While the Midway-Sunset field is a large contiguous area covering more than 30 sqmi , it comprises 22 identifiable and separately-named reservoirs in six geologic formations, ranging in age from the Pleistocene Tulare Formation (the most recent geologically, the closest to the surface, and the first to be discovered), to the Temblor Formation, of Miocene age (the oldest, and one of the last to be discovered).