Well No. 4, Pico Canyon Oilfield, located about seven miles (11 km) west of Newhall, California, in the Santa Susana Mountains, was the first commercially successful oil well in the Western United States and is considered the birthplace of California's oil industry. Drilled in 1876, it turned nearby Newhall into a boomtown and also spawned a smaller boomtown called Mentryville adjacent to the drilling site. Well No. 4 continued in operation for 114 years until it was capped in 1990. The site was designated a National Historic Landmark in 1966, and the Mentryville ghost town is now open to the public as a historic park.