DEVELOPMENT OF THE CUYAMA BADLANDS AND LATE-QUATERNARY OFFSET ON THE ADJACENT BIG PINE FAULT, SOUTHERN CALIFORNIA

We have reviewed the late-stage depositional history and examined the post-depositional tectonic and geomorphic history of the Cuyama Basin, in the western Transverse Ranges, California using 10Be surface-exposure and optically-stimulated luminescence burial dating methods, revealing a dynamic sequence of landscape-altering events. After deposition in the ancestral Cuyama Basin ceased sometime since ca. 1 Ma, basin-fills were deformed and eroded, forming an undulating erosion surface on top of which alluvium of the San Emigdio Mesa was deposited between >70 ka and ~15 ka B.P. (with major alluviation ending by ~28 ka B.P.). Subsequently, major incision and drainage network development formed the Cuyama Badlands by incising into the deformed Cuyama Basin sediments. Localized deposition of alluvial fans sourced from the Pine Mountain massif were deposited near the elevation of the Cuyama River between 25 and 15 ka B.P., and have since been deformed and offset by the Big Pine Fault ~10 m, providing a latest Quaternary vertical slip-rate estimate of ~1.5 m/kyr for the western Big Pine Fault in the upper Cuyama Valley. The Big Pine Fault has no confirmed record of historic rupture; however our results suggest the likelihood of multiple reverse-slip rupture events since ~15 ka B.P.