Big Bend National Park encompasses more than 800,000 acres in southwest Texas and includes mountain, desert and river environments. It is open year-round and has national significance as one of the largest protected areas of Chihuahuan Desert topography and ecology in the United States. The 118 river miles that form the southern park boundary includes the canyons of Santa Elena, Mariscal and Boquillas, Texas. It offers a range of recreational opportunities, such as hiking, window-view trailing, bicycling, rock climbing, floating, bird viewing and stargazing. Big Bend National Park offers the Parks as Classrooms program, which is a nationwide initiative to utilize various resources of the park for teaching and learning purposes. It is located in Big Bend National Park, Texas, and is a part of National Park Service, which is a network of more than 400 natural, cultural and recreational sites throughout the U.S. It is a bureau within the Department of the Interior.