The Plateau Indians were those who lived within the broad region of highlands now called the Columbia Plateau. This area extended from west to east between the Cascade Mountains and the Rocky Mountains and north to south from the Fraser River in British Columbia down to northern Oregon and Idaho, with a small strip reaching into northern California.
Through this region flows the 1,200-mile-long Columbia River, in addition to innumerable rivers and streams fed by the drainoff from the flanking mountains. Tall coniferous trees grow in the mountains and river valleys, while the flat plains and rolling hills in between are covered with grasses and sagebrush.
The Plateau Indians lived by the seasons
The Plateau tribes went wherever they would find food most abundant. With access to very little big game but many rivers, they were primarily fishermen who supplemented their diets by hunting small game and by gathering roots, berries, and wild vegetables. In warm weather they built temporary, bulrush-mat-covered lodges alongside the rivers and on the plains. In cold weather they lived near the rivers in earth-covered, sunken pithouses.
Nations living in the eastern region of the Columbia Plateau (primarily the Nez Perce and Flathead (Salish) Indians) owned large herds of horses that they used to cross the Continental Divide to hunt buffalo in the Great Plains.
By contrast, the Indians in the western area were watermen whose main transport was the canoe, which they used to trade down to the coast. The rivers of the region, especially the Columbia, were a means not only of subsistence but also of trade and social intercourse among the Indians.
A huge trading network was centered around Celilo Falls and The Dalles, which teemed with Indians from numerous nations whenever the salmon were running.
There were two main language families, Sahaptian and Salishan, as well as other dialects.
The Corps of Discovery met many Sahaptian speakers among the Plateau tribes, including the Klickitat, the Nez Perce, the Palouse, the Tenino (Warm Springs), the Umatilla, the Walla Walla, the Wanapam, and the Yakama (Yakima).
Of the Salishan speakers, apparently only the Flathead had any interaction of note with the corps.
Other Salishans include the Coeur d’Alene (Skitswish), the Columbia, the Colville, the Kalispel, the Lake, the Shuswap, the Spokan, and the Wenatchee, among others. The Cayuse, the Klamath, the Modoc, the Kootenai, and the Stuwihamuk spoke different dialects, while the Chinookian-speaking Wishram are also grouped with the Plateau Indians.
The expedition’s dealings with the Plateau Indians they met were uniformly friendly.
Many of the nations had never before encountered white men; yet they greeted the explorers warmly, traded with them, shared food, and provided valuable assistance in the form of information or guides. When Meriwether Lewis characterized the Walla Walla as “the most hospitable, honest, and sincere people that we have met,” he could well have applied this description to many of the other Plateau Indians who helped to make the expedition a success.