and the rivers, which are another below the White Rim. The Needles district is located south of the Island in the Sky, on the east side of the Colorado River. The district is named for the red and white banded rock pinnacles which are a major feature of the area. Various other naturally sculpted rock formations are also within this district, including grabens, potholes, and arches. Unlike Arches National Park, where many arches are accessible by short to moderate hikes, most of the arches in the Needles district lie in backcountry canyons, requiring long hikes or four-wheel drive trips to reach them. The Ancestral Puebloans inhabited this area and some of their stone and mud dwellings are well-preserved, although the items and tools they used were mostly removed by looters. The Ancestral Puebloans also created rock art in the form of petroglyphs, most notably on Newspaper Rock along the Needles access road. The Maze district is located west of the Colorado and Green rivers. The Maze is the least accessible section of the park, and one of the most remote and inaccessible areas of the United States. A geographically detached section of the park located north of the Maze district, Horseshoe Canyon contains panels of rock art made by hunter-gatherers from the Late Archaic Period (2000-1000 BC) pre-dating the Ancestral Puebloans. Originally called Barrier Canyon, Horseshoe's artifacts, dwellings, pictographs, and murals are some of the oldest in America. The images depicting horses date from after 1540 AD, when the Spanish reintroduced horses to America. Since the 1950s, scientists have been studying an area of completely surrounded by cliffs. The cliffs have prevented cattle from ever grazing on the area's of grassland. According to the scientists, the site may contain the largest undisturbed grassland in the Four Corners region. Studies have continued biannually since the mid-1990s. The area has been closed to the public since 1993 to maintain the nearly pristine environment. Wildlife Fauna Mammals that roam this park include black bears, coyotes, skunks, bats, elk, foxes, bobcats, badgers, ring-tailed cats, pronghorns, desert bighorn sheep, and cougars. Desert cottontails, kangaroo rats and mule deer are commonly seen by visitors. At least 273 species of birds inhabit the park. A variety of hawks and eagles are found, including the Cooper's hawk, the northern goshawk, the sharp-shinned hawk, the red-tailed hawk, the golden and bald eagles, the rough-legged hawk, the Swainson's hawk, and