According to local oral tradition, the Hohokam may be the ancestors of the historic Akimel O'odham and Tohono O'odham peoples in Southern Arizona. Recent work among the Sobaipuri, ancient ancestors of the modern Pima, indicates that Pima groups were present in this region at the end of the Hohokam sequence. The term Hohokam, borrowed from the Akimel O'odham, is used to define an archaeological culture that existed from the beginning of the current era to about the middle of the 15th century AD. As an abstract construct, this culture was centered on the middle Gila River and lower Salt River drainages, in what is known as the Phoenix basin. This is referred to as the Hohokam Core Area, as opposed to the Hohokam Peripheries; or adjacent regions into which the Hohokam Culture extended. Collectively, the Core and Peripheries formed what is referred to as the hoekam regional system, which occupied the northern or Upper Sonoran Desert in what is now Arizona.