Guidebook to Rio Grande Rift in New Mexico and Colorado 1978 Compiled by J
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Guidebook to Rio Grande rift in New Mexico and Colorado 1978 compiled by J. W. Hawley The Rio Grande rift is one of the more significant structural and topographic features of the earth. To understand its geologic history is to begin to understand the geologic history of the western United States—including the Rocky Mountains, the Colorado Plateau, the Basin and Range province, and the Great Plains. In addition, the geologic, topographic, geophysical, magmatic, tectonic, and geomorphic features of the Rio Grande rift are similar to those of other rift zones of the earth. Evaluation of these facets will contribute to knowledge of all rift zones and their relationships to worldwide tectonics. This guidebook is designed to acquaint those who take the field trips with the details of geologic features along the rift zone. In- cluded are short papers on topics relative to the overall region. These papers and the road logs are of special interest to anyone pursuing further study of the rift. In its own way, the guidebook is a symposium volume on the field features of the rift and is, therefore, a companion to the many papers presented at the symposium Rio Grande Rift: Tectonics and Magmatism to be published by the American Geophysical Union. As the New Mexico agency charged with the study of the state's geology and required to give scientific assistance in the exploration, development, and conservation of New Mexico's mineral wealth, we publish this guidebook to the landscape and geology of the heart of New Mexico—the Rio Grande rift. Many scientists have contributed their time and talents in the preparation of the road logs and articles, but major credit goes to John W. Hawley, who solicited papers and contributions, as- sembled the illustrations, wrote and rewrote most of the road logs, and who had full responsibility as compiler. The comprehensiveness and scientific excellence of this material are the result of John's efforts. Frank E. Kottlowski Director New Mexico Bureau of Mines and Mineral Resources GUIDEBOOK TO RIO GRANDE RIFT IN NEW MEXICO AND COLORADO And some rin up hill and down dale knapping the chucky stanes to pieces wi' hammers, like sae many road makers run daft. They say it is to see how the world was made. —Sir Walter Scott Circular 163 New Mexico Bureau of Mines & Mineral Resources A DIVISION OF NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY Guidebook to Rio Grande rift in New Mexico and Colorado compiled by J. W. Hawley in cooperation with 42 other coauthors prepared especially for Symposium on Tectonics and Magmatism of Rio Grande Rift Santa Fe, New Mexico, October 8-17, 1978 SOCORRO 1978 V Preface Many individuals and several organizations have assisted in compiling and editing this book. Early stages of work in 1977 were concerned with developing a guidebook concept that would best fit the International Symposium theme of Tectonics and magmatism of the Rio Grande rift. This effort included selection of tour-stop sites and routes of travel between Santa Fe and the starting points at Denver and E1 Paso. The following persons helped in this key phase of guidebook development: George Bachman, Elmer Baltz, Joe Bridwell, Chuck Chapin, Lindrith Cordell, Harold James, Wayne Lambert, Mike Machette, Kim Manley, Jacques Renault, Al Sanford, Glenn Scott, Bill Seager, and Ogden Tweto. Many of these persons have also contributed road-log and tour-stop entries. Information on formal contributions to the guidebook text, as well as names of individual contributors, is given in the Introduction. This assistance of 42 persons is gratefully acknowledged. In addition to the workers named above, the following individuals participated in the actual compilation and field checking of road-log and tour-stop entries: Roy Bailey, Richard Chamberlin, Ed Deal, Wolf Elston, Roy Foster, Ted Galusha, Vin Kelley, Frank Kottlowski, Bert Kudo, Pete Lipman, Bill Muehlberger, Bob Osburn, Jon Sandor, and Sam Thompson 1II. The final and somewhat hectic stage of guidebook compilation involved a team of staff members of the New Mexico Bureau of Mines and Mineral Resources. This included not only routine, high-quality stenographic and cartographic work, but also much round-the- clock effort by the Bureau editorial staff, particularly Candace Merillat and Joan Pendleton. There is literally no way that the book could have been published without their help. Special acknowledgment is due to Mike Inglis of the Technology Application Center, University of New Mexico, for assistance in selection of the Skylab photography used to illustrate this book. Photographs provided by the Technology Application Center and by Wayne Lambert, Bob Osburn, and Harold James are gratefully acknowledged. The Geological Society of America and the New Mexico Geological Society allowed the use of a number of illustrations from their publications. Finally, assistance rendered by the U.S. Geological Survey during the course of guidebook preparation deserves special acknowledgment. This help included preparation of the cover map, editorial assistance, and most of all, enthusiastic support for this publication effort on the part of many members of the Survey staff. John W. Hawley Environmental Geologist Socorro New Mexico Bureau of September 1, 1978 Mines and Mineral Resources Abstract 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 Española 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. PUBL1SHER'S NOTE to 2nd printing—In the scramble to get the original edition into print within a drastically foreshortened lead time ensuring that conferees would have copies in hand during the field tours, a couple dozen errors found their way into print. Most were inconsequential relative to the total effort. All have been corrected in the present edition. vi Contents [New Mexico Bureau Mines & Mineral Resources, Circular 163, 1978] vii [New Mexico Bureau Mines & Mineral Resources, Circular 163, 1978] v i i i FIGURES [New Mexico Bureau Mines & Mineral Resources, Circular 163, 1978] ix [New Mexico Bureau Mines & Mineral Resources, Circular 163, 1978] 11 Introduction This book is a comprehensive guide to the middle and late units include pre-rift rocks in blocks west of and within the Cenozoic geology of the Rio Grande region of Colorado and rift as well as rocks contemporaneous with rifting—such as New Mexico. Though initially used on field trips for the Inter- the extensive Pliocene basalt flows of the Taos Plateau. Con- national Symposium on Tectonics and Magmatism of the Rio tributors to the road logs and tour stops include R. H. Bur- Grande Rift, the guidebook will be useful to anyone interested roughs (pre-rift volcanics and structural evolution of the San in the Cenozoic history of the 600-mi-long area extending Luis Hills area south of Alamosa), P. W. Lipman (southeast- from central Colorado to E1 Paso, Texas. ern San Juan Mountains and the Taos Plateau west of the Rio Sheets 1 and 2 (in pocket) show the region covered by the Grande Gorge), and W. R. Muehlberger and John Hawley tour guide, including the route traversed and the location of (basin-fill stratigraphy and structure in the southeastern San stops. The book was organized to coordinate with field trips Luis Basin adjacent to the Sangre de Cristo and Picuris and technical sessions of the International Rift Symposium. Mountains). The northern rift guide concludes with road logs Road logs into Santa Fe from both Denver and E1 Paso (prior by Muehlberger and Hawley that cover the Rio Grande to formal technical sessions) were planned to introduce par- Canyon-Embudo constriction area (transitional between the ticipants to geological and geophysical features and concepts San Luis and Española Basins) and the eastern Española related to the geodynamics theme of the symposium. Basin. The guidebook comprises five major sections. Three consist Southern rift guides 1 and 2 highlight features of the rift of road logs, with comprehensive entries at individual tour between E1 Paso and Santa Fe. The southern road log has more stops; a fourth section has three invited papers pertinent to the parts than does the northern guide, because 1) the basic rift region as a whole, and the fifth section is made up of physiography of the region is characterized by many individual special maps, tables, and charts also related to various parts of (often isolated) range blocks and 2) the ongoing geological and the rift region. Two tectonic maps (sheets 1 and 2) of the geophysical research in the southern region represents the work Colorado region and of the New Mexico-Texas-Chihuahua of many different institutions and individuals. region are the basic illustrations for this guidebook and should The short Texas part of the tour offers a comprehensive be consulted during the tours. review of work on the Franklin Mountain block and the adja- The first two road log sections (Northern rift guides 1 and 2 cent bolson areas that extend from Texas and New Mexico in- and Southern rift guides 1 and 2) cover the routes to Santa Fe, to Chihuahua, Mexico.