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.