Ruby Canyon is a roughly twenty-five-mile stretch of the Colorado River canyonland along the Colorado-Utah border in the western United States. Named for its ruby-red sandstone cliffs, it is a popular place for rafting and overnight camping, though camping requires permits. The canyon is also notable for its limited access: aside from traveling on the river, it can be reached only by the rail line between Mack, Colorado, and Westwater, Utah, formerly the Denver and Rio Grande Western Railroad. Amtrak’s California Zephyr also passes through the canyon, where travelers can spot the painted state line marker on the canyon wall near Utaline Siding.