Circular 163—Guidebook to Rio Grande rift in New Mexico

Compiled by J. W. Hawley, 1978, reprinted 1981, 241 pp., 4 tables, 156 figs., 2 sheets.

Discusses the details of geologic features along the rift zone. Included are short papers on topics relative to the overall region. These papers and the road logs are of special interest to any one pursuing further study of the rift. This book is a comprehensive guide to the middle and late Cenozoic geology of the Rio Grande region of Colorado and New Mexico. Though initially used on field trips for the International Symposium on Tectonics and Magmatism of the Rio Grande rift, the guidebook will be useful to anyone interested in the Cenozoic history of the 600-mi-long area extending from central Colorado to El Paso, Texas.

Sheets 1 and 2 show the region covered by the tour guide, including the route traversed and the location of stops. The book was organized to coordinate with field trips and technical sessions of the International Rift Symposium. Road logs into Santa Fe from both Denver and El Paso were planned to introduce participants to geological and geophysical features and concepts related to the geodynamics theme of the symposium.

The guidebook comprises five major sections. Three consist of road logs, with comprehensive entries at individual tour stops; a fourth section has three invited papers pertinent to the rift region as a whole, and the fifth section is made up of special maps, tables, and charts also related to various parts of the rift region. Two tectonic maps of the Colorado region and of the New Mexico-Texas-Chihuahua region are the basin illustrations for this guidebook and should be consulted during the tours.

The first two road log sections cover the routes to Santa Fe, New Mexico, southbound from Denver, Colorado, via Alamosa, and northbound from El Paso, Texas, via Socorro, New Mexico. Each section also contains a reverse route from Santa Fe to either Alamosa-Denver or Socorro–El Paso as well as a list of references cited. Road logs to Santa Fe contain complete tour text, including stop commentary, illustrations, and short technical papers pertinent to limited geographical features. Road logs from Santa Fe include only geologic and geomorphic features seen en route between formal stops; commentary is cross-referenced to the complete text and illustrations of the Santa Fe-bound logs.

Discussions at individual stops all relate to the central theme of rift dynamics in a geologic time frame covering the past 30 to 40 Ma. However, many discussions concern special themes, such as the Cenozoic evolution of individual range and basin blocks, case histories of local geophysical studies, or geomorphic expression of recent faulting.