I've been looking up info on known older burial sites in the area. I found two of interest.
- Japanese camp someone posted about earlier had a cemetery, but there are no records of it ever having been used. Remains were taken to another city and cremated.
- Native American burial ground named Nephi Mounds is one of only two in Utah, the other being nowhere near this area. I'm unsure how close/far Nephi Mounds is to the excavation site. It is in Juab County though, and I did find a map, so maybe someone better with maps than I, or who knows the area, could figure out how close it is.
Scroll down to the map. The Nephi Mounds are are in the lower left corner of the map:
http://tlc.howstuffworks.com/family/scenic-drive-in-utah-nebo-loop-scenic-byway-ga.htm
This site is where I found the official Native American burial grounds:
http://www.ibsgwatch.imagedjinn.com/learn/utah.htm
ETA: I meant to note that the Nephi Mounds were used in the 1300s.