Evidence of Repeated Wildfires Prior to Human Occupation on San Nicolas Island, California

Abstract

Understanding how early humans on the California Channel Islands might have changed local regimes requires a baseline knowledge of the frequency of natural wildfires on the islands prior to human occupation. A sedimentary sequence that was recently discovered in a small canyon on San Nicolas Island contains evidence of at least 24 burn events that date to between ~37 and 25 ka (thousands of calibrated 14C years before present), well before humans entered North America. The evidence includes abundant macroscopic charcoal, blackened sediments, and dis- crete packages of oxidized, reddish-brown sediments that are similar in appearance to sedimentary features called fire areas on Santa Rosa Island and elsewhere. Massive fine-grained sediments that contain the burn evidence are inter- preted as sheetwash deposits and are interbedded with coarse-grained, clast-supported alluvial sediments and matrix- supported sands, pebbles, and cobbles that represent localized debris flows. These sedimentary sequences suggest that the catchment area above our study site underwent multiple cycles of relative quiescence that were interrupted by and followed by slope instability and mass wasting events. Our 14C-based chronology dates these cycles to well before the arrival of humans on the Channel Islands and shows that natural wildfires occurred here, at a minimum, every 300-500 years prior to human occupation.