Cibola was an ancient Olmec City made completely out of gold. It was hidden in the rock that would later become Mount Rushmore in South Dakota. The final clues to its location was in the Book of Secrets. Benjamin Franklin Gates, along with friends and family, find the Treasure in Mount Rushmore in 2007.
The City's first clue was found in one of the what was John Wilkes Booth missing 18 pages of his dairy. That part of the diary was destroyed by Thomas Gates. Various clues from different places eventually lead to the Lost City of Gold and it is discovered that a former president created Mount Rushmore as a cover-up.