Agate is two stories in one park. The first is the fossils: some of the world’s finest Miocene mammal deposits, where early paleontologists pulled complete skeletons of animals known only from fragments — and where the spiral “Devil’s corkscrews” turned out to be the burrows of ancient land beavers. The 2.8-mile Fossil Hills and Daemonelix trails walk you through it.
The second story is the friendship between rancher James Cook and Chief Red Cloud, and it’s told through the Cook Collection of Lakota gifts and artifacts in the visitor center — one of the most respectfully presented Indigenous collections in the park system.
It’s free, open daily in summer with shorter winter hours, and 22 miles south of Harrison on Highway 29. Winter storms close the roads out here regularly, so check conditions before a cold-weather trip.