East of Tucson, between the small towns of Benson and Willcox, Interstate 10 traverses a saddle between the Little Dragoon Mountains on the north side of the highway and the Dragoon Mountains to the south. This area, known as Texas Canyon, is famous for its spectacular boulder-strewn landscape. As the quartz monzonite boulders of Texas Canyon have weathered over time, they have tended to become increasingly rounded. This process of eroding and fragmenting rock is called exfoliation. Today, Interstate 10 follows the old stagecoach route of the Butterfield Overland Mail which operated here during the years just before the Civil War, allowing visitors to penetrate the heart of this fascinating area of gigantic rock outcrops.