 The East Fork of the Lewis River and the Washougal River cut across the county.The largest stream arising solely within the county is Salmon Creek, which terminates at Vancouver Lake before eventually flowing into the Columbia River.Like most of Oregon and Washington south of Puget Sound into the Willamette Valley the landscape and climate of Clark County are determined by its placement between the volcanic Pacific Coast and Cascade Ranges, where glaciation helped form a U-shaped valley which meets the river valley of the Columbia River as it leaves the Columbia River Gorge.