Coastal flooding and the 1861-2 California storm season

A series of large storms attributed to Atmospheric River conditions struck the California coast in the winter of 1861-2. Although historical accounts document inland flooding, little is known about how the 1861-2 storms impacted the now heavily-developed California coast. Here we show that the 1861.2 storms emplaced a deposit of beach sand up to 50 cm thick over 450 m inland within a southern California salt marsh. This deposit is unprecedented in the post-European sediments of the marsh and more extensive than that derived from any other historical event. It is comparable in scale to hurricane and tsunami washover fans in back-barrier environments along other coastlines. The presence of overwash deposits in Carpinteria suggests that the 1861.2 storm season was erosive enough to remove coastal barriers, allowing for inundation of parts of the coastline currently developed. Efforts to prepare for a recurrence of an 1861-2-like storm season should address potential coastal impacts; likewise, interpretations of past washover deposits should consider these unusually prolonged stormy periods in addition to hurricane and tsunami inundation.