The Capertee Valley is a large canyon in New South Wales, Australia, 135 km (84 mi) north-west of Sydney that is noted to be the second widest of any canyon in the world, exceeding The Grand Canyon. It is located 135 km (84 mi) kilometres north-west of Sydney, between Lithgow and Mudgee, in the Central Tablelands, just above the Blue Mountains.

A canyon, gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency to cut through underlying surfaces, eventually wearing away rock layers as sediments are removed downstream. A river bed will gradually reach a baseline elevation, which is the same elevation as the body of water into which the river drains. The processes of weathering and erosion will form canyons when the river's headwaters and estuary are at significantly different elevations, particularly through regions where softer rock layers are intermingled with harder layers more resistant to weathering.