[en] The U.S. Department of Energy, through the Basalt Waste Isolation Program within Rockwell Hanford Operations, is investigating the feasibility of terminal storage of radioactive waste in deep caverns constructed in the Columbia River Basalt. A portion of the geological work conducted in support of the Engineering Design Unit to evaluate the west end of Gable Mountain as a site for in situ testing of the thermomechanical behavior of basalt is reported. The surficial geology of the west end of Gable Mountain was mapped in a reconnaissance fashion at a scale of 1:62,500 to identify geologic features which could affect siting of the proposed facilities. A detailed study of the geological conditions was conducted along a traverse across the most probable site for the proposed project