Decker Canyon Creek and Morrell Canyon Creek, tributaries of San Juan Creek, and San Mateo Creek have their sources on the western face of the Elsinore Mountains. Los Alamos Canyon Creek, and its tributary Wildhorse Canyon Creek, tributaries of San Mateo Creek, drain its south facing slopes. The ephemeral streams on the eastern slopes drain into Lake Elsinore (tributary to the Santa Ana River), except on the far southeastern ridge, where they are tributary to Murrieta Creek, a tributary of the Santa Margarita River.