I missed the part between when Ed Harris' character, Mitch Wilkinson,
showed up Ben Gates' lectures to show that Gates' ancestor, Thomas
Gates, was a co-conspirator in the Lincoln assassination by providing
the missing page from Thomas Gate's diary and when Ben Gates arrived
at the conclusion that if the City of Gold was to be discovered,
Thomas Gates' name would be cleared up.
After the movie, my gf's nieces asked me how finding the City of Gold
was supposed to clear up Thomas Gates' name. I replied that since I
was in line to get them more popcorn for them, they should ask their
auntie.
But turns out, she had gone to the restroom while I was getting some
popcorn. So, I'm turning to this forum to see if anyone saw this
movie and can provide the answer to this. Thanks for your time and
courtesy.
The following links address the same question you ask.