Drillers have found a total of four oil pools in the Coalinga field. The first to be discovered was the Oil City pool of Cretaceous age, discovered in 1887 or 1888; however, it had little yield. On the east side of the field, along Anticline Ridge, the huge Temblor pool of Miocene age, at depths of 700 to , produced an enormous amount of oil in the early 20th century, and is now mostly exhausted. The other large pool is the Etchegoin-Temblor on the west side, of Pliocene-Miocene age, and at depths of 500 to ; this area is currently active and subject to enhanced recovery methods such as steam flooding, fire flooding, and water flooding, methods developed in recent decades in order to extract previously submarginal deposits.