This year’s performers include the Portland-based Shook Twins, a quartet featuring identical twins Katelyn and Laurie Shook. The group, a blend of folk and indie pop, produces alluring harmonies and is worth braving the heat. Other acts include The Honeycutters and Greensky Bluegrass on July 3 and Stokeswood and Donavon Frankenreiter on July 4. Fireworks show on both nights.