Climate change triggered sedimentation 1033 Copyright © 2007 John Wiley & Sons, Ltd. Earth Surf. Process. Landforms 33, 1033–1046 (2008) DOI: 10.1002/esp Earth Surface Processes and Landforms Earth Surf. Process. Landforms 33, 1033–1046 (2008) Published online 13 September 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/esp.1600 Climate change triggered sedimentation and progressive tectonic uplift in a coupled piedmont– axial system: Cuyama Valley, California, USA Stephen B. DeLong 1 * Jon D. Pelletier 1 and Lee J. Arnold 2 1 University of Arizona, Department of Geosciences, 1040 E 4th Street, Tucson, AZ, 85721, USA 2 Oxford Luminescence Research Group, School of Geography and the Environment, University of Oxford, Mansfield Rd, Oxford OX1 3TB, UK Abstract Channels on the north-facing piedmont of the Sierra Madre range in Cuyama Valley, California have alternated between three process regimes during the late Quaternary: (1) vertical incision into piedmont alluvium and older sedimentary deposits; (2) lateral erosion; and (3) sediment accumulation. The state of the piedmont system at a given time has been controlled by upstream sediment flux, regional tectonic uplift and incision of the axial Cuyama River. To better understand the timing and to attempt to interpret causes of past geomorphological processes on the Sierra Madre piedmont, we mapped the surficial geology and dated alluvial deposits using radiocarbon, cosmogenic and optical dating methods. Four primary episodes of sedimentation have occurred since ca. 100 ka, culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka. Fill terraces in Cuyama Valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces. Their vertical spatial arrange- ment is a record of progressive regional tectonic uplift and concomitant axial Cuyama River channel incision migrating up tributary piedmont channels. Subparallel longitudinal terrace profiles which have a linear age–elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints ~1 m kyr -1 of regional uplift affecting the Cuyama River and its tributaries. Sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments. It is possible that increased precipitation during the Last Glacial Maximum was caused by both continental-scale circulation pattern reorganization and increased Pacific storm frequency and intensity caused by ‘early warming’ of nearby Pacific Ocean surface waters. Older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes, but may correlate with previous periods of increased precipitation. Copyright © 2007 John Wiley & Sons, Ltd. Keywords: Piedmont; Quaternary climate; sedimentation; tectonics; Cuyama Valley *Correspondence to: S. B. DeLong, Arizona State University, School of Earth and Space Exploration, Bateman Physical Sciences Center F-wing, Room 686, Tempe, AZ, 85287, USA. E-mail: sdelong@asu.edu Received 27 February 2007; Revised 10 July 2007; Accepted 12 July 2007 Introduction Suites of inset piedmont fill terraces in arid regions are records of episodic sedimentation caused by changes in upstream sediment and water flux. Pedimentation and strath terrace formation by lateral fluvial erosion can occur when channel sediment flux is insufficient to trigger major alluviation, but high enough to prevent vertical incision into the channel bed (Hancock and Anderson, 2002). Variable climate is widely understood as a cause of episodic piedmont sedimentation (and intervening fluvial entrenchment and lateral erosion). Where past climates have acted on separate catchments in similar ways, these flights of fill terraces are often assumed to be age-equivalent (Ritter et al., 1995). The primary models of piedmont response to variation in climate in the southwestern USA (California, Arizona and Nevada) generally can be characterized by process-response and to some extent, geography. In Arizona and the Mojave Desert, sedimentation during the Pleistocene–Holocene transition is widely thought to be a result of climate