Proterozoic. Evidence against major lateral separation is: (1) Structural units of gently dipping Paleozoic strata, deformed during Columbian-Laramide orogenesis, show only 10 to 20 km (total) generally right-lateral separation across the fault system. (2) The only notable discontinuity across the fault system occurs along a prominent lineament at its south end. This discontinuity is part of a 200-km-long transition of thick Lower Cambrian quartzite and carbonate strata southwestward into argillite, and does not need to be explained by strike-slip faulting. (3) Lower Paleozoic paleogeography across the Richardson-Hess system features a complex arrangement of arches, basins, and troughs. All strata in and around these features are, at present, harmoniously juxtaposed.

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