In 1973, a forty-year-old country musician named Willie Nelson, inspired by a failed music festival the year before, decided he was going to hold his own party. He would stage it in the same remote and rocky field where the previous festival had withered. And he’d do it in July: not the hottest part of the Central Texas summer, but “damn sure close enough,” according to music journalist Dave Dalton Thomas. As unlikely as it seemed in 1973, Willie kept the event going, minus a year off here...