Active tectonics at Wheeler Ridge, southern San Joaquin Valley, California

Wheeler Ridge is an east-west-trending anticline that is actively deforming on the upper plate of the Pleito-Wheeler Ridge thrust-fault system. Holocene and late Pleistocene deformation is demonstrated at the eastern end of the anticline where Salt Creek crosses the anticlinal axis. Uplift, tilting, and faulting, associated with the eastward growth of the anticline, are documented by geomorphic surfaces that are higher and older to the west. Faulting and associated folding is propagating eastward, as indicated by increases in both the degree of surface dissection and the degree of soil development from east to west. Distinct topographic areas having distinct degrees of surface dissection, bounded by tear faults, suggest that faulting and folding have propagated eastward in discrete segments. Numerical dates indicate (1) the anticline is propagating eastward at a rate of about 30 mm/yr (about 10 times the rate of uplift); (2) folding was initiated about 400 ka; (3) a prominent wind gap was formed during Q3 time (about 60 ka) when an antecedent stream was defeated, forcing the stream east around the nose of the fold; today drainage through the ridge is by way of two antecedent streams (water gaps) east of the wind gap; and (4) the rate of uplift at the easternmost and youngest (past 1 k.y.) part of the fold is at least 3 mm/yr. Investigations of the tectonic geomorphology of Wheeler Ridge support the hypothesis that climatic perturbations are primarily responsible for producing geomorphic surfaces such as alluvial fan segments and river terraces-tectonic perturbations deform the surfaces.