On a rugged island just offshore from Ventura County, archaeologists have turned up evidence of some of the oldest human activity in coastal Southern California.

On Santa Cruz Island, the largest of the Channel Islands, researchers have found three sites scattered with ancient tool-making debris and the shells of harvested shellfish.

The youngest of the three sites has been dated to 6,600 BCE, but based on the types of tools found at the other two, archaeologists say they may be as much as 11,000 to 12,000 years old.

The artifacts are traces of what’s known as the Island Paleocoastal culture, descendants of migrants who moved south from Alaska along the Pacific at the end of the last Ice Age.

These ancient seafaring people were some of the earliest inhabitants of California’s southern coast, said Dr. Jon Erlandson, an archaeologist with the University of Oregon who reported the new finds.

“To colonize the islands, they clearly had boats and used them to hunt marine mammals, fish, and birds, and gather shellfish, seaweeds and plant foods,” he said.

“In all likelihood, the Island Chumash of historic times were, or are, descended, at least in part, from these Paleocoastal peoples.”

These ancient islanders left behind no traces of structures, at least that have been found so far, but a subtle abundance of their presence remains, like piles of abalone and mussel shells, unique barbed stone points, and distinctive crescent-shaped tools whose exact purpose remains unclear.

Using these and other clues, Erlandson and his colleagues have discovered Paleocoastal sites not only on Santa Cruz, but have also detected dozens of others throughout the Channel Islands.

Previous research had revealed Ice Age sites on San Miguel and Santa Rosa Islands, he said, and soon a pattern began to emerge among the places where Paleocoastal people left their mark. [See more discoveries in the Channel Islands: “11,000-Year-Old Seafaring Indian Sites Discovered on California Island“]

The ancient sites tended to have some kind of natural shelter nearby, as well as access to resources like rock and fresh water, and a commanding view of the island’s coastline.

So Erlandson’s team searched for areas on Santa Cruz Island that had all of these attributes, and they found the new sites — right where they predicted.

“Initially, we started examining three geographic features we felt would have pulled people away from [the island’s] coastlines that were submerged by rising seas: caves and rockshelters, freshwater springs, and toolstone outcrops,” Erlandson said.

“We added overlook sites later as our surveys revealed that they, too, were important.

“That same predictive model is now paying dividends on Santa Cruz Island.”

The first site he and his team recorded was high on a bluff looming more than 60 meters above the ocean.

There, the researchers found more than 100 chipped stone artifacts, mostly leftovers from the tool-making process, along with a handful of flake tools and the remnants of the crescent-shaped tool that’s been found elsewhere on the islands.

On another nearby bluff, the team then found a matching site, with another hundred-odd bits of chipped stone, another piece of a crescent tool, and a trash pile of cast-off mussel shells that had been stripped of their meat.

In addition to providing clues about the Paleocoastal diet, the shells also provided dates for when they were harvested, based on their levels of carbon-14.

Lab analysis showed one shell sample to be 8,560 to 8,725 years old.

[Discover how Paleocoastal people used petroleum 8,000 years ago: “Ancient California Islanders Relied on Drifting ‘Tarballs’ for Petroleum, Study Finds“]

The similarity between these two sites suggests that they served similar functions for the island’s ancient occupants, Erlandson said.

“The two coastal sites may have been workshops and overlook sites that were used relatively briefly by Paleocoastal peoples,” he said.

“Similar to some of our early sites on San Miguel Island and Santa Rosa Island, the occupants appear to have brought some shellfish to the location to dine on.”

Erlandson pointed out that the sites were far from shore — and they had been even farther from the water thousands of years ago, when sea levels were lower during the Ice Age.

So the towering height of the sites must have offered some advantage to the ancient mariners, although what it was remains unclear.

“We’re still trying to figure this out, but the sites offer commanding views of adjacent shorelines and waters,” Erlandson said.

“In some cases, they may have been used to watch where seals and sea lions were hauling out on beaches, or to keep an eye out for other humans.

“One way or the other, the strategic viewshed seems to be significant.”

Farther inland, the team discovered a third site, about 5 kilometers from the modern shoreline, on a stream terrace.

Erlandson believes this was where, more than 20 years ago, a student found and removed several stone tools, including three crescents — a finding Erlandson’s team sought to confirm.

The team first found a few dozen human-made stone flakes in the area, but no specific artifacts that could be tied to Paleocoastal or any other particular culture.

Then, nearby, they found a much denser patch of artifacts, including several biface blades, some chert flakes, and the fragment of a small stone point.

Such an assemblage of tools is a lot like those that have been found at many of the older, datable sites elsewhere on the Channel Islands, Erlandson said, and those other sites typically included crescents as well.

So that spot is likely where the three crescents had been found, he concluded, and it — along with the first overlook site — are probably some the earliest known sites on Santa Cruz Island.

“We haven’t yet found datable organic remains, but I suspect based on the number of crescents that it is among the older Paleocoastal sites on the island,” he said.

“Well-dated sites on San Miguel Island and Santa Rosa Island that have multiple crescents tend to be Terminal Pleistocene [11,500 to 12,500 years] in age.”

There’s a lot that remains to be understood about Island Paleocoastal culture, Erlandson said — among them, the precise purpose of those curious, crescent-shaped tools.

“I’ve written and thought a lot about crescents,” he said.

“They probably had multiple use-lives, but I think they were made primarily to serve as transverse projectile points used in bird hunting, a shotgun approach to shooting at flocks of birds in flight.

“On Santa Rosa Island, two stratified sites with crescents have produced numerous crescents associated with abundant bird bones, including geese and ducks.

“In the Far West, they are also closely associated with wetlands of the Pacific Flyway.”

And there’s much else about the deep past of the remote, rugged island that remains to be discovered, Erlandson said.

Owing to the fact that sea levels were so much lower 12,000 years ago, many of the sites used by Paleocoastal people are probably now underwater, he added.

For now, the picture of life in Southern California at the end of the Ice Age is faint enough that these few scatterings of stone artifacts could hold a trove of new knowledge. [Learn about related recent find: “Nearly 9,000 Artifacts Uncovered in California Desert, Spanning 11,500 Years of History“]

“We are contributing to a broader understanding of where the first Americans came from, the diversity of their adaptations, and the nature of their lives on the Channel Islands,” he said.

“Significantly, because nearly two-thirds of these islands have been submerged by rising post-glacial sea levels, we are looking at the proverbial tip of the iceberg.

“Many more Paleocoastal sites were probably located on the vast submerged landscape that surrounds the islands, and we are now turning our attention to this largely unexplored realm beneath the sea.”

Erlandson and his colleagues report their findings in the journal Paleoamerica.

Erlandson, J., Gill, K., Glassow, M., & Gusick, A. (2016). Three Paleocoastal Lithic Sites on Santa Cruz Island, California PaleoAmerica, 2 (1), 52-55 DOI: 10.1080/20555563.2016.1141741