LENOX — Joan Baez mentioned early on that she had recently visited the original site of Woodstock, the music festival she played while pregnant in August 1969.
“What a trip, man,” she said of going back there, adopting a far-out hippie accent that has never been part of her persona.
The past has always been alive for Baez, which is maybe why her set at Tanglewood on a muggy but sun-drenched day here was tinged with so much nostalgia on Sunday. She was already in familiar territory, too, sharing the bill with the Indigo Girls, who played Tanglewood with Baez in 1990.
Baez, who turned 72 this year, didn’t look back wistfully so much as she reassessed those halcyon days and gave thoughtful, often powerful renderings of some of her signature songs along with lesser-known material.
The potency of her earliest recordings — coiled tightly around Baez’s quaking soprano at the time — has given way to a more supple sound in recent years. Revisiting “Joe Hill” and “It’s All Over Now, Baby Blue,” she was at ease, her voice warm and unhurried, her phrasing the most nuanced it has ever been.
She’s traveling with a backing band that allows her to unfurl. Together with multi-instrumentalist Dirk Powell and her son, Gabe Harris, on percussion, they framed the songs in a loose Americana aesthetic that was nimble enough to accommodate folk standards (“Lily of the West”), country classics (“Long Black Veil”), and pop songs (“Imagine”).
It was astonishing to hear how Baez has grown into “The House of the Rising Sun,” turning it into a crawling acoustic blues lament, complete with a minor chord that Baez picked on her guitar to dissonant effect. “Swing Low, Sweet Chariot” — sung in honor of Baez’s mother, who died, at age 100, a few months ago — was similarly revelatory, a nearly a cappella rendition with Baez’s voice burrowing into her mid register and swooping to still-impressive heights.
More than 25 years into their career, the Indigo Girls are still emblematic of just how far hard work and solid musicianship can take you. Watching them on stage — and singing along at full volume to songs that hold up as classics (“Closer to Fine”) — you couldn’t help but sense they’ve become two trees that share the same roots. Amy Ray is the sturdy oak to Emily Saliers’s graceful willow.
Along with their band, they joined Baez for a closing set, rousing the crowd with “Don’t Think Twice, It’s All Right,” “The Water Is Wide,” and “Blowin’ in the Wind,” among others. They were songs that, like the afternoon’s performers, have stood the test of time.