Rillito River
Dry riverbed near Dodge Blvd
Etymology	Spanish word meaning "Little River"
Location
Country	United States
State	Arizona
City	Tucson, Arizona
Physical characteristics
Source	Confluence of North and South Forks
• location	Pima County, Arizona
• coordinates	32°16′7″N 110°52′31″W / 32.26861°N 110.87528°W / 32.26861; -110.87528[1]
Mouth	Santa Cruz River
• location	Pima County, Arizona
• coordinates	32°18′49″N 111°3′18″W / 32.31361°N 111.05500°W / 32.31361; -111.05500[1]
• elevation	2,195 ft (669 m)
Length	12.2 mi (19.6 km)
Basin features
Tributaries
• left	Tanque Verde Creek
• right	Pantano Wash

The Rillito River (Spanish pronunciation: [ˈriʝito]; Spanish "Little River") is a river in Pima County, Arizona. It flows from east to west across the northern boundary of the City of Tucson from the confluence of Tanque Verde Creek and Pantano Wash to the Santa Cruz River 12.2 miles (19.6 km) away.^[2] The Rillito River Park runs along the north and south banks of the river from Interstate 10 to North Craycroft Road.^[3]

History

Prior to colonization by European settlers, much of the Santa Cruz valley was filled with riparian habitats, including numerous zones along the banks of the Rillito River. As recently as the late 19th century, the river was a perennial stream lined with trees and dense vegetation such as cottonwoods, willows, and mesquites.^[4] However, due to increased pumping of groundwater for irrigation projects to support agriculture and urban development, the river eventually dried up and much of the riparian habitat was lost by the mid-20th century. The loss of vegetation led to increased erosion of the river banks during flood events, which in turn led to a widening and straightening of the river channel.^[4]

Today, the Rillito is an ephemeral river that carries water only during floods or in response to snowmelt. In the late 20th century, as a flood control measure, many segments of the channel's banks were stabilized using soil cement to reduce erosion and prevent the water from overflowing the banks and damaging property.^[4]