Also, according to makoto niehe's comment on the 'Didn't Pan Out' achievement, the leftmost and rightmost three rocks are guaranteed not to have the jackpot, leaving the 6 in the middle two columns as the only places where the jackpot can be. When I tried this choice on the final jackpot, it actually worked and I got 5 attempts. According to AchieveSteve's guide, the 5-attempt pickaxe seems to always be the lightest colored one.

Now, you'll be going for the final jackpot, which is the highest one possible. Once there, keep spinning and wait for another Gold Rush to trigger and you'll be required to dig, as there are no more areas ahead of this. For each one you trigger, choose to move forward on the map instead of digging until you reach the red X. When you get three of the chariot icons with the words 'Gold Rush' on them within the screen, you'll trigger a Gold Rush.