Abert Rim in Lake County, Oregon is one of the highest fault scarps in the United States. It rises 2,490 feet (760 m) above the valley floor, finishing with an 820-foot (250 m) sheer-sided basalt cap. It was formed during the Miocene epoch. At that time basaltic flood lavas covered much of eastern Oregon. In subsequent faulting, great blocks were tilted and Abert Rim is at the western end of one of these blocks, while Lake Abert lies on top of another. Stretching more than 30 miles (48 km) from Lakeview north to Alkali Lake, Abert Rim is also the longest exposed fault scarp in North America.