Collapsed Canyon Heads: A Sign of Fluid Induced Mass Wasting. H. Gary GREENE1, Peter EICHHUBL2, and Norm MAHER2 1Monterey Bay Aquarium Research Institute and Moss Landing Marine Laboratories, Moss Landing, CA 95039 2Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039-0628 The heads of some submarine canyons along the California margin exhibit collapse structures that suggest failure due to pore fluid expulsion. Two submarine canyons, Ano Nuevo Canyon and Arguello Canyon, in central California are particularly noteworthy in their geomorphologic similarity and collapsed heads. Both of these canyons display concentric down dropped terraces with steep circular headwall scarps. These canyons notch the distal edge of the continental slope and are associated with other canyon heads that may have also originated from fluid induced mass wasting. Both of the collapsed heads of Ano Nueveo and Arguello canyons are located in a transpressional tectonic setting and are adjacent to known gas and petroleum sources. Specifically, the head of Ano Nuevo Canyon is located above a bedrock ridge that bounds the southern part of the hydrocarbon bearing Outer Santa Cruz Basin. The heads of Arguello Canyon lie along a structural high that bounds the southern end of the petroleum-rich Santa Maria Basin. In addition, the heads of these canyons overlie zones previously mapped as continuous gas-charged reflectors that generally lie at shallow depths (30 m) and are near the base of unconsolidated Quaternary sediments. We speculate that these unusual canyon head morphologies result from fluid-induced mass wasting. The close proximity of the canyon heads to local hydrocarbon sources and reservoirs suggest that gas or fluid discharge on the sea floor that induced failure may have come from these reservoirs. Conversely, some failures may result from the expulsion of biogenic gas.