1. L. V. Benson, U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303, USA.
2. J. W. Burdett and R. O. Rye, U.S. Geological Survey, MS 963, Denver Federal Center, Lakewood, CO 80225, USA.
3. M. Kashgarian, Lawrence Livermore National Laboratory, Post Office Box 808, L-397, Livermore, CA 94550, USA.
4. S. P. Lund, Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA.
5. F. M. Phillips, Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.