Geomorphic response to uplift along the Dragon's Back pressure ridge, Carrizo Plain, California

Abstract

We used high-resolution topography, geomorphic mapping of active surface processes, and geologic mapping to study the topographic and erosional response of small drainage basins to rock uplift along the Dragon's Back pressure ridge along the San Andreas fault in the Carrizo Plain, California. We infer the history of deformation experienced by ~40 small drainage basins formed in poorly consolidated sedimentary rocks. A space-for-time substitution directly images the erosional and topographic responses to deformation. Progressive deformation and rock uplift are accompanied by increases in channel steepness and basin relief. As uplift ceases, channel concavity rapidly increases, causing channels to undercut hillslopes—this undercutting promotes the consumption of hillslopes by landsliding. This undercutting also causes basin relief to be greatest after uplift has stopped. This analysis indicates that channels of the Dragon's Back pressure ridge respond to changes in rock uplift rates over thousands of years, whereas hillslope processes may take more than an order of magnitude longer to adjust to changes in rock uplift rates. Our study directly measures changes in erosional processes due to the initiation and cessation of rock uplift, which can typically only be inferred using numerical models, by direct field observations.