Geology and coal resources of the Centralia-Chehalis district, Washington (pubs.usgs.gov) The Centralia-Chehalis coal district includes about 570 square miles in south western Thurston County and northwestern Lewis County, Wash., midway between Seattle, Wash., and Portland, Oreg., and forms a part of the subbituminous and lignite coal fields of southwestern Washington. It adjoins the Morton coal field on the east and the Toledo coal field on the south. It includes a part of the extreme western foothills of the Cascade Range and a part of the eastern border of the Coast Ranges.