Coupled tectonic deformation and geomorphic degradation along the San Andreas Fault system

Tectonically active landscape development and the interaction between deformation and degradation are investigated by a combination of field observations and theoretical analysis.;Following the 1992 Landers, California earthquake, we repeated topographic and photographic surveys of original forms and initial modifications of faulted landforms southeast of the Galway Lake Road. Fault scarp profiles had different slope angles above and below the rupture and a small free face. Original channel surfaces stepped down over fracture-bounded blocks. Erosion was controlled by rainsplash and slumping, but surface flows drove knickpoints back by as much as 50 cm. The last similar rupture may have been several thousand years ago.;In a model for hillslope development in areas of active tectonics, the continuity equation for material transport (a function of distance from the divide to the power m, local slope to the power n, and a rate constant, ;The late Quaternary geomorphic history of Wallace Creek along the San Andreas fault zone in the Carrizo Plain, California calibrates the hillslope development model. We assume that the southwest facing scarp was exposed by lateral offset of a southeast sloping shutter ridge and by vertical offset related to local deformation. We obtained ;Geomorphic and geologic mapping of the San Andreas fault zone in the Elkhorn Hills (southeastern Carrizo Plain) indicate that the Dragon's Back (the largest and southeasternmost pressure ridge in the Carrizo Plain) is offset through a relatively stationary uplift zone along the San Andreas fault. A southwest dipping reverse fault underlies the Northern Elkhorn Hills and probably intersects the San Andreas fault. The footwall of that reverse fault may provide the localized uplift source for the Dragon's Back. As the Northern Elkhorn Hills are moved into the relatively stationary Big Bend, they are progressively deformed and degraded.