Los Alamos Canyon Creek, a stream or arroyo, tributary to San Mateo Creek, in the Cleveland National Forest in Riverside County, California. Its source is at an altitude of 2300 feet, in a canyon on the south face of the ridge of Elsinore Mountains that descends to the southeast from Elsinore Peak. The creek descends southward for a short distance then turns southwest for 4 miles where it turns west for 3 miles down Los Alamos Canyon to its confluence with San Mateo Creek at an elevation of 1312 feet.