Located 4 miles east of Afton in the Salt River Range, this is the largest of three natural springs in the world that naturally turn off and on. Water flow is interrupted for anywhere from 3 to 30 minutes, generally between the months of August and May. It is thought that a cave behind the spring creates a siphon that causes interruptions in the water flow. Its ability to turn off and on during low discharge stages has fascinated visitors since prehistoric times. Access to the spring is via Swift Creek Road and requires a 3/4 mile hike by trail.