Dead & Company was basically born last year, when John Mayer was filling in as the host of CBS’ “The Late Late Show” and The Grateful Dead’s Bob Weir was a guest.

They were supposed to play a couple of songs together on the show and ended up jamming for an hour and a half at sound check.

“I had never experienced anything like that musically, where I floated in that particular place in the sound of the band,” Mayer said in a recent conference call. “When we got in the room together with Billy and Mickey [the Dead’s drummers, Kreutzmann and Hart], for me, the idea just took hold of me when I heard it. And it was as big and strong as any idea I’ve ever had in my life.”

That idea became a new band — with guitarist Mayer, bassist Oteil Burbridge and keyboardist Jeff Chimenti joining three of the Grateful Dead’s “core four” (Weir, Hart and Kreutzmann) — and a new stadium tour, stopping at Citi Field on June 25 and 26, following an epic, 3 1⁄2-hour headlining set at Bonnaroo earlier this month.

Weir said the resulting band has been excited to “chase this muse.”

“We’re basically a couple of 14-year-olds looking at this immense palette of colors to paint with and in awe of the possibilities,” he said.

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“It’s just this wild, sort of reckless abandon,” added Mayer, who put recording of his new solo record on hold last year to join the band full-time and learn 100 or so songs from the Dead’s vast catalog.

“Interestingly for me now, the solo artist label is underneath the top of the pyramid, and the top of the pyramid is just musician,” said Mayer, who expects to finish his new album this year following the tour. “That is so freeing and beautiful. I’m not held to any record cycle.”

Mayer said he expects the Dead & Company collaboration to continue, maybe even expanding to new music.

“I would actually be very interested to see what the band could do as composers and as improvisers,” Mayer said. “But I’m open to anything that this band could or wanted to do as long as it answered sort of the constant question ‘Well, why?’ And if it has a strong answer, I would love to do it.”

“Using John’s imagery,” Weir added, “I’ll just say that I think it’s fertile ground.”