An Urban National Park Oxon Cove and Oxon Hill Farm National Park - (shot on assignment for National Parks Magazine.) Oxon Cove and Oxon Hill Farm National Park sits on the southern border between Washington D.C. and Maryland. It hosts one of the oldest continuously functioning farms in the United States, as well as one of the only wild accesses to the Potomac river in the metro DC area. Being an urban park, however, this small corner of nature is under constant threat from city sprawl, development and pollution. But for many children born and raised in the city, it remains an easily accessible area to learn about nature, and interact with animals.