Utah's Thrust System
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SURVEY OTES Volume 32, Number 1 January 2000 Utah's Thrust System In order for you to continue receiving Survey Notes, and to assist us in tailoring our mailing list to your specific needs, PLEASE complete and return this form before the next issue of Survey Notes: Utah Geological Survey, P.O. Box 146100, Salt Lake City, UT 84114-6100. Name: _________________________ _ Title: ________________ __. 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Since these times of tight state budgets. July 1999 I have been Acting Director Photo by Thomas Chidsey. In this coming year, we will be mak of the UGS, and will continue to serve ing the changes necessary to guide us State of Utah in this role until a new Director is through tough financial times and Michael 0. Leavitt, Governor named by Kathleen Clarke, Executive lead us into the next century and mil Department of Natural Resources Director of the Department of Natural Kathleen Clarke, Executive Director lennium. First, we anticipate having Resources (DNR). At this time, the UGS Board a new director some time in 2000. Craig Nelson, Chair search for a new director has been Second, we are revisiting our pro Richard R. Kennedy Robert Robison temporarily suspended, as it has re E.H. Deedee O'Brien Charles Semborski cently become apparent that the UGS grams and functions to see how they C. William Berge D. Cary Smith fulfill our mission and the needs of David Terry (Trust Lands Administration-ex officio) is facing some budget issues that will UGS Staff require immediate action. For those the state of Utah. Third, we are look Administration and Support of you who don't know me, I've been ing at our sources of funding to iden Kimm Harty, Acting Director tify ways to complete our work using John Kingsley, Assoc. Director Deputy Director of the UGS since Daniel Kelly, Acct. Officer 1996. Before that I was the UGS existing, new, and different sources Cheryl Wakefield, Receptionist over the coming years. Cheryl Ostlund, Adrnin. Secretary Technical Reviewer and Program Linda Bennett, Accounting Tech. Manager of the Geologic Extension William Case, Computer Resources Geology is a critical factor, albeit a Sharon Wakefield, Computer Resources Service for a few years. And, even generally quiet component in every Michael Hylland, Tech. Reviewer prior to that I worked nine years in day life. Geology provides the basic Survey Notes Staff the Applied Geology Program of the Editor: Jim Stringfellow needs of energy, mineral, and water Editorial Staff: Vicky Clarke, Sharon Hamre UGS. resources and only takes center stage Cartographers: Patricia Speranza, James Parker, Lori Douglas As we settle into this "new millenni during "extreme" events or "not so Applied Geology Gary Christenson um," the DNR and the UGS, its stake subtle reminders" like landslides or William Lund, Barry Solomon, Janine Jarva, holders, board, managers, and em flood emergencies, or when "fault" Francis Ashland, Richard Giraud, Brenda Nguyen, Greg McDonald ployees are looking at the growing structures are found below planned Economic Geology David Tabet need for geologic services, the shrink buildings. A challenge to the agency Douglas Sprinkel, Robert Gloyn, is to cultivate advocates of geology Robert Blackett, Roger Bon, Thomas Chidsey, ing availability of funding, and the Bryce T. Tripp, J. Wallace Gwynn, resulting decisions that need to be and to step up efforts to more effec Craig Morgan, Jeff Quick, Kevin McClure tively show our citizens and our lead Carolyn Olsen made. As you read this, we are busy Geologic Mapping Grant Willis examining our agency's mission, the ers how important this science is, and Hellmut Doelling, Jon King, Bob Biek, importance of its programs to Utah will continue to be, in everyday life in Kent Brown, Michael Wright, Denise Laes society, its funding sources, and fu Utah. As geologists, we already Geologic Extension Services Sandra Eldredge Christine Wilkerson, Mage Yonetani, ture direction. Funding shortages, in know this, but many others do not. Patricia Stokes, Mark Milligan, Carl Ege, cluding falling mineral-lease revenues Our challenge is to work to see to it Chris Ditton Environmental Sciences Michael Lowe last year, remind us of how we must that they do. David Madsen, James Kirkland, Martha Hayden, Janae Wallace, Hugh Hurlow, Charles Bishop, Alison Corey, Basia Matyjasik, Survey Notes is published three times yearly by Utah Geological Survey. 1594 W. North Temple, Suite 311 o. Salt Lake City, John Porcher Utah 84116: (801) 537-3300. The UGS inventories the geologic resources of the state, identifies its geologic hazards, dissem inates information concerning Utah's geology, and advises policymakers on geologic issues. The UGS is a division of the De partment of Natural Resources. Single copies of Survey Notes are distributed free of charge to residents within the United States and Canada and reproduction is encouraged with recognition of source. ISSN 1061-7930 SURVEY NOTES 1 Knowledge of Utah Thrust System Pushes Forward by Grant C. Willis ver the past few decades, through improved dating and correla els has significantly refined our study of the geometry, tecton tion methods. In an active thrust sys knowledge of timing and the se O ic forces, and dating of thrust tem, coarse alluvium is shed from quence of events that formed the systems produced some of the most rapidly eroding mountains formed by Utah thrust system. exciting advances in geology. Utah the thrusted rock. In some cases, Sevier Thrust System has been at the center of some of this soon after deposition, the advancing work. This is a brief overview of the thrust plates override, fold, and fault The Sevier thrust system is a typical development and evolution of the these "synorogenic deposits." To un thrust system consisting of, from west Utah thrust system, synthesizing the ravel thrust history, it is essential to to east, a thrust belt, a foredeep basin, work of many geologists. accurately date these rocks. a forebulge, and a back-bulge basin. The thrust belt is the wedge of The western or Cordilleran thrust sys In Utah, geologists scoured many stacked thrust plates. In Utah, single tem extends from Mexico to Alaska, miles of outcrops searching for data plates are up to 50,000 feet thick and, and formed mostly in the Middle ble materials. They collected and when thrusted into thick stacks or Jurassic to early Tertiary (170 to 40 identified pollen, spores, and volcanic culminations, may have formed million years ago). It formed as dense ash, then correlated the samples with mountains similar in magnitude to oceanic crust beneath the Pacific well-dated strata elsewhere. They the modern Andes Mountains of Ocean (Farallon plate) converged also mapped the conglomerates, un South America. The tremendous load with, and slid beneath the more buoy conformities, and cross-cutting rela of the stacked plates depressed the ant continental crust of the North tionships, and matched conglomerate crust under and in front of the thrust American plate during a mountain clasts with the formations from which belt (visualize forcing down the end building episode called the Sevier they were derived.