This report is a brief description of the geology of the Solok quadrangle in West Sumatra. It is based on work done by the writer from April 27 to October 14, 1971, as part of the U. S. Geological Survey (USGS) Cooperative Project with the Geological Survey of Indonesia (GSI). The project is sponsored by the Government of Indonesia and the Agency for International Development, U. S. Department of State, and staffed by personnel of the USGS and counterparts of GSI.