The Olympic Mountains began about 35 million years ago as part of the ancient sea floor that thrust against the North American plate. Geologic forces fractured and folded these rock layers and lifted them high into the air, and erosion and glaciers carved the valleys and peaks visible today. Rising directly out of the Pacific Ocean on the west, the mountains reach their highest point at 7,969-foot Mount Olympus. The range is bordered by the Pacific Ocean to the west, the Strait of Juan de Fuca to the north, and Hood Canal and Puget Sound to the east. The mountains catch moisture-laden Pacific storms, bringing about twelve feet of rain each year to the west-facing valleys and sustaining temperate rain forest. At higher elevations, this precipitation falls as snow, adding to glaciers that continue carving the landscape. The east side lies in a rain shadow, with only 25 inches of annual rainfall and much drier conditions.