Before the Grateful Dead formed, Jerry Garcia cut his teeth with a folk and bluegrass band called the Hart Valley Drifters. Garcia was just 20 years old when he played in the quintet, which featured Robert Hunter, with whom he would write many Grateful Dead numbers, and David Nelson, who went on to form the New Riders of the Purple Sage.

One day in 1962, the group recorded a session for Stanford University’s radio show “Folk Time” – the original tape was rediscovered in 2008 by Ted Claire, who recorded it that day. It’s now...