Mount Rainier is the tallest mountain in Washington and the Cascade Range. This peak is located just east of Eatonville and just southeast of Seattle and Tacoma. Mount Rainier is ranked third of the 128 ultra-prominent mountain peaks of the United States. Mount Rainier has a topographic prominence of 13,210 ft (4,026 m), which is greater than that of K2, the world's second-tallest mountain, at 13,189 ft (4,020 m). On clear days it dominates the southeastern horizon in most of the Seattle-Tacoma metropolitan area to such an extent that locals sometimes refer to it simply as "the Mountain." On days of exceptional clarity, it can also be seen from as far away as Corvallis, Oregon, (at Marys Peak) and Victoria, British Columbia.
With 26 major glaciers and 36 sq mi (93 km2) of permanent snowfields and glaciers, Mount Rainier is the most heavily glaciated peak in the lower 48 states. The summit is topped by two volcanic craters, each more than 1,000 ft (300 m) in diameter, with the larger east crater overlapping the west crater. Geothermal heat from the volcano keeps areas of both crater rims free of snow and ice, and has formed the world's largest volcanic glacier cave network within the ice-filled craters, with nearly 2 mi (3.2 km) of passages. A small crater lake about 130 by 30 ft (39.6 by 9.1 m) in size and 16 ft (5 m) deep, the highest in North America with a surface elevation of 14,203 ft (4,329 m), occupies the lowest portion of the west crater below more than 100 ft (30 m) of ice and is accessible only via the caves.
The Carbon, Puyallup, Mowich, Nisqually, and Cowlitz Rivers begin at eponymous glaciers of Mount Rainier. The sources of the White River are Winthrop, Emmons, and Fryingpan Glaciers. The White, Carbon, and Mowich join the Puyallup River, which discharges into Commencement Bay at Tacoma; the Nisqually empties into Puget Sound east of Lacey; and the Cowlitz joins the Columbia River between Kelso and Longview.