The mountain ranges, which are a portion of the Pacific Coast Ranges, are not particularly high – Mount Olympus is the greatest at 7,965 ft (2,428 m); however, the east hillsides start rising from Puget Sound, and the foreign hillsides are divided from the Pacific Ocean by the low-lying 20 to 35 km (12 to 22 mi) broad Pacific Ocean coastal plateau. The western hills have the most precipitation of any of the 48 contiguous regions. The majority of the hills are preserved by Olympic National Park and bordering areas of the Olympic National Forest.

The mountains are in western Washington, USA, and are divided into four regions: Clallam, Grays Harbor, Jefferson, and Mason. They are a component of the wider Pacific Border region, which is itself a portion of the greater Pacific Mountain System.

The Olympic Mountains have the appearance of a collection of steep-sided mountains flanked by densely wooded lowlands and cut by wide basins. They are bordered on 3 sides by water and are isolated from the Pacific by a 20 to 35 km (12 to 22 mi) broad coastal plain. The range's basic shape is almost round, or horseshoe-shaped, and the drainage system is concentric.

Rivers extend outwards from all directions. The significant streams are Satsop, Wynoochee, Humptulips, Quinault, Queets, Hoh, Bogachiel, Sol Duc (all flowing west into the Pacific Ocean; the Satsop and Wynoochee via the Chehalis River, and the Humptulips via Grays Harbor at the tongue of the Chehalis River), Lyre, Elwha, Dungeness (all water that flows north into the Strait of Juan de Fu (all flowing east into Hood Canal).