Gray clouds carrying ocean moisture move inland from west to east and, when they strike the Cascade Mountains, rise, cool, and release heavy rain onto the fir forests of the west-facing slopes. East of the Cascade Range, skies are less cloudy and the plateaus are drier, with upland ponderosa pine woodlands descending to oak savannah and then to desert sage and grassland. The Columbia River Gorge is a meeting place of landscapes separated by the Cascade Mountains and contains five distinct vegetation zones, each adapted to local climate. In October 1805, near the present-day John Day River, William Clark observed high rugged hills with only scattered small pine or scrubby white oak where average annual rainfall was 14 inches. Near the present-day Klickitat River on October 29, 1805, he found the country on each side beginning to be more thickly timbered with pine and low white oak where average annual rainfall was 31 inches. Near present-day Cascade Locks on October 30, 1805, he recorded high mountains on each side thickly covered with spruce, pine, cedar, oak, and cottonwood where average annual rainfall was 36 inches.