Colonial Peak, Mountain summit in North Cascades, Washington, US

Colonial Peak rises steeply from the southwest bank of Thunder Arm, an arm of Diablo Lake on the Skagit River. It climbs 6,560 feet (2,000 m) over just 2.3 horizontal miles, and its West Ridge is the standard climbing route.

The peak was first documented climbing by Seattle Mountaineers members in 1931. This early ascent established it as a recognized climbing destination in the North Cascades.

The name Colonial Peak comes from the Colonial mining claim on its slopes, a reminder of early prospecting in the Skagit valley. The claim predates the first ascent, which was made by William Degenhardt and Herbert Strandberg of the Seattle Mountaineers on July 31, 1931.

The standard route is the West Ridge, reached from Colonial Glacier. The approach follows the Pyramid Lake Trail, which starts near Diablo Dam on the North Cascades Highway. Snow on the peak is often wet and heavy, raising avalanche danger in winter.

Colonial Peak rises 6,560 feet (2,000 m) above Thunder Arm in only 2.3 horizontal miles (3.7 km), a steeper rise than its absolute elevation suggests. The standard route is the West Ridge, reached via Colonial Glacier and the Pyramid Lake Trail from near Diablo Dam.