The Midway-Sunset Oil Field produces primarily from Neogene sands and gravels which are found within the upper Monterey Formation, the Reef Ridge Shale, the Etchegoin Formation, the San Joaquin Formation and the lower and middle Tulare Formation. Age dates based on radiometric and paleontological analyses suggest that these producing horizons range in age from about 8.9 Ma (late early Mohnian) to about 1.0 Ma (Pleistocene).