"But I'm not buying it."

The Grateful Dead, unlike most other bands, encouraged audience members to record concerts. Usually, there would be a special "taping section." But this concert was different. It was held in Kleinhans Music Hall, and orchestra rules generally forbade recording.

Still, Grateful Dead fans are a freewheeling bunch, and so hope springs eternal.

"I've heard of this great white whale recording for 40 years," Caputo wrote. "In my foggy memory of many years following the Dead, I even believed I listened to it in somebody's VW bus."

The absence of a recording is just one reason that this particular concert has, over the years, generated buzz. The concert was unplanned. Though Foss is often credited with conceiving the concert, it was actually spontaneous: The Dead were called in at the last minute to fill in for the Byrds, who had canceled.

The reviewers who attended the event gave tantalizing accounts of what went on.

"Orchestra’s Rapport With Rock Bands Electrifies Audience," read the headline in The News. Smaller headlines that followed throughout the story read: "Dueling Drummers," "Orchestra Divided," and "Effective Light Show."