The Rillito River is a seasonal river located in Pima County, Arizona. It flows primarily through the city of Tucson and is a tributary of the Santa Cruz River. The river's flow is dependent on rainfall and snowmelt, often drying up during the hot summer months. The Rillito River is an important natural resource for the region, providing habitat for various wildlife species. It is also a popular recreational area, with trails for walking, biking, and horseback riding along its banks. The river's watershed plays a crucial role in the local ecosystem and water management.