Lithology, thickness, and extent of hydrogeologic units underlying the East Portland area, Oregon

The lithology, thickness, and extent of eight distinct hydrogeologic units are described and mapped within the East Portland area of Oregon. The thickness, extent, and top of each unit are shown on contour maps at scales of 1:24,000. Their stratigraphic relations are displayed on a diagrammatic cross section. The geologic setting and unit lithology are described within the text. A data table presents information on each well or boring that was used for determining the thickness, extent, and lithology of each hydrogeologic unit. The hydrogeologic units range in age from late Miocene to Holocene and include several facies of the Troutdale Formation and Sandy River Mudstone, as well as Quaternary deposits of the Columbia River. From oldest to youngest, these units are referred to as: the sand and gravel aquifer, confining layer 2, Troutdale sandstone aquifer, confining layer 1, Unconsolidated gravel/Troutdale gravel aquifer, Columbia River sand aquifer, Blue Lake gravel aquifer, and overbank deposits. The total thickness of these sedimentary deposits is more than 1,300 ft in the sandy area. (USGS)