The long and narrow San Joaquin Valley of California represents a Late Cretaceous to Pleistocene basin of deposition. Many sediment sources around the periphery have filled the basin with coarse clastic materials to a thickness of more than 40,000 ft (12,190 m). Numerous local and regional uplifts and structural deformations have combined with the varied depositional sources to create extreme structural and stratigraphic complexity. San Joaquin is the largest onshore basin in the state and contains 94 oil fields and 16 gas fields with proved reserves of 7.8 billion bbl of oil and 11.18 trillion cu ft of gas. I estimate that these proved reserves represent only 70 percent of the potential recoverable reserves of the basin. Of the 30 percent that remains, one fourth should e found in the north half of the basin. I estimate that the remaining three fourths will be distributed in the southern half of the basin in the following manner: "East Side," 5 percent; "South End," 5 percent; "Paloma Deep," 10 percent; "West Side," 10 percent; Bakersfield arch, 25 percent; and "Central Valley," 45 percent. Severe land problems plague the last three areas. Deeper drilling and a new exploration attitude will be required to find these additional reserves in stratigraphic and hidden structural traps.