Wallula Gateway  (c. 1900, William Teakle Collection, Spokane Public Library). The mouth of the Walla Walla River is just above this often wind-blown gap where the Columbia River breaks through a ridge of layered basaltic rocks. In 1818 the North West Company built Fort Nez Perce (just upstream from here) to trade with native peoples along the Yakima, Walla Walla and Snake rivers. The location also served as a departure or arrival point for fur trapping brigades working the upper Snake River country. Today water levels on the Columbia River are higher due to McNary Dam, some 20 miles downstream.