1. a gorge of the Colorado River in N Arizona, extending from its junction with the Little Colorado River to Lake Mead; cut by vertical river erosion through the multicoloured strata of a high plateau; partly contained in the Grand Canyon National Park, covering 2610 sq km (1008 sq miles). Length: 451 km (280 miles). Width: 6 km (4 miles) to 29 km (18 miles). Greatest depth: over 1.5 km (1 mile)