The Olympics are made up of obducted clastic wedge material and oceanic crust. They are primarily Eocene sandstones, turbidites, and basaltic oceanic crust.Unlike the Cascades, the Olympic Mountains are not volcanic, and contain no native granite.The Olympics were shaped in the Pleistocene era by both alpine and continental glaciers advancing and retreating multiple times.- Olympic Mountains (Wikipedia)
The Olympic Mountains are a mountain range on the Olympic Peninsula of the Pacific Northwest of the United States. The mountains, part of the Pacific Coast Ranges, are not especially high – Mount Olympus is the highest summit at 7,980 ft (2,432 m); however, the eastern slopes rise precipitously out of Puget Sound from sea level, and the western slopes are separated from the Pacific Ocean by the low-lying 20 to 35 km (12 to 22 mi) wide Pacific Ocean coastal plain. These densely forested western slopes are the wettest place in the 48 contiguous states. Most of the mountains are protected within the bounds of Olympic National Park and adjoining segments of the Olympic National Forest.