The first discovery of oil in California was in Pico Canyon, on the north side of the mountains, The California Star Oil Works, later Chevron, succeeded with "Pico Well No. 4". It became famous not only as the first well in California, but also as the longest-producing well in the world, having been capped in September, 1990 after 114 years. Well No. 4 has the distinction of being the first site in Los Angeles County to be listed on the National Register of Historic Places, in 1966. The surrounding town, Mentryville, is maintained as the oil "ghost town" Mentryville Historical Park, within Pico Canyon Park. Many active oil and gas fields remain in the area, with some of the larger operators including Vintage Production, Freeport McMoRan, and the Southern California Gas Company. The largest of SoCalGas's four underground storage natural gas facilities is within the Aliso Canyon Oil Field north of Porter Ranch.