The Black Hills are in the southwestern part of South Dakota and extend into Wyoming. This range of low mountains covers , with peaks that rise from 2,000 to 4,000 feet (600 to 1,200 m) above their bases. The Black Hills are the location of Black Elk Peak (7,242 ft or 2,207 m above sea level), the highest point in South Dakota and also the highest point in the United States east of the Rocky Mountains. Two-billion-year-old Precambrian formations, the oldest rocks in the state, form the central core of the Black Hills. Formations from the Paleozoic Era form the outer ring of the Black Hills; these were created between roughly 540 and 250 million years ago. This area features rocks such as limestone, which were deposited here when the area formed the shoreline of an ancient inland sea.