First off, this is my first post the the forums. Yay!
Right. So, I loved Earthcore. Very compelling story and I can't wait to hear about what happens next!
That said, as a life-long resident of Salt Lake City, there were a few details relating to Utah specifically, particularly in the first half of the book, that pulled me out of the narrative. Just a few things that didn't ring true to people familiar with the area.
The thing that was the most troublesome was the role of Brigham Young University and New World archaeology. Forgive me while I go into Mormon theology for a bit. I promise there is a reason. :) BYU is an arm fo the LDS Chruch. The LDS Chruch believes that there was a thriving civilization in the Americas, descended from Middle Eastern settlers, for thousands of years. The Book of Mormon mentions chariots, steel weapons, and all manner of other things that that a thriving bronze-age or later civilization would have.
Of course, there is no archaeological evidence for any of it. That's why the archaeological efforts, at least those focused on the Americas, is obsessively searching for any tiny scrap of evidence that might back up their theology. With that in mind, an ancient knife made out of steel or platinum would not be left half-forgotten in a store room, but would be heavily analyzed, lauded publicly by the LDS Church as one of the most important archaeological finds in history, and led to an immediate archaeological dig at the site.
It'd be really easy to resolve this by just setting the archaeology stuff at the University of Utah, which as alum of the anthropology program I can assure you would have no such dogmatic hangups. :) Of course, it might ALSO be interesting to hear about a team of BYU researchers who go on an expedition, only to disappear mysteriously.