Abstract

The northwest-striking Campo Grande fault of trans-Pecos Texas has a surface trace of about 45km. It divides the downthrown, central part of the Hueco basin, which contains as much as 2850m of Cenozoic fill, from the shallower northeastern flank that has 150-300m of fill. This normal fault is composed of three main en echelon segments, which are composed of numerous en echelon fault strands that are 1.5-10 km long at the surface. These strands strike N25°-75°W and dip 60°-90° southwestward. Erosion-resistant calcrete (stage IV-V) at the surface aids in preserving scarp heights of between 1.5 and 11.5m and scarp slopes of between 4° and 17°. Surface analysis of faulted upper Tertiary and Quaternary units along the southeastern Campo Grande fault segment indicates that successively younger units have less displacement. The last surface rupture was late Pleistocene. On the hanging wall of one fault strand, faulted calcic soil horizons (stage III) as much as 1m thick with vertical separations of 1-2 m indicate at least five episodes of fault movement, sediment deposition, and surface stabilization since middle Pleistocene time. The maximum vertical offset during the latest surface rupture was about 1-1.5m.

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