highest mountain (14,410 feet 【4,392 metres】) in the state of Washington, U.S., and in the Cascade Range. It lies about 40 miles (64 km) southeast of the city of Tacoma, within Mount Rainier National Park. The mountain, geologically young, was formed by successive lava flows from eruptions that began about one million years ago. The dormant volcano last erupted 150 to 175 years ago. Covering 100 square miles (260 square km), Rainier is surrounded by the largest single-mountain glacier system in the United States outside Alaska, with 41 glaciers radiating from the broad summit, including Nisqually Glacier, whose retreat and advance over the last 150 years has allowed scientists to determine patterns in the Earth's climate. The mountain contains three major peaks—Liberty Cap, Point Success, and Columbia Crest (the latter being the summit)—and is noted for dense stands of coniferous trees on lower slopes, scenic alpine meadows, waterfalls and lakes, and an abundance of wildlife and flowers.

The English explorer George Vancouver (Vancouver, George) sighted the summit on May 8, 1792, and named it for fellow navigator Peter Rainier. The first well-documented ascent was completed by Hazard Stevens and Philemon Van Trump on August 17, 1870. The mountain is now one of the country's premier destinations for climbers and is among the top venues for mountaineering training and instruction. Each year several thousand people attempt the climb to the summit, many of them on a guided two-day trip. Rainier is sometimes referred to by its Native American name, Mount Tacoma, or Tahoma.