Cumberland Mountains, part of the Appalachian Mountain system, extend across part of eastern Tennessee and Kentucky, and form the boundary between Virginia and Kentucky. Some geographers call this mountain region the Cumberland Plateau. Streams have carved a complex pattern of narrow, steep-sided valleys into the mountains. The Cumberlands rise from 2,000 to 3,000 feet (610 to 910 meters) above sea level. The mountains contain rich coal fields. See also Appalachian Mountains.