SR 906 begins at a half-diamond interchange with I-90, exit 52, in Snoqualmie Pass, King County. North of I-90, Summit Road provides access to the Alpental ski area. Only the first of the highway is in King County, with the remainder of the highway in Kittitas County. After crossing the county line, SR 906 is bounded by Summit West on the west side of the highway and the Snoqualmie Pass Traveler's Rest rest area on the east side. Access to the Pacific Crest Trail is provided from the one of Summit West's parking lots. Just south of the rest area is an intersection with Yellowstone Road, which links back to I-90 at a full diamond interchange. Yellowstone Road was once a part of the Yellowstone Trail, a cross-country auto-trail.