During the Pleistocene, sometime more recently than 1.8 million years ago, an enormous block of the Temblor Range - a swath of Monterey shale more than six miles (10 km) long, a mile across, and over thick, about three cubic miles of rock in all - slid down the northeastern side of the range, covering a distance of approximately three miles and descending . This mass movement completely covered the McKittrick Oil Field, giving it a highly unusual geology for an oil field, as the petroleum deposits in most oil fields are in structural or stratigraphic traps; this field is capped by an enormous mass of rock that moved off of the adjacent mountain range.