Unit is named the Bellingham Bay Member (basal) of the Chuckanut Formation in the Bellingham Bay area in the western part of the largest outcrop belt of the Chuckanut, which extends from the San Juan Islands to the foothills of the North Cascades, WA. Consists of fining upward cycles of coarse-grained, cross-bedded, ripple-laminated sandstone and minor conglomerate intervals alternating with fine grained sandstone, mudstone, and minor coal intervals. A dacite lithic-tuff bed is near the top of the unit. Represents fine-load meandering river deposits in an extensive fluvial system. Unconformably overlies pre-Tertiary rocks; conformably underlies the Governors Point Member (new) and Padden Member (new), both of the Chuckanut, in the western part of the outcrop belt, and the Slide Member (new) of the Chuckanut, in the eastern part of the outcrop belt. Thickness is 2700 m along Bellingham Bay in the west and 3300 m in the east. Age is early Eocene based on zircon fission-track ages of about 55 Ma for the base and 49.9 Ma for the tuff at the top of the Bellingham Bay Member. (B1565)

Source: GNU records (USGS DDS-6; Menlo GNULEX).