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. However, increased groundwater pumping for irrigation and urban development eventually caused the river to dry up, leading to the loss of much of its riparian habitat 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. Today, the Rillito is an ephemeral river that carries water only during floods or snowmelt. In the late 20th century, as a
flood control measure, many segments of the riverbanks were stabilized with
soil cement to reduce erosion and prevent overflow that could damage property. ==References==