CORVALLIS, Ore. - An Oregon State University scientist will begin probing undersea sediments off Isla Espíritu Santo in the Sea of Cortez this spring, searching for evidence of ancient peoples who may have lived in the region thousands of years ago before melting ice-age glaciers raised ocean levels.

If his techniques work, the OSU archaeologist hopes to begin in-depth near-shore surveys off the Pacific Northwest coast in hope of finding potential underwater archaeology sites that could help reveal when people first came to the western hemisphere.

Though it may sound like searching for a needle in a haystack, says OSU archaeologist Loren Davis, some of the same strategies apply as when searching for terrestrial dig sites.

"The ocean is way too big to conduct random sampling, so you want to look for locations where people would be," said Davis, an associate professor in OSU's Department of Anthropology. "The key is to determine where the shoreline was prior to about 6,000 years ago, then use the contours of this now-submerged landscape to determine where potential sites may be - such as near river channels, near estuaries, or on certain points of land."

The project is more than speculative; Davis and his colleagues already have made one foray into the waters off Isla Espíritu Santo in 2008 and were able to locate a probable archaeological site on the west side of the island. The team chose the area for a pilot project because they had excavated an early terrestrial shell midden site nearby. The ancient peoples who had made the early shell midden would have accessed marine resources from a coastline now submerged beneath the sea.

"It didn't hurt that the water is much shallower, warmer and clearer than you get off Oregon," he added with a laugh.

With funding from OSU's Bernice Huber Charitable Trust, Davis and his colleagues did some initial surveys in 2006 using simple tools - a small motorboat, a fish finder and a handheld GPS instrument - to obtain data on the seafloor's bathymetry. They used these data to create digital maps of what the coastal landscape would look like if the ocean was about 50 meters lower.

Based on the digital model, they chose an area between a tiny island and Isla Espíritu Santo, at the convergence between a submerged estuary and a rocky headland, which would offer a range of marine species for ancient peoples.

The National Geographic Society was impressed with the team's predictive model and provided funding in 2008 for limited test excavations in underwater locales. Though limited to handheld tools, Davis and his colleagues found multiple piles of shells as well as stones that appeared to have been altered and used as tools by prehistoric peoples.

But Davis is cautious about reading too much into the findings.

"You'd expect to find shells in the ocean, but the distribution of shells was curious because they were largely limited to marine animals that had some kind of economic value to coastal foragers - pearl oysters and other big, meaty clams," Davis said. "At other random locations along the island, we found much greater diversity, with as many as 37 different species. So the shells appeared to be possibly discarded by people, not random.

"We also recovered stones with features that are consistent with prehistoric tool production; however, many things can alter the appearance of stone and we must eliminate the possibility that natural processes created these items," he added. "At the end of the day, though, we determined that if we had found the same evidence on land, we would have called that a viable archaeological site."

The National Oceanic and Atmospheric Administration concurred, and is funding a return trip for Davis and colleagues from the University of California at Santa Barbara to explore more of Isla Espíritu Santo. This time, Davis and UCSB scientists Mike Glassow and Amy Gusick hope to create a more detailed map of the undersea terrain and use more powerful equipment to retrieve core samples and to facilitate large excavation of underwater sites.

Davis said he hopes the techniques are successful enough to encourage funding from federal agencies or private donors to begin exploring the waters off Oregon for similar sites.

"More than half of Oregon's archaeology sites are likely located offshore, out to 30 miles or so," Davis said. "And we think we can find them."

Davis and his colleagues have created an initial reconstruction of what the central Oregon coastline was like some 15,000 years ago and point to a large area they call Heceta Bay, into which drained the ancient Alsea and Siuslaw rivers. That bay would have been half as large as San Francisco Bay, Davis said, and its estuaries would have drawn early peoples for its clams, mussels, crab, oysters, fish and other food sources.

Another potential location is off Brookings, where Rainbow Rock extends its formation of glassy chert into the Pacific Ocean. Ideal for making stone tools, the rocky outcrop would have "drawn people like a beacon," Davis said.

Finding precise areas where ancient settlements or camps were located, when they are under a couple hundred feet of rugged Pacific Ocean, won't be easy, Davis admits. The first step is to use new data, including seafloor mapping now under way by OSU oceanographer Chris Goldfinger, to determine where old river channels might be. Submerged river valleys, he reasons, are great places for ancient sediments - and any sites they might contain - to be preserved along Oregon's offshore areas.

When the scientists can hone in on potential hotspots, Davis said, they would need to use remote sensing equipment to image the sub-seafloor, then take a series of core samples to evaluate whether ancient terrestrial sediments are preserved.

"Oregon's turbulent past does make this a difficult area in which to work," Davis said. "Past earthquakes will have caused undersea landslides that shift the sediments and the subduction of the tectonic plates no doubt has further distorted the terrain. But we think that there are a lot of viable sites right off our coastline that could provide a wealth of scientific information."

And what does he hope to find?

"The magic number is 14,500 calendar years ago," Davis said. "That's when the accepted evidence points to human habitation at sites from Monte Verde, Chile, to Oregon. But people didn't arrive overnight. It is likely that they begin arriving earlier, perhaps by 15,500 years ago - and the evidence of their arrival is likely just a few miles off our own coastline."

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Loren Davis, 541-737-3849