A Slice Through Time

A Slice Through Time. . The face of this cliff reveals a chronology of geologic events as well as clues about animals and habitat., Halfway up the cliff face are a series of vertical spiral shapes. First called "devil's corkscrews" (Daemonelix) by local ranchers, these sandstone spirals are burrows of ancient beavers (Palaeocastor). The spacing and number of burrows suggest that the animals lived in communities similar to those of modern prairie dogs. The top of each burrow marks the ground level when these beavers existed. Study of fossilized plant roots associated with these burrows suggests a habitat with abundant vegetation, including grassland, in the vicinity of wide shallow streams., The sandstone forming the cliff face was deposited over thousands of years as sediment filling an ancient Miocene valley. The present topography was sculpted by erosion of the Niobrara River., Captions , Upper Right: The corkscrew burrows are most visible during the late afternoon. This 1955 photograph shows several burrow locations on the cliff face. , Lower Right: Palaeocastor and burrow. The bottom of the corkscrew opens into a nesting chamber tilted upward to prevent the accumulation of water . This historical marker was erected by Agate Fossil Beds National Monument, National Park Service. It is in Agate in Sioux County Nebraska