A channel worn in the earth by a torrent of water carving out a deep ditch is called a gully. Gully erosion happens after a rill, a high-velocity rush of water, has removed large amounts of soil along a depression or drainage line. As water wears away the land, the rill—the geomorphic feature— becomes a gully; cutting farther down, the headlong water makes a gulch, until the cellar doors open into a canyon. On its smaller scale, gully erosion, or gullying, is the bane of farmers. It disrupts field operations, creates access problems for trucks and stocks, and uproots crops. Farmers learn to look for rabbit burrows, old root holes, cow or horse tracks on slopes, and lines of drainage, so they can stop gully erosion before it starts. But not everyone thinks of a gully as evidence of a necessarily destructive force. Sometimes the term is used to describe a placid waterway, as in this passage from Betty Zane, by Zane Grey: “Two hours of still-hunting found him on the bank of a shallow gully through which a brook went rippling and babbling over the mossy green stones.” Geographers distinguish between gullies, washes, and arroyos on the one hand, and cañadas on the other, according to the materials involved. Cañadas—like cañoncitos—slice through bedrock. Arroyos and washes cut through flat layers of valley deposits; and gullies and gulches erode hill-slope materials.

Elizabeth Cox