Los Angeles City Oil Field, Los Angeles, California, United States

As the boom years of the field occurred before the formation of regulatory agencies in California, record keeping was sometimes sparse, not only for oil production but for the very existence and location of the wells. R.E. Crowder, writing in 1961, counted 142 wells which likely existed, but could not be located; some may have been dry holes. A more recent survey suggested that up to 300 wells may have been drilled within the vicinity of the oil field but abandoned without a trace.
By 1961 most of the oil field was dedicated to redevelopment as a residential area, under the auspices of the Los Angeles Urban Renewal Association. At this time, 93 wells still remained active in the field, run by 22 separate companies. One by one the wells have been abandoned, with the one remaining well quietly pumping behind a fence on South Mountain View Avenue.
• Recent land use controversies
After an explosion which leveled a Ross Dress for Less in the Fairfax District in 1985, caused by an overnight accumulation of methane which had seeped up from the underlying Salt Lake Oil Field, construction over Los Angeles's old oil fields became much more controversial and difficult. The city defined "methane zones" around all oil fields within its limits, and then enacted ordinances to ensure that new and existing structures within these zones were sufficiently ventilated to prevent the accumulation of explosive levels of methane. Mitigation systems for modern buildings include subsurface barriers, ventilation systems, methane detectors, and alarms. Thousands of buildings in the Los Angeles area have such systems, including the Staples Center and Los Angeles Convention Center.