This geologic map of the Ridgefield quadrangle shows Miocene lava flows of the Columbia River Basalt Group and younger sedimentary deposits in the northern part of the Portland Basin of southwestern Washington. The 13 geologic units are represented by colored polygons on the map. These polygons show the distribution of the rock units on the surface of the earth in this area. The map also contains 2 cross sections, a diagram that shows relative age correlation of the map units, an extensive description of those units and other symbols used on the map, and an index map. A more comprehensive description of the map units and other explanatory information can be found in the accompanying pamphlet. This map is one spatial representation of data contained in the accompanying database.