In its peak year of 1901, approximately 200 separate oil companies were active on the field, which is now entirely built over by dense residential and commercial development.

As of 2011 only one oil well remains active – behind a fence on South Mountain View Avenue one block east of Alvarado Street in the Westlake neighborhood, producing about 3.5 barrels per day (0.56 m3/d).

[2] Of the 1,250 wells once drilled on the field, and the forest of derricks that once covered the low hills north of Los Angeles from Elysian Park west, little above-ground trace remains.

Terrain in the vicinity of the Los Angeles City field includes gently rolling hills cut by ravines draining south.

Urban development is dense in the part of Los Angeles containing the field's former productive area, with numerous apartment blocks mixed with commercial and light industrial structures.

[6] An early assessment by Paul Prutzman (1913) rated the quality of the oil from the field as low, due to the high sulfur content and absence of light fractions suitable for refining.

Another early well, this one a failure, was dug to almost 400 feet (120 m) in 1865 near the intersection of Temple and Boylston, but the attempt was abandoned after encountering hydrogen sulfide gas from the oil deposits, which were not far below.

[9] More persistent drilling in 1890 by several groups of prospectors, including Maltman and Ruhland, succeeded in establishing production of several barrels of oil a day, and the California Department of Conservation credits these drillers with discovering the field.

They had dug a well to 155 feet (47 m), halting because of the accumulation of toxic hydrogen sulfide gas in the hole; however the oil seeps they encountered encouraged them to continue.

Doheny brought in a sharpened eucalyptus log and used it as an improvised percussion hammer to deepen the well, and shortly afterwards they punctured an oil reservoir, and began producing about seven barrels a day.

[11] While hardly a gusher, their first well at the corner of Colton and Patton Streets was in the middle of an area of hundreds of small town lots that had been sold in a land boom of 1887.

But it was still expanding: in 1896 a new well found oil east of the fault zone near Sisters Hospital which had previously been considered to be the eastern boundary of the field.

As her wells became successful, she shrewdly acquired others, forcing other operators out of business, and selling her oil to various local power companies, hotels, and utilities, all while doing her own accounting and continuing to give piano lessons at night.

[15] Edward A. Clampitt, an eastern businessman who had come to Los Angeles to make a fortune in the oil industry, was also one of the principal operators in the first decade of the 20th century.

[16] Production declined quickly after the peak; there were simply too many wells draining a reservoir of limited capacity and pressure, and less and less oil was able to be profitably extracted.

[17] 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.

Soil tests in the early 1990s showed methane at high levels, possibly migrating up from old wellbores (not all of which were mapped, let alone abandoned to modern standards).