Channel Islands National Park: Paleontological resource inventory (public version)

Abstract

Channel Island National Park (CHIS), incorporating five islands off the coast of southern California (Anacapa Island, San Miguel Island, Santa Barbara Island, Santa Cruz Island, and Santa Rosa Island), has an outstanding paleontological record. The park has significant fossils dating from the Late Cretaceous to the Holocene, representing organisms of the sea, the land, and the air. Highlights include: the famous pygmy mammoths that inhabited the conjoined northern islands during the late Pleistocene; the best fossil avifauna of any National Park Service (NPS) unit; intertwined paleontological and cultural records extending into the latest Pleistocene, including Arlington Man, the oldest well-dated human known from North America; calichified “fossil forests”; records of Miocene desmostylians and sirenians, unusual sea mammals; abundant Pleistocene mollusks illustrating changes in sea level and ocean temperature; one of the most thoroughly studied records of microfossils in the NPS; and type specimens for 23 fossil taxa. Paleontological research on the islands of CHIS began in the second half of the 19th century. The first discovery of a mammoth specimen was reported in 1873. Research can be divided into four periods: 1) the few early reports from the 19th century; 2) a sustained burst of activity in the 1920s and 1930s; 3) a second burst from the 1950s into the 1970s; and 4) the modern period of activity, symbolically opened with the 1994 discovery of a nearly complete pygmy mammoth skeleton on Santa Rosa Island. The work associated with this paleontological resource inventory may be considered the beginning of a fifth period. Fossils were specifically mentioned in the 1938 proclamation establishing what was then Channel Islands National Monument, making CHIS one of 18 NPS areas for which paleontological resources are referenced in the enabling legislation. Each of the five islands of CHIS has distinct paleontological and geological records, each has some kind of fossil resources, and almost all of the sedimentary formations on the islands are fossiliferous within CHIS. Anacapa Island and Santa Barbara Island, the two smallest islands, are primarily composed of Miocene volcanic rocks interfingered with small quantities of sedimentary rock and covered with a veneer of Quaternary sediments. Santa Barbara stands apart from Anacapa because it was never part of Santarosae, the landmass that existed at times in the Pleistocene when sea level was low enough that the four northern islands were connected. San Miguel Island, Santa Cruz Island, and Santa Rosa Island have more complex geologic histories. Of these three islands, San Miguel Island has relatively simple geologic structure and few formations. Santa Cruz Island has the most varied geology of the islands, as well as the longest rock record exposed at the surface, beginning with Jurassic metamorphic and intrusive igneous rocks. The Channel Islands have been uplifted and faulted in a complex 20-million-year-long geologic episode tied to the collision of the North American and Pacific Places, the initiation of the San Andreas fault system, and the 90° clockwise rotation of the Transverse Ranges, of which the northern Channel Islands are the westernmost part. Widespread volcanic activity from about 19 to 14 million years ago is evidenced by the igneous rocks found on each island.