PGS is Holding a Field Trip


Stanford University


  • Saturday & Sunday, Oct. 14-15, 1995
  • The trip: The focus of the trip will be the huge ( 6 by 19 km) serpentinite body in an extension of the Diablo Range, northwest of Coalinga. The serpentinite is in the core of a tectonically active antiform and contains one of the largest reserves of short-fiber chrysotile asbestos in North America. We will explore evidence for active tectonism affecting the serpentinite, visit the locality where a pure end member of jadeite was first discovered in North America, see one of perhaps two producing chrysotile asbestos mines in the U.S., and learn why the asbestos is causing a land-management dilemma for the U.S. Bureau of Land Management. Time permitting, we will visit an old mercury mine and inspect some of the Great Valley sequence that flanks the serpentinite.

    Leader: Bob Coleman, Prof. Emeritus, Stanford. Others who will provide expertise are Bob Jachens of the U.S. Geological Survey, who will help us understand the geophysics of the serpentinite, and Bob McLaughlin of the USGS, who will lend a hand in discussing the Great Valley sequence.

    Logistics: The trip will begin at a locked gate on State Highway 25 southwest of the serpentinite (see maps, below), where we will assemble 11:30 to 12:00 on Saturday. Allow about three hours driving time from the Bay Area to the starting point. We will camp that night at a private campground at an altitude of 4,500 ft. On Sunday we will work our way to the northwest, exiting the range on the highway to Panoche. Our plan is to arrive home in the early evening in time for dinner.

    Transportation: Colleges and universities should arrange transportation for their people. Those on the mid-Peninsula and at the USGS: Please contact John Galloway at USGS, (415) 329-5688, so we can arrange car-pooling. Use only vehicles with high clearance, such as pickup trucks, sport utility vehicles, or carryalls. Roads are too rough for sedans. People car-pooling from the USGS center in Menlo Park should meet at the flagpole on Homewood Place at 8:00 Saturday morning. Departure will be at 8:30.

    Food & equipment: Bring food for lunch and dinner on Saturday and breakfast and lunch on Sunday. If you need camping equipment, Mike Diggles, USGS, (650) 329-5404, may be able to help.

    Guidebook: Bob wrote this guidebook for the 14th General Meeting of the International Mineralogical Association that met at Stanford in July 1986. You can download a copy here.
    1986_Coleman_Field_Trip_Guide_to New_Idria_California.pdf

    Note: Bring water. No water is available at or near our campsite. Prepare for a cool night.

    Maps: Click on these maps for larger 9-kilobyte files.

    Dues for Academic Year 1995-96 ($5.00) should be sent to John Galloway, USGS, MS-904, 345 Middlefield Rd., Menlo Park, CA 94025. John's phone: 415-329-5688.

    Officers: Chet Wrucke, President; Mike Diggles, Vice President; Vicki Langenheim, Secretary; John Galloway, Treasurer

    Date created: 10/03/95
    Last modified: 01/30/2003
    Created by: Mike Diggles, Vice President, PGS.

    c/o U.S. Geological Survey, MS-901, 345 Middlefield Road, Menlo Park, CA 94025. (650) 329-5404 email to
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