The Lathrop gas field is near the city of Stockton at the northern extremity of the San Joaquin basin in the area known as the Manteca arch. Continental Pliocene-Miocene strata unconformably overlie a thick series of Upper Cretaceous clastic rocks of mid-valley facies at Lathrop. The Stockton fault, a large cross-valley reverse fault with a complex structural history, nearly intersects the field's north limit.

Natural gas is trapped primarily in sandstone of Upper Cretaceous E Zone age because of anticlinal folding. Shallow drilling on the Lathrop fold dates back to 1937. Discovery of gas occurred 26 years later in October 1961 with the completion of Occidental Petroleum's Lathrop Unit A 1 for an initial rate of 13,550 Mcf a day. Nine distinct E Zone reservoirs are found at Lathrop, separated by thin bounding shale beds. The "3,700 Pound" Zone is the most extensive reservoir and has a productive closure of 2,400 acres with up to 600 ft of relief and gas-phase pressure continuity over 550 ft of section.

Thirteen dual-zone and seven single-zone wells have been completed for initial flow rates of up to 42,000 Mcf a day per well. Individual wells penetrate up to 600 ft of net pay. Deliveries of gas began in January 1963 and averaged approximately 50,000 Mcf a day for 1963. Independent volumetric reserve estimates have ranged from 578 million to more than 700 million Mcf.