Oil well pumping unit, Half Moon Bay oil field, California

The Half Moon Bay oil field is one of the oldest oil fields in California and was first developed during the 1880s. Since then, the field has produced an estimated 60,000 barrels of oil from about 19 wells. Most of the old wells have been plugged and abandoned, but this well was reworked in 1980 and produces small volumes of oil from thin sandstone layers of the Miocene and Pliocene Purisima Formation at a depth of about 700 feet below the ground surface.