If your search radius – that is: the distance between your Forrest Fenn Treasure Clue Number 1 and Clue 9 – is 500 feet, then your search area is .028 square miles, roughly 1/4 square mile or approximately 13.5 football fields¹.
If, on the other hand, your search radius is 10 miles, then your search area is a little over 314 square miles, or approximately 152,427 football fields.
But, let’s say you’re headed in a single direction inside your search radius – that is, you’re going to travel in, effectively, a straight line from clue 1 to 9. Then, in the case of your 500 foot search radius, you’ve reduced the problem to approximately 1.66 football fields. And, in the case of your 10 mile search radius, you’ve reduced the problem to approximately 176 football fields.
Good luck in your search.
¹Excluding end zones.