It's because it helps support the running and upkeep of the park, all GA State Parks are $5.00 a day or play it smart and get a yearly pass. If you become a supporter, you get free camping, shelter, and more, check that option out too
$5 for a park pass per vehicle per day. That covers one vehicle worth of passengers for the day. If you are staying in the park (i.e. camping at a camp site or renting a cottage) the $5 covers the extent of your entire stay.
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