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

¹ Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA
² School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, USA

View larger version (81K): [in this window] [in a new window]   Figure 1. Dragon's Back pressure ridge (DBPR) and relatively stationary uplift zone. A: Airborne Laser Swath Mapping (ALSM) topography (1 m digital elevation model [DEM]); B: geology (modified from Arrowsmith, 1995); C: total rock uplift (sensu England and Molnar, 1990) inferred from distribution of geologic contacts, assuming initially horizontal contacts; D: instantaneous rock uplift rate (assuming 33 mm/yr of right-lateral slip along San Andreas fault [SAF]); and E: along-channel profiles of basin numbers referenced to panel A (see Figure DR2 for photographs of these basins [see text footnote 1]). In A, scale at bottom of panel references locations in Figure 2. In B, QTP is undifferentiated Paso Robles Formation; Qoa is Pleistocene alluvium; QTPp, QTPt, QPTg are pink, tan, and gold members of the Paso Robles Formation; Qls indicates landslide deposits; and Qya is young alluvium. Dashed contours in B show inferred location of San Andreas fault at various depths and illustrate shallow offset of San Andreas fault that produces rock uplift within southeastern portion of landform. Inset in B shows location of study area and highlights surrounding features: WC—Wallace Creek, GF—Garlock fault, SB—Santa Barbara, and LA—Los Angeles.

View larger version (25K): [in this window] [in a new window]   Figure 2. Mean rock uplift rates along DBPR ridge line, total rock uplift (measured peak values are from Fig. 1C), local relief (mean value shown as solid line, 95% bounds shown as shaded area), residual relief (mean value shown as solid line, 95% bounds shown as shaded area), basin width (solid line shows 500 m running average), basin area (solid line shows 500 m running average), channel concavity (solid line shows 200 m running average), normalized channel steepness (solid line shows 500 m running average), landslide scar density (solid line shows 500 m running average), and gradient along nonchannel points (mean value shown as solid line, 95% bounds shown as shaded area) shown as a function of distance from SE end of Dragon's Back pressure ridge (DBPR). Different averaging window for channel concavity was selected to highlight abrupt increase in concavity following cessation of uplift. Channel concavities and steepness (calculated using methods discussed in Whipple and Tucker, 1999) were calculated for those basins over which points that displayed a clear linear trend in log area–log slope space could be identified over more than one order of magnitude change in area. Normalized channel steepness was calculated by using mean concavity for all basins (0.68).