1. U.S. Geological Survey, 2280 Woodale Drive, Mounds View, Minnesota 55112, U.S. Geological Survey, 2130 S.W. Fifth Avenue, Portland, Oregon 97201, U.S. Geological Survey, 3215 Marine Street, Suite E-127, Boulder, Colorado 80303, and U.S. Geological Survey, 8505 Research Way, Middleton, Wisconsin 53562