The Aliso Canyon (Porter Ranch) is an Natural Gas Storage Cavern operated by Southern California Gas Company (SoCalGas).
There has been an underground leak to surface for several weeks.
Attached links with more info and infra-red video showing the plume of gas.
http://news.nationalpost.com/news/california-governor-declares-state-of-emergency-over-huge-gas-leak-in-los-angeles-neighbourhood
http://www.cbc.ca/news/world/california-natural-gas-methane-leak-sealed-1.3453850