The Green River Drift is 67.8 miles long, with 31.5 miles of spur trails. Each spring, ranchers from south of Hwy 351, east of Big Piney, bring their cattle north and are joined by other ranchers along the way to trail their cattle north into the Upper Green River Valley. In the fall, the process is reversed and the cattle come down from summer pasture out of the mountains to return to their home ranches. The Drift has been taking place each year since 1896.