Named for the nearby rock formations containing agate, the fossil beds underlie the grassy Carnegie and University hills, which overlook the Niobrara River. The fossils are imbedded in the sedimentary rock formed some 20 million years ago.
The monument covers some 2700 acres and lies 23 miles south of Harrison on Highway 29. Picnicking is permitted, but the collecting of fossils, rocks or plants is forbidden.