Leschi Park erratic in Seattle’s Leschi Park is a sandstone erratic with many embedded bivalve fossils.
Analysis of the fossils and the rock’s minerals [of the Leschi Park erratic] shows it may have come from the Nooksack Group near Mount Baker, or from the Harrison Lake area of southern British Columbia.
https://github.com/davepinch/pinchy.cc/blob/master/content/topics/places/glacial-erratics/erratics/leschi-park-erratic/leschi-park-erratic.md