STRUCTURAL ANALYSIS AND CRBG STRATIGRAPHY OF THE PALOUSE FALLS AREA, EASTERN WASHINGTON

Fractures in the Palouse Falls area have greatly influenced erosion from the Missoula Floods, captured the Palouse River, and helped guide the recessional cataract that formed the majestic Palouse Falls. Origin of the fractures has been ascribed to folding and crustal lengthening, though conjugate angles are present in map view, suggesting lateral motion. If structures in the underlying basement resulted in fractures that penetrate through the Columbia River Basalt Group (CRBG), then the fractures may be a dominant influence on groundwater hydrology in an arid agricultural area. This study includes six stratigraphic controlled samples used for geochemical discrimination of the CRBG present in the Palouse Falls area. Whole rock analyses correspond to the presence of the Grande Ronde, Wanapum, and Saddle Mountain Formations in the project area. By measuring fractures from aerial photos and using fracture analysis we evaluate the hypotheses that fractures originated from 1) folding, 2) normal faults, or 3) transpressional structures. The orientation of the fractures correlates with other fracture zones within the State of Washington and regional geologic structures.