Natural Resources, School of


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Nebraskaland (March 2021) 99(2): 46-53


Copyright 2021, Nebraskaland Magazine, Nebraska Game and Parks Commission


Nestled in the hills of southern Jefferson County, Rock Glen Wildlife Management Area, as its name implies, is a rocky land shaped by ancient geological forces, among them, meandering tropical rivers and grinding glacial ice. Euro-American settlers in the region arrived to a picturesque scene: rolling hills cloaked in tallgrass prairie fingered by glens, narrow valleys and canyons, filled with sprawling bur oaks. Too rocky to plow, southern Jefferson County has survived as an island of prairie amidst a sea of cropland. Settlement was not kind to the land. Fire suppression allowed eastern red cedars and other trees to spread, choking the grasslands and oak woodlands and obscuring the ancient rock formations. Thanks to decades of recent work, however, the native plant communities have been restored, and the landscape is once again scenic.

Bob Diffendal, retired professor and research geologist with the University of Nebraska-Lincoln, is an expert on the geology of Jefferson County. Pick a pebble from the ground and he can name the rock type and its source of origin, ancient seabed, river channel or glacier. For a portion of his career, he studied the Dakota Formation, the heart of this rocky landscape. The Dakota, composed mainly of sandstone interspersed with shale, forms the surface bedrock of the region. On hillsides and flat ridge tops, it is veiled by a thin, mostly sandy topsoil, but is visible as boulders, shelves and cliffs in ravines and canyons. Diffendal explained that the formation was deposited in the Cretaceous Period more than 100 million years ago, when Nebraska had a tropical climate. Dinosaurs ruled the land while giant reptiles swam in the seas and flowering plants were just coming into their own. The North American Western Interior Seaway covered much of the continent. The sea stretched from the Rocky Mountains to eastern Nebraska, and from the Arctic Ocean to the Gulf of Mexico.