“I think we’re on an old travel route,” he says, kicking mud from his boots. “This was undoubtedly a base camp for Paleo Indians. They would have spent more time here than they would at a hunting camp. You have to think about resources.”
Platt points west toward the slope of a nearby mountain. There — about a half-mile in the distance — archaeologists have found a chert quarry. The black rock, along with obsidian and dacite, were used to make stone tools including the knives, spear tips and hide scrapers found throughout the site. During that time, the game was abundant and the water fresh. Nearly everything they needed to survive the summer months was right here.
On a day not unlike this one 6,850 years ago, Mazama blasted 3,000 feet of mountaintop, opening a caldera five miles wide and one mile deep (today’s Crater Lake in Oregon). The sky turned dark and ash swirled down in a terrible blizzard of grit over the Pacific Northwest.
The ominous cloud drifted as far east as Billings and as far south as Reno, Nev. For a band of ancient people, the event was likely frightening. How it altered their lives, nobody really knows. But given the impacts the 1980 eruption of Mount St. Helens had on our modern civilization, Mazama — whose eruption was more than 40 times larger — would have disrupted life for hundreds of years.
“The ash is like ground-up glass,” Platt said. “It would have worn out the teeth of the animals that grazed here pretty fast. It’s perfectly possible that people may have left this site for a few hundred years. It would have been tough going and dusty.”
The ash in this particular pit is nearly a foot deep. Platt believes this spot of ground was once lower than the rest. In a trench 100 yards away, the ash layer is thinner, measuring just a few inches thick.
“I’m not going to say we’re standing on Pompeii because we’re not,” Platt said. “But because these artifacts were capped by an act of geology, we know much more than we otherwise would have.”
The Mazama eruption may have done more than darken the sky and create a storm of lung-choking ash across the Pacific Northwest. Bill Eckerle, a geoarchaeologist based in Salt Lake City who has a long history of digging in Montana, believes the Mazama eruption changed the climate. It’s his job to determine if the artifacts found here were moved by time, or if they are resting where humans discarded them thousands of years ago.
When dust-sized material falls out of the atmosphere, it buries the artifacts gently, he explains. But when a river spills its banks, the action is more intense and can move objects from their original location. It doesn’t seem like it would matter much, as the artifacts have been preserved either way. But for a sleuth like Eckerle, the difference is enormous.
“We’re trying to figure out what kind of plants and animals lived in the area, what resources were available to the people who stayed here,” he said. “The Mazama ash is real nice. It has set a wonderful marker.”
Standing near a small square trench, his face shaded from the sun, Eckerle points across the sage-covered valley and explains how it once contained cottonwoods, gooseberries and cottontails.
After the eruption, however, the wetlands turned dry. The once-flat valley filled with sediment that washed the mountains during torrential thunderstorms. That changed the contour of the land. Over time, the accumulation of sediment forced the stream into a narrow channel. In Eckerle’s words, it became “entrenched.” The dry vegetation, once captive to the upper slopes, began to spread.
“What we’ve found indicates that this area had more moisture,” he said. “It was more meadow-like, and I think the valley was wider and flatter in here. After the Mazama ash fell, it looks like we got more material coming off the slopes. A wedge of sediment worked into the valley. A drier climate prevailed.”
Despite the geologic activity, the artifacts haven’t moved far from their original location. The deepest deposits have been kept from human eyes for 9,000 years, dating back to a time when glacial ice was still retreating from eastern Canada.
