MOUNTAIN-FRONT DEVELOPMENT AND TECTONIC SETTING AS RECORDED IN THE PLIO-PLIESTOCENE ALLUVIAL-FAN CONGLOMERATES OF THE WHITE/INYO MOUNTAINS, OWENS VALLEY, CALIFORNIA

Plio-Pliestocene deposits of the White/Inyo Mountains piedmont of the Owens Valley, California appear to record major tectonic events during that period of the region’s history, including initiation of range-front faulting, one or more shifts in the locus of faulting, and dip-slip motion that has built the modern White and Inyo Mountains. The goals of the research described here include mapping the extent, nature, environment of deposition, morphological expression, modern geometry, and provenance of these piedmont deposits. This work has involved field mapping, measurement of fanglomerate bedding using 3-point solutions, and measurement of stratigraphic sections with the goal of showing paleographic reconstructions at one or more time slices through the study area. Strike and dip values were determined by measuring the x,y,z coordinates of trios of points on a given contact and solving for orientation using a numerical 3-point solution. Precise elevation measurements were made with a reflectorless laser rangefinder shot to a fixed point, while horizontal coordinates were measured using a differential GPS (DGPS) system. Precise measurements of alluvial-fans stratal geometry are used to define discrete depositional units and to document tectonic tilting. The nature of these Plio-Pleistocene piedmont deposits, their distribution, and the history of subsequent tectonic deformation validate the hypothesis that a major tectonic shift occurred in the late Pliocene on the White Mountains frontal fault leading to the rapid growth of structural and topographic relief between the Owens Valley and the White/Inyo Mountains blocks.