aquifers is likely released as springs rather than reaching the aquifers. Studies of the chemical composition of groundwater at sites across the Grand Canyon region indicate that groundwater contains a fraction of modern water (post-1950), and that many springs have a mix of modern water and older groundwater. Estimated mean ages for South Rim groundwater range from 6 years old (San Francisco Peaks) to nearly 20,000 years old (Bar Four well, Blue Spring). Groundwater age in the South Rim groundwater system also correlates to longitude, with age increasing from east to west from Red Canyon to Boucher springs. Surprisingly, the Canyon Mine Observation well is more similar to Redwall-Muav aquifer wells (R-aquifer) than to the Coconino C-aquifer. This suggests the possibility of a hydrologic connection or similar recharge sources for that hydrologic position. Old groundwater from Havasupai well may have a similar source to the Havasu Spring upwelling from the Redwall-Muav aquifer. Sites with younger estimated mean ages tend to be associated with the unconfined Coconino aquifer. They may recharge quickly as a result of snowmelt, run-off and local precipitation. It is likely that the deeper confined R-aquifer relies primarily on snowmelt from the San Francisco Peaks to recharge. Other research has tried to relate groundwater flow paths to possible levels of risk for contamination and identify vulnerability regions for the underlying aquifers. Almost half of the Kaibab plateau's surface was associated with high to very high vulnerability of the unconfined Coconino aquifer (C-aquifer), while about a fifth of the Kaibab Plateau was estimated to be an area of high vulnerability for the Redwall-Muav aquifer (R-aquifer). History Native Americans The Ancestral Puebloans were a Native American culture centered on the present-day Four Corners area of the United States. They were the first people known to live in the Grand Canyon area. The cultural group has often been referred to in archaeology as the Anasazi, although the term is not preferred by the modern Puebloan peoples. The word "Anasazi" is Navajo for "enemy ancestors" or "alien ancestors". Archaeologists still debate when this distinct culture emerged. The current consensus, based on terminology defined by the Pecos Classification, suggests their emergence was around 1200 during the Basketmaker II Era. Beginning with the earliest explorations and excavations, researchers have believed that the Ancestral Puebloans are ancestors of the modern Pueblo peoples. In addition to the Ancestral Puebloans, a number of distinct cultures have inhabited