The Topanga Canyon Formation () is a Miocene epoch geologic formation in the Santa Monica Mountains, Simi Hills, Santa Ana Mountains and San Joaquin Hills, in Los Angeles County, Ventura County, and Orange County, southern California. It is primarily composed of hard sandstone with some inter-bedded siltstone.
It preserves fossils dating back to the Miocene epoch of the Neogene period, during the Cenozoic Era.