We use geology as a proxy to produce a site condition map of mainland China for seismic hazard assessment. The geology is from a 1:1,000,000‐scale digital database and a 1:2,500,000‐scale Quaternary map. We use the lithological descriptions and ages to assign the site condition for each geologic unit. Published site condition data are used to evaluate our mapping results. Our results agree well for the strong‐motion stations in Gansu–Sichuan area, except in the mountainous area. There, the mismatches are due to our geological map scales missing narrow river terrace deposits. Our results also match well in the Shandong and Beijing Plain areas, except in thin fluvial and alluvial deposits fringing bedrock mountains. Our site‐response categories match well‐published average –depth profiles from microzonation studies of 14 major urban areas.