The Mogollon Rim is one of the longest escarpments on Earth; extending for over 200 miles (322 km) across central Arizona and reaching a height of 2000 ft. (610 m.), this imposing line of cliffs-- after the Grand Canyon-- is the second largest geologic feature in the state. It is of great geologic, biologic, hydrologic, and climatic significance. The Rim is a geologic boundary between the Colorado Plateau to the north and the Transition Ranges of central Arizona to the south. It forms the southwestern edge of the Colorado Plateau, a 130,000-square-mile (336,698-square-km) geologic province of mostly horizontal sedimentary rocks, vast plains, high mesas and buttes, deep canyons, volcanic fields and isolated mountain clusters. Weathering and erosion by running water are slowly wearing back the Rim to the north. South of the Rim are the highly faulted mountain ranges and intervening basins of the Transition Zone of central Arizona.