tributary

In general use, a tributary is a stream that flows into a river or a lake. For instance, the important Colorado river has many tributaries, such as the Little Colorado River, San Juan River, Santa Cruz River, and the San Pedro River. However, in Tony Hillerman's 1970 Navajo detective novel THE BLESSING WAY, the characters travel through a canyon system which includes smaller canyons (tributaries) branching off from a larger one.