The Mojave Desert has several ghost towns; the most significant are the gold-mining town of Oatman, Arizona, the silver/copper-mining town of Calico, California, and the old railroad depot of Kelso. Some of the other ghost towns are more modern, created when U.S. Route 66 (and the lesser-known U.S. Route 91) were abandoned in favor of the Interstates. The Mojave Desert is crossed by major highways Interstate 15, Interstate 40, U.S. Route 95, U.S. Route 395, California State Route 58, California State Route 14, California State Route 138 and California State Route 18