New evidence for eolian activity and mammoths on Santa Rosa Island prior to the Last Glacial Maximum

Sea-level fluctuations due to the growth and decay of continental ice sheets of the Quaternary exert a strong influence on geologic processes along coastlines. The California Channel Islands are no exception to this, and many studies have been conducted that focus on the extremes of these glacial-interglacial cycles, such as the last glacial period (marine isotope stage [MIS] 2) and the last interglacial period (MIS 5). Far less attention has been paid to intermediate time periods between these extremes, such as MIS 4. Here, we present two very different geologic records from this time period that show how sea-level change affected the nature of sedimentation on the northern shore of Santa Rosa Island. On the northwestern coast of Santa Rosa Island, thick eolian sediments accumulated between ~80 ka and ~45 ka due to a lowered sea level that exposed carbonate-rich skeletal sands that had accumulated during the last interglacial period. On the central part of the northern coast of Santa Rosa Island, thick alluvial sediments were deposited between 80 ka and 47 ka, similar to the time of eolian sedimentation to the west. A mammoth tusk discovered within these deposits is only the third stratigraphically controlled mammoth fossil on the Channel Islands that dates prior to MIS 2. Its discovery adds to the evidence that mammoths migrated to the Channel Islands from mainland California prior to the Last Glacial Maximum.