Landscape

The Missoula floods of the Pleistocene (2,580,000 to 11,700 years ago) transformed the Willamette Valley. “Floodwaters transformed the Willamette Valley into a lake 100 miles long, 60 miles wide, and 300 feet deep.” Eventually the water from the lake was drained into the Columbia River. Over thousands of years, this event was repeated hundreds of times and covered the valley floor with 15 feet of the soil carried from Washington, Idaho and Montana. The drainage of the Willamette River eventually included the rivers of the Cascade Range to the east, the Oregon Coast Range to the west and the Calapooya Mountains to the south making it at 11,487 square miles the largest watershed entirely contained within the state. It is also one of the 13 large river systems in the United States and has one of the second largest waterfalls by volume, Multnomah Falls at Oregon City. Beginning in 1900, the Army Corps of Engineers built 15 large and small dams along the Willamette and its tributaries primarily to produce hydroelectricity but also to create recreational reservoirs and prevent flooding (Figure 11).

The Willamette Valley's climate was, following the last glacial period, increasingly warmer. The valley floor was subject to periodic floods and was referred to as the valley of the tall grasses that included camas, fern and such various species of grass as willow, ash, hardhack, horsetails and members of the sedge family of grasses. The vegetation on the hillsides was dominated by lodgepole pine, spruce and fir. Western hemlock was also present in the foothills of the Coast and Cascade Ranges. Elk, deer, bear, coyote and cougar along with small animals still roam the hillsides that border the valley.

Community

Willamette Valley was the initial home of the diverse Kalapuyan groups that ranged from headwaters of the Willamette River to where it flowed into the Columbia. They lived in the hillsides along the river in separate villages often associated with Willamette River tributaries. During the warm months, they camped out with minimal cover but built stable plank houses for the cold months. They were hunters and gathers with a diet that included a diverse combination of animal (deer and elk) and vegetable (tarweed seeds, hazel nuts and acorns) resources.