Four 33-cent Xtreme Sports commemorative stamps were issued on June 25, 1999, in San Francisco, California. The stamps are designed by Carl Herrman of Laguna Niguel, California, and photographed by the following: J. Grant Brittain, skateboarding; Keith Mulligan, BMX biking; Scott Spiker, snowboarding; and Mike Powell/Allsport USA., Inc., in-line skating. These stamps were intended to acknowledge the rapid growth and interest in Xtreme sports in the United States. The activities in this stamp set represent four sports with uniquely American origins. Each athlete is shown with safety gear appropriate to his or her sport. These visually exciting stamp designs are based on photographs that have been digitally altered and enhanced by computer.