Riparian communities are found along side perennial (annual) or ephemeral (seasonal) watercourses. On the Etiwanda Fan, small remnants of riparian are scattered on the upper slopes and canyons. The climate regime is the same as that for the surrounding communities with the exception of the moisture gradients afforded by the presence of the watercourse. Indicator species include Fremont Cottonwood (Populus fremontii), Western Sycamore (Platanus racemosa), a number of willow species (Salix spp.), and Mule Fat (Baccharis salicifolia). The largest tracts of riparian in the North Etiwanda Preserve are found within Day Canyon and Etiwanda Creek. Over-story components in Day Canyon and Etiwanda Creek vary and may include White Alder (Alnus rhombifolia), Canyon Live Oak (Quercus chrysolepis), numerous willow species and Western Sycamore. Under-story components frequently consist of Poison Oak (Toxicodendron diversilobum), California Wild Grape (Vitis californica), shade tolerant shrubs, ferns and non-native grasses.