For the last several summers, writer and photographer David Hanson, a Georgia native gone west, has hiked a series of national parks with his father. As they’ve hiked, they’ve talked about the South, family, distance, fatherhood, baseball — and occasionally, a little politics. Last week, the U.S. National Park Service celebrated its 100th birthday. All who visit the parks look for what President Theodore Roosevelt called “the hidden spirit of the wilderness.” This story is about how that spirit moves inside one outdoorsman and his dad.