Big Four Mountain, Mountain summit in Snohomish County, Washington, United States.

Big Four Mountain is a summit in the Mount Baker-Snoqualmie National Forest in Snohomish County, Washington, known for its steep rock faces that rise sharply from the valley floor. Snow and ice collect at the base of those cliffs throughout the year, forming visible cave-like openings in the snowpack.

The Rucker Brothers built the Big Four Inn near the mountain's base in 1921; it burned down in 1949. The first recorded ascent of Big Four was made on July 19, 1931, by Forest Farr and Art Winder via the northwest ridge.

The ice caves at the base draw visitors who come to see the snow formations up close during summer months. The walk through the surrounding forest, with the bare rock walls looming ahead, gives a strong sense of contrast between the tree line and the open mountain face.

The trail to the snowfield is short and open to the public, but the snowfield itself is off-limits because of cave-ins and slides. Fatal accidents occurred there in 1998, 2010 and 2015. July through September offers the most favorable weather for viewing the peak.

The ice caves here are not formed by a glacier but by repeated avalanches that pile up massive amounts of snow each winter, leaving hollow spaces inside as the lower layers compress. This process explains why permanent snow survives at an elevation much lower than what is typical for glacier systems in the Pacific Northwest.