The Chuckanut Mountains were formed by the folding of the Chuckanut Formation (which is predominantly made up of layers of 55-million-year-old sandstone, conglomerate, shale, and bituminous and sub-bituminous coal) and the later Huntingdon Formation (predominantly shale and sandstone) on top, as well as an exposed section of pre-Jurassic-age phyllite- Rattlesnake Ridge (Wikipedia)
Rattlesnake Ridge, known as daʔšədabš to the Snoqualmie people, is the ridge of Rattlesnake Mountain located south of North Bend, Washington, United States. The western end is near the intersection of State Route 18 and I-90 in Snoqualmie, Washington, and runs southeast about 7 miles (11 km) or 11 miles (18 km) by trail. It is the highest and easternmost of the Issaquah Alps (although Cedar Butte in the gap between Rattlesnake Mountain and the Cascade front at Mount Washington is considered by Harvey Manning to be a quasi-Alp). A maze of abandoned logging roads and constructed trails have been strung together to provide a 10.5-mile (16.9 km) footpath from the Snoqualmie Point trailhead at Exit 27 on I-90 all the way to the Rattlesnake Lake trailhead near Exit 32.