pediment

A gently sloping, erosion-cut bedrock surface at the base of a mountain in an arid region, thinly veneered with sediment. Unlike a bajada (which is built up from deposited material), a pediment is carved down — the bedrock itself has been planed smooth by erosion. The distinction matters: a bajada is construction, a pediment is demolition. Both create the long, gradual slope between mountain and basin floor.