The total area of Mason County is 1,051 square miles, with 961 square miles of land and 90 square miles of water. The salt water area includes portions of Puget Sound and Hood Canal. The Skokomish River, Hamma Hamma, Tahuya, and the east fork of the Satsop River constitute the major rivers in the county. Two hundred thirty beautiful lakes dot Mason County. The most popular are Lake Cushman, Mason Lake, Spencer Lake, Lake Limerick and Lake Isabella.
Earthen dams are commonplace in Mason County.
The Lake Cushman hydroelectric project has two large, concrete dams supporting the Tacoma Public Utilities power plants at Lake Cushman and near Hoodsport. Elevations range from sea level to 6,000 feet in the majestic Olympic Mountains. Much of the native vegetation constists of conifers and evergreen shrubs. Soil conditions include wetlands, and fertile delta-like farmlands of the Skokomish Valley, rocky mountainous conditions, and poor soils with varying porportions of sand, gravel, loam, and clay. The average yearly rainfall is 64 inches.