1. U.S. Geological Survey, Menlo Park, California 94025, USA
2. U.S. Geological Survey, Denver, Colorado 80225, USA
3. Nevada Bureau of Mines and Geology, Reno, Nevada 89557, USA
4. Department of Earth Sciences, University of Oregon, Eugene, Oregon 97403, USA
5. Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA