Structural Geology of the Mosier Creek Basin

A surficial and structural geologic map (SIR-2012-5002, fig. 2) was compiled to aid in the building of the three-dimensional geologic model. The map covers 327 square miles in north-central Oregon and south-central Washington, and completely contains the study area defined by the Mosier-Rock-Rowena Creek Watershed extents. Surficial and structural geologic maps, cross-sections, and stratigraphic interpretations of well logs from previous reports were synthesized into this compilation map (Newcomb, 1969; Swanson and others, 1981; Bela, 1982; Lite and Grondin, 1988; Kienle, 1995; and Jervey, 1996). The focus of this effort was to refine the geologic map within the study area to aid in construction of a three-dimensional geologic model to be used as the foundation for groundwater flow simulation. Areas outside of the study area boundary were given less attention.

The primary sources for surficial and structural geology were Lite and Grondin (1988) and Kienle (1995). Both extents together cover 78% of the geologic model area and represent the largest scales mapped. Individually each provides significant surficial and structural detail absent in other sources. Where they overlap both maps are mostly in agreement with only subtle differences. Both Lite and Grondin (1988) and Kienle (1995) together comprise all of the major structural components represented in the geologic model with the exception of the wrench fault associated with the Maupin trend.

Secondary sources for surficial and structural geology include Newcomb (1969), Swanson and others (1981), Bela (1982), and Jervey (1996). Newcomb (1969) was used to delineate alluvium, landslide deposits, glaciofluvial deposits, and Chenowith Formation material outside of the Lite and Grondin (1988) and Kienle (1995) map boundaries in Oregon. In the western portion of the map in Oregon and all of Washington, Bela (1982) was relied upon for surficial geology. Bela (1982) also provided all of the structural content outside the area covered by Lite and Grondin (1988) and Keinle (1995), with additional detail provided by Swanson and others (1981) and Jervey (1996).