ACTIVE TECTONICS AT WHEELER RIDGE, SOUTHERN SAN-JOAQUIN VALLEY, CALIFORNIA

Wheeler Ridge is an east-west-trending anticline that is actively defo rming on the upper plate of the Pleito-Wheeler Ridge thrust-fault syst em, Holocene and late Pleistocene deformation is demonstrated at the e astern end of the anticline where Salt Creek crosses the anticlinal ax is. Uplift, tilting, and faulting, associated with the eastward growth of the anticline, are documented by geomorphic surfaces that are high er and older to the west, Faulting and associated folding is propagati ng eastward, as indicated by increases in both the degree of surface d issection and the degree of soil development from east to west. Distin ct topographic areas having distinct degrees of surface dissection, bo unded by tear faults, suggest that faulting and folding have propagate d eastward in discrete segments, Numerical dates indicate (1) the anti cline is propagating eastward at a rate of about 30 mm/yr (about 10 ti mes 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 an tecedent stream was defeated, forcing the stream east around the nose of the fold; today drainage through the ridge is by way of two anteced ent streams (water gaps) east of the mind gap; and (4) the rate of upl ift 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 Whee ler Ridge support the hypothesis that climatic perturbations are prima rily responsible for producing geomorphic surfaces such as alluvial fa n segments and river terraces-tectonic perturbations deform the surfac es.