This volume is a comprehensive field guide to the middle and late Cenozoic geology of the Rio Grande rift region extending from central Colorado south to the international boundary. Initially the book was used on field trips of the 1978 International Symposium on Tectonics and Magmatism of the Rio Grande Rift. Included are two multicolor tectonic maps (1:1,000,000) specially prepared for the symposium, one of Colorado and the other for the rift region of New Mexico, Texas, and Chihuahua. The road logs cover about 1,750 mi of a tour route from Denver to E1 Paso via Santa Fe. Logs are oriented for both northbound and southbound travel. Two additional logs cover the Jemez Mountain and Espanola Basin areas near Santa Fe. Detailed commentaries by 30 contributing authors on the geology and geophysics of 65 stops are included with the road logs. The volume also includes six invited papers on rift geology and geophysics, two correlation charts, selected data on deep drill holes in New Mexico, and heat-flow data for Colorado and New Mexico.