Northern Clackamas County is part of the rapidly growing Portland metropolitan area. Population of this 250-square-mile area increased about 50 percent between 1970 and 1976. The study area includes a small segment of the Willamette River alluvial valley near Canby, and extends northward to the Clackamas River and eastward to the western boundary of Mount Hood National Forest. Also included is the narrow, well-populated corridor along U.S. Highway 26 from Cherryville to Government Camp.
The main part of the study area is largely a rolling upland underlain by volcanic and stream-deposited rocks ranging in age from Eocene to Holocene. In most places, these rocks yield water in quantities adequate for individual homes. Locally, ground-water supplies are adequate for small irrigation, industrial, or public-supply uses. Depths of wells range from 50 to 1,000 feet; wells generally are shallowest in lowlands near streams and deepest in upland locations near deeply incised stream valleys.
All aquifers receive recharge at sufficient rates to sustain present rates of natural and man-produced discharge. All aquifers could supply additional water, but careful engineering is needed to avoid overdevelopment problems for the Columbia River Basalt Group near Oregon City.
Chemical analyses indicate that the ground water in the study area is of good quality for drinking and other uses. Mineralized water reported from some wells northeast of Canby may be from rocks of the Skamania Volcanics, which locally are at shallow depth. Although ground water locally may be subject to bacterial contamination where it occurs at shallow depths in alluvium and other unconsolidated deposits, no contaminated water was identified during the study.
