1. U.S. Geological Survey, Columbia, South Carolina 29210, USA
2. U.S. Geological Survey, Lawrenceville, New Jersey 08648, USA
3. U.S. Geological Survey, Oklahoma City, Oklahoma 73116, USA
4. U.S. Geological Survey, Iowa City, Iowa 52240, USA
5. U.S. Geological Survey, Kearneysville, West Virginia 25430, USA