Landsat-4 Thematic Mapper (TM) imagery were enhanced and evaluated for geologic applications in both heavily and sparsely vegetated areas of the San Francisco Bay Region. False color composites of contrast-stretched spectral bands and principal component combinations were found to provide the most lithologic and structural information for geologic interpretation. The 30-m spatial resolution and seven spectral bands of the TM sensor were successfully used to delineate regional geobotanical anomalies, faults, and fractures in the heavily vegetated New Almaden area of the Santa Cruz mountains and regional lithology and structure of the sparsely vegetated Diablo Range. A number of these features have not been previously recognized using conventional aerial and field mapping techniques. Data reduction techniques employed to reduce the effects of band correlation assisted the geologic interpretation in the heavily vegetated areas but were of little use in the sparsely vegetated areas. This work demonstrates the ability of TM imagery to assist in the interpretation of lithologic, structural, and geobotanical features critical to deciphering a region's geology or mineral potential.