Complex sentence: The Central City/Black Hawk Historic District is a federally designated United States National Historic Landmark that comprises Central City and the City of Black Hawk, adjacent former gold mining camps in the Front Range of the Rocky Mountains in Gilpin County, Colorado, United States.
Split into simpler sentences: The Central City/Black Hawk Historic District is a National Historic Landmark District that covers Central City and Black Hawk. They are adjacent former gold mining camps in the Front Range of the Rocky Mountains in Gilpin County, Colorado, United States.