Mount Si, Mountain summit in King County, United States.

Mount Si is a mountain in King County, Washington, rising above North Bend on the western edge of the Cascade Range. Its summit ridge is reached by the four-mile Mount Si Trail, which climbs 3,500 feet through dense forest. The final summit block, the Haystack, is an exposed class 3 scramble up its north side.

The mountain was named after Josiah Merritt, a local settler called Uncle Si, who made his home in the Snoqualmie Valley during the 1800s. This naming reflects how European newcomers left their mark on the landscape.

The Snoqualmie people connect this mountain to stories about sɬukʷalb, an important figure in their traditional beliefs. The peak holds a special place in how they understand the land around them.

The climb demands sturdy hiking boots, plenty of water, and generally takes four to six hours round trip. Plan to carry enough supplies and start early, as the trail is steady and offers few places to rest or resupply along the way.

The summit block is called the Haystack, reached by an exposed class 3 scramble on its north side. The mountain is a remnant of an oceanic plate volcano, and its rocks are a melange including metagabbro, Jurassic-Cretaceous in age.