The Arroyo Willow is a small branching tree that can grow up to 30 feet. It has a smooth, light colored bark. This plant is extremely common at the St. Francis site, and grows in the riparian area, along the stream banks. It can also be found in the dry areas of the stream bed.
The small twigs of this tree contain salicylic acid, the ingredient in aspirin that are used to reduce pain and swelling. Twigs from these trees were used by the Native Americans for this purpose.