Progress Report of New State Geologic Maps for Washington State

Nancy Joseph, Keith Stoffel, William Phillips

Geologic maps of Washington were previously published in 1936 and 1961 by predecessors to the Division of Geology and Earth Resources (DGER), Department of Natural Resources. These maps were printed at a scale of 1:500,000 and depicted the entire state on a single map sheet. The new state map will be at a scale of 1:250,000 and will be published as four quadrants with boundaries at 47°15^primeN latitude and 120°30^primeW longitude.

Compilation and original mapping for the four quadrants are being conducted at a scale of 1:100,000, using recently released U.S. Geological Survey metric 1:100,000 sheets as base maps. The 1:100,000-scale maps are reduced and simplified to produce final, 1:250,000-scale quadrant maps. The 1:100,000-scale geologic maps will be available to the public as DGER open-file reports.

The southwest-quadrant geologic map is the first of the series to be published, and is supported by 32 new K-Ar age determinations and approximately 200 geochemical analyses.

Preliminary 1:100,000 compilation maps of the northeast quadrant are complete. The 16 maps include new mapping or interpretations in the following areas: (1) Okanogan and Kettle domes, (2) Cambrian miogeoclinal and Ordovician eugeoclinal metasediments and metavolcanics of the Kootenay Arc, (3) southern segment of the Ross Lake fault zone, (4) Eocene volcanics in the Okanogan Range, (5) Eocene plutonic rocks near Republic, and (6) Quaternary sediments north of Spokane.

K-Ar age determinations, geochemical analyses, and conodont biostratigraphy are being used to refine the maps. Publication of the northeast quadrant is planned for late 1988.

AAPG Search and Discovery Article #91040©1987 AAPG Rocky Mountain Section Meeting, Boise, Idaho, September 13-16, 1987.