The acorns from oaks (Quercus) and tan oaks (Lithocarpus) have been used as food for many thousands of years. They occur in the archaeological record of the early town sites in the Zagros Mountains, at Catal Hüyük (6000 BC), and oak trees were carefully inventoried by the Assyrians during the reign of Sargon II. In Europe, Asia, North Africa, the Mid-East, and North America, acorns were once a staple food. They are still a commercial food crop in several countries. Acorns are still harvested and used in several areas of the United States, most notably Southern Arizona and California. There is still some harvesting in Mexico. For many of the native Californians, acorns made up half of the diet and the annual harvest probably exceeded the current sweet corn harvest in the state.