Revealing mistake: In the scenes where Riley is using his computer to look up information on the "SearchInfo" site, the screenshot used is of Wikipedia. (You can even see the "About Wikipedia" link on the left).
Revealing mistake: When water is breaking through the wall you can see that at times the water is going through preformed squares.
Revealing mistake: In the scene where the barrels of beer are rolling off the truck, you can notice small squibs going off to make the barrels look like they have been shot.
Revealing mistake: When Nicolas Cage meets the president in the hangar and the president hands him a newspaper containing an article clearing Cage's great-great-grandfather's name, the text of the article in the center top of the newspaper in that scene contains the same body text as the article to the right that's titled "Family Saved."
Chosen answer: Because it verifies the story that the Gates family has passed down, that the pages were burned to protect the city of gold's location, not to hide his name as a plotter.
Boobra