Geology of the Snoqualmie Batholith (washingtonminerals.com)Snoqualmie Batholith - late Oligocene to early Miocene (28 Ma[million years ago] to 22 Ma). Uplift and erosion of the Old Cascade Volcanic Arc exposed plutonic rock of the Snoqualmie Batholith near Snoqualmie Pass between Interstate 90 and State Highway 2. The batholith consists of at least eight intrusive phases, emplaced at a depth of about 4,000 and 8,000 feet. Intrusive rock types found within the Snoqualmie Batholith range in composition from granite to gabbro. Granodiorite is the most prevalent rock type, making up about 80 percent the batholith (Erikson, 1969). Other lithologies within the batholith include porphyritic dacite, andesite, aplite, and intrusive breccia (Livingston, 1971).
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Skykomish River (Wikipedia)The Skykomish River is a 29-mile (47 km) long river in the U.S. state of Washington which drains the west side of the Cascade Mountains in the southeast section of Snohomish County and the northeast corner of King County. The river starts with the confluence of the North Fork Skykomish River and South Fork Skykomish River approximately one mile west of Index, then flowing northwesterly towards Puget Sound. It is joined by the Sultan River and the Wallace River at Sultan. It then meets the Snoqualmie River to form the Snohomish River at Monroe. The Snohomish River continues along the river valley eventually dumping into Port Gardner Bay on Possession Sound (part of Puget Sound).
