This abandoned line once formed the San Diego mainline of the California Southern Railway; it later became part of the Atchison, Topeka & Santa Fe transcontinental mainline.
The line was used up until 1927, when a number of washouts forced its abandonment in 1927. The land of the right-of-way was sold to the Temescal Water Company, which build Railroad Canyon Dam, completed in 1928, forming Railroad Canyon Reservoir, effectively submerging half of the length of the right-of-way.
Today, the right-of-way, split in two by the reservoir, can still be located. The northern portion can be followed from the Orange Empire Railway Museum, which was built along the old line, south to Railroad Canyon, right up to the water's edge. This portion of the right-of-way paralleled the San Jacinto River through an area called Railroad Canyon, is more visibly intact, but requires an off-road vehicle to access. The southern portion of the right-of-way can be seen from Railroad Canyon Dam to the line's connection with the Lake Elsinore Branch near present-day Mission Trail Road. Most of it parallels Railroad Canyon Road but is completely overgrown with trees or has been obliterated due to urban development.
Thanks to Andrew Bishop for contributing information about this route.