Santarosae Island
Santarosae Island (Image courtesy of Brian Fulfrost and Jack Watts)

Until 10,000 to 11,000 years ago, California's Northern Channel Islands were connected as one large island known as Santarosae, the east end of which was separated from the mainland by a strait roughly 10-12 km wide. During the last glacial maximum, when sea levels were ~100-120 meters lower than today, Santarosae’s land area was 3-4 times larger than the modern islands. As sea levels rose, the island shrunk, eventually separating into Anacapa, Santa Cruz, Santa Rosa, and San Miguel islands.

Other than humans, the only large land mammals that appear to have crossed the Santa Barbara Channel to Santarosae were wooly mammoths (Mammuthus columbi), which evolved into a dwarf island mammoth (Mammuthus exilis) averaging 4-5 feet high at the shoulder, then went extinct about 13,000 years ago. Santarosae was also home to an extinct giant mouse (Peromyscus nesodytes), numerous seabirds and waterfowl—including an extinct flightless duck (Chendytes lawi)—and a variety of marine mammals.

Climate was cooler and wetter near the end of the Pleistocene and fossil plant and pollen records show that conifers (pines, fir, etc.) were more extensive on Santarosae. Modeling of paleo-shorelines suggests that kelp forests were also more abundant than today and must have supported a wealth of marine resources (fish, sea otters, abalones, seabirds, etc.). The lack of large terrestrial predators (bears, saber-tooth cats, mountain lions, wolves, etc.) also made Santarosae a refuge for large populations of geese and other waterfowl, as well as tens of thousands of seals and sea lions. Combined with a variety of edible plants (seaweeds, pine nuts, acorns, blue dick bulbs, and many more), the rich and diverse food resources of Santarosae would have been highly attractive to early maritime peoples.

Arriving at least 13,000 years ago, humans may have disrupted the natural ecosystems of Santarosae through hunting, landscape burning, the introduction of dogs and possibly foxes, and other activities. Humans may also have contributed to the extinction of island mammoths ~13,000 years ago, but no definitive evidence for hunting of mammoths has yet been found. Archaeological sites dated to ~12,000 years ago show that a variety of shellfish, fish, birds (including Chendytes), and marine mammals were being harvested by Paleocoastal peoples. By about 8000 years ago, we have also found evidence for human impacts on some shellfish populations and near-shore ecosystems.

Paleocoastal Project team members are actively studying these long-term changes in island landscapes and seascapes, ocean temperatures, fire history, vegetation and faunal communities, hydrology, dune building, soil formation and erosion, and other ecological variables over the last 20,000 years. Natural changes are then compared to changes in human settlement, subsistence, technology, and demography to construct a comprehensive picture of the historical ecology of the islands, their ecosystems, and the complex interactions between island peoples and their natural world.

With rising postglacial seas flooding ~70% of the land area of Santarosae, island landscapes have changed dramatically since the end of the last glacial period. Such changes pose significant problems for archaeologists searching for Paleocoastal sites, most of which were probably located near now submerged shorelines. Even today, accelerating sea level rise and coastal erosion threatens to destroy many Channel Island archaeological sites, adding a sense of urgency to our work.