ON THE IMPORTANCE OF STRATIGRAPHIC CONTROL FOR VERTEBRATE FOSSIL SITES IN CHANNEL ISLANDS NATIONAL PARK, CALIFORNIA USA: AN EXAMPLE FROM A LAST-GLACIAL-AGE MAMMOTH SITE

Mammoth fossils are relatively common on the California Channel Islands. Well-preserved fossils of both Mammuthus columbi (Columbian mammoth) and M. exilis (pygmy mammoth) have been documented at hundreds of localities on the islands during the last half century or more. Despite this, the geologic context of the fossils has been described only briefly or not at all, which has hampered the interpretation of associated ¹⁴C ages and limited efforts to reconstruct paleoenvironmental conditions. We recently found a partial tusk of what appears to be a Columbian mammoth, along with several large bones and a tooth plate (also likely mammoth) at sites near Running Springs on the northwest flank of San Miguel Island. At each locality, we documented the stratigraphic context of the vertebrate remains, described the host sediments in detail, and collected charcoal and gastropod shells for radiocarbon dating. The resulting ¹⁴C ages indicate that the mammoths were present on San Miguel Island between ~20 and 17 ka (thousands of calibrated ¹⁴C years before present), shortly after the last glacial maximum. In addition to documenting the geologic context of the fossils, we describe a new set of protocols for describing and sampling sediments at paleontologic sites in Channel Islands National Park so that pertinent information is collected prior to excavation of vertebrate materials, thus maximizing their scientific value.