It is thought that the Chuckanut Formation shoreline was of riverine environments combined with a large scale “bedding plane” of material deposition.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- The Chuckanut Mountains (from “Chuckanut”, an indigenous word meaning “long beach far from a narrow entrance”), or Chuckanuts, are located on the northern Washington state coast of the Salish Sea, just south of Bellingham, Washington. Being a part of the Cascade Range, they are the only place where the Cascades come west down to meet the sea. The Chuckanuts are considered to be a part of the Puget Lowland Forest Ecoregion.