Woodstock organizer Michael Lang had wanted Roy Rogers to conclude his now-iconic festival with a performance of “Happy Trails.” (Needless to say, Rogers declined.) But that’s far from the strangest thing about Woodstock.

Consider the festival’s penultimate act, presented at 7:30 on Monday morning, August 18. Sandwiched between the Paul Butterfield Blues Band (at 6) and Jimi Hendrix (at 9) was – Sha Na Na??!!

What was a fifties tribute band doing at Woodstock? A lot of caffeine, apparently (at best).

There at the request of Hendrix, all that gold lamé must have confused a lot of hippies.

The group’s high-energy performance of “At the Hop” makes it sound like a proto-punk anthem. Their instant notoriety kicked off or tapped into a tsunami of fifties nostalgia that left in its wake “American Graffitti,” “Grease,” “Happy Days,” and the band’s own syndicated variety show. Not too shabby, considering “At the Hop” was only 12 years-old.

Woodstock commenced with Richie Havens at 5:07 p.m. EDT, 50 years ago today. (Sweetwater, the group originally scheduled to open the festival, was delayed by the police.)

Grease for peace!