GEOLOGIC MAP OF THE GREATER PORTLAND METROPOLITAN AREA, OREGON AND WASHINGTON

We present a new geologic map of the greater Portland-Vancouver metro area, which occupies the tectonically active lowland between the Coast Range and Cascade volcanic arc. The map synthesizes the geology of 51 7.5’ quadrangles at 1:63,360 scale, including Paleogene marine strata of the Coast Ranges and their accreted basalt basement, somewhat younger rocks of the western Cascade arc, widespread flows of the Miocene Columbia River Basalt Group (CRBG), late Cenozoic fill of the Portland, Tualatin, and northern Willamette basins, including the Quaternary Boring volcanic field. Unconsolidated units, including extensive Missoula flood deposits and mega-landslide complexes are also mapped. We compiled the map in the USGS GeMS (Geologic Map Schema in ArcGIS) from digital sources at 1:24,000 scale; about 35% of which were previously unpublished. We locally reinterpreted published geology, resolved gaps and overlaps, and fixed mapping errors. Structure of the lowland is dominated by the NW-trending, Gales Creek and Portland Hills dextral-oblique fault systems that accommodate northward motion of the Cascadia forearc. The map provides an improved geologic framework for understanding of resources, hazards, and ecosystems, including: 1) earthquake hazards from crustal faulting and strong ground shaking, 2) aquifer storage and recovery systems in the CRBG, 3) natural gas storage in deltaic strata at Mist, 4) ecosystems along the Columbia River, and 5) the terroir of well-known northwest Oregon American Viticultural Areas.