Until the 1760s, the area that is now the city of Tracy was long populated by the Yokuts tribe of loosely associated bands of Native Americans and their ancestors. They lived on hunting and gathering foods, game and fish from the area, including its local rivers and creeks. After encountering the Spanish colonists, the Yokuts suffered from new infectious diseases, which caused social disruption, as did the Spanish efforts to impress them for labor at missions. Mexican and American explorers later came into the area, pushing the Yokuts out.