Work began on the 1:250,000-scale geologic map of Washington in 1982. Previous quadrangles were published in 1987 (southwest), 1991 (northeast), and 1997 (southeast). The northwest quadrant represents the culmination of the first state map of Washington since 1961. This quadrant contains some of the most complex geology in the state, including rocks of the Northwest Cascades system, Olympic Mountains subduction complex, and the San Juan archipelago, as well as deposits of multiple incursions of Cordilleran ice sheets into the Puget Sound lowlands and the Straits of Juan de Fuca. This map is the first of the quadrants to be prepared by digital methods, and all of the source mapping is available digitally at a scale of 1:100,000.