Fens are a rare type of wetland found in the sandhill wetlands.
The sandhill wetlands are formed in depressions in sandhills areas where the groundwater intercepts the land's surface. The area is the largest contiguous tract of grassland remaining in the U.S. and also the largest stabilized sand dune area in the Western Hemisphere. The Sandhills encompass more than 19,000 square miles and overlie several groundwater aquifers of the Ogallala Formation. More than a million acres of lakes, marshes and wet meadows are present in the Sandhills. This Mylonchulus montanus female was recoved from a soil wash taken from the first 18 cm of a 2 m core sample.