Danny Gatton, third from left, rests on an amplifier as David Chappell plays guitar at Jefferson Patterson Park in Calvert County, Md., in 1988. Also onstage, from left: Dave Elliott, Billy ...

The film “Anacostia Delta: Home of the World’s Great ‘Unknown’ Guitarists” promises to shed light on the lasting influence of guitarist Danny Gatton and the music of D.C. and Prince ...