Above the Levi’s Stadium, a plane makes repeated attempts to draw a peace sign with its vapour trail. Inside, one concourse has been given over to Participation Row, where stalls represent a motley collection of charities and pressure groups sanctioned by Dead members. At its furthest extreme the action is especially interesting, with representatives of MAPS – the Multidisciplinary Association For Psychedelic Studies, who advocate for the psychotherapeutic use of LSD and MDMA in treating life-threatening illnesses – positioned right next to the Owsley Stanley Foundation. “Bear” Stanley’s home-made acid fuelled the psychedelic revolution in San Francisco, but it is his work as the Dead’s soundman, and as someone who recorded over a thousand concerts by everyone from Miles Davis to Doc Watson, that the Foundation promotes, raising funds to digitally preserve his disintegrating tape archive.

On the field inside the Stadium, the amateur tapers have, as tradition dictates, a demarcated area for them to record the show. As Radiohead’s “House Of Cards” fades, however, and the seven-piece band amble on and slope into a loose, jazzy jam, even the most assiduous fans might be hard pressed to identify the song with which the Grateful Dead begin Fare Thee Well.

Five minutes in, a shape emerges. This is “Truckin'”, a chemically-enhanced road choogle from 1970’s American Beauty, and a rare anthem in a catalogue that is mostly too imaginative and devious to make such obvious moves. Bob Weir is singing Garcia’s old part, and while Anastasio is grinning so broadly that it seems he can barely believe his luck, his playing is commendably unostentatious. Much of the fancier work, in fact, is done by the two keyboardists: pianist Bruce Hornsby, who took time off from his solo career to become a floating Dead member in the early ’90s; and Chimenti, a longtime associate of Lesh and Weir, who is apparently playing Brent Mydland’s old Hammond B3.

“Truckin'” provides a gentle opening to a show that stretches over four and a half hours, including an hour-long interval, and features 17 songs – none of which were originally recorded any later than 1970. The first set gradually builds up speed, taking in a frail and lovely “Uncle John’s Band”, admittedly a little more Margaritaville than Wild West honky-tonk, before gaining momentum after 40 minutes with a wonderful “Cumberland Blues”.

There are beautifully-evoked flashbacks to the band’s dancehall roots, baroque psychedelic grooves like “Alligator” and “Born Cross-Eyed”. Perhaps best and most unexpected of all, Anastasio pilots a scything take on “Cream Puff War”, a rarity from their eponymous ’67 debut that’s been neglected by the band for the past 48 years and that, had it not been so thoroughly overshadowed by what came after, might now be regarded as a garage nugget to match Love’s “7 And 7 Is”.

At the climax of “Viola Lee Blues”, in the most elevating jam of the first half, and on the weekend that the United States legalise gay marriage, a perfect rainbow appears above the stage. It is all, perhaps, too good to be true.

 Heads up! Next month’s Uncut – on sale July 28 in the UK – comes with a FREE GRATEFUL DEAD CD: our historic attempt to piece together the album that should have followed “Workingman’s Dead” and “American Beauty”…