Some partnerships are built to last. Take Neil Young and Stephen Stills, who have been making music together for nearly 60 years, all the way back to their first band together, Buffalo Springfield.

On Saturday afternoon, they were together again headlining “Harvest Moon — a Gathering,” a benefit concert for the Painted Turtle camp in Lake Hughes for children with chronic illnesses, making music in the blazing sunshine an hour north of Los Angeles.

The grassy campus in Lake Hughes, founded in 1999 by a group led by actor Paul Newman and philanthropist Page Adler, was an idyllic setting for an eruption of classic rock and folk, with loud electric guitars and softer acoustic songs. Money was also raised for the Bridge School in Hillsborough, Calif., a favorite Young charity that serves children with severe speech and physical impairments. Hitmaker and jam band guitar virtuoso John Mayer also performed a short set.

Despite Young and Stills’ long association, the annual benefit for the Turtle Camp was a rare opportunity to see the two perform a full set together since the acrimonious hiatus of their storied supergroup Crosby, Stills, Nash and Young.

Young stepped out in a train engineer’s cap and shades, carrying a hollow-bodied Gretsch electric, harmonica firmly placed at his lips. Stills wore black, with a gray goatee, plucking an almost identical guitar.

After a moment of introductory feedback, they began with 1976’s “Long May You Run,” title song from their only release as a duo. As an opening, it was predictable and completely fitting, a song of warmth and brotherly friendship, both gentle and built to last, as Young sang: “We’ve been through some things together / With trunks of memories still to come / We found things to do in stormy weather / Long may you run.”

Stephen Stills, left, performs alongside Neil Young. The song choices were wide-ranging, with Young on his acoustic as much as electric during the hour-long set.

(Steve Appleford / For The Times)

The atmosphere at the Painted Turtle was like a weekend picnic, with 3,500 fans spread across the grass, in folding chairs up front, many standing in back. Behind the barn were food trucks and other amenities for donors and fans waiting for the show to begin.

Young is a famously restless rocker, with multiple projects and collaborators at all times, simultaneously looking backward with a curator’s touch and leaning forward with a steady stream of new music.

At age 78, he’s going strong performing with Crazy Horse, Promise of the Real or as a solo act. But he took an extended break from touring in the wake of the COVID-19 pandemic. He was in no rush to get back out there and to risk his health and that of his bandmates and fans.

That uncharacteristic silence ended last year with a series of celebrated solo performances at the Ford theater in L.A. Since then, Young has been fully back in action. But when a planned world tour this year with Crazy Horse was canceled because of an unspecified illness within the band, Young was sidelined once again. Not anymore.

Just a week ago at the Capitol Theatre in Port Chester, N.Y., Young introduced a new band he calls the Chrome Hearts, which includes some of the younger players he’s periodically collaborated with over the last several years, mostly under the name Promise of the Real.

The group’s rhythm section — bassist Corey McCormick and drummer Anthony LoGerfo — was beside Young on Saturday. With the formidable Stills in the house, no other guitarist was needed, with him acting as the foil Young often craves onstage.

John Mayer

(Steve Appleford / For The Times)

The song choices were wide-ranging, with Young on his acoustic as much as electric during the hour-long set. Young frequently drifted to Stills’ side of the stage to lock into a guitar wind-out with his old partner, with the eyes of one often locked on the playing fingers of the other.

Stills led on his 1970 solo hit “Love the One You’re With.” Stills also brought out “Hung Upside Down,” calling it a “new version” of the old Buffalo Springfield tune that he said dated back “two centuries.” He also sat at the piano as Young sang “Helpless,” one of Young’s most memorable and vulnerable CSNY songs. It was forlorn and wistful. When it was done, Stills gave Young two thumbs up.

Now 79, Stills hasn’t toured since 2015, although he periodically hosts his “Light Up the Blues to Benefit Autism” show, where Young has appeared with him in the past. This time, Stills was returning the favor, standing out in the sunshine to tap into the fire of their first band together, Buffalo Springfield, and the occasionally active CSNY.

While Young was inevitably the captain of this ship, the two veteran rockers stood as equals, playing each other’s tunes, as they have since the mid-1960s. With the death early last year of singer David Crosby (at age 81), any possibility that the members of CSNY might reconcile ended. Despite the loss of Crosby, the Stills-Young relationship has endured.

The band played Young’s gentle, romantic “Harvest Moon,” with LoGerfo on brushes. Beginning with “Heart of Gold,” Young was joined by a trio of background singers — opener Lily Meola and her two band members, Bre Kennedy and Eva Cassel — all dressed in white, swaying behind their mics.

Neil Young

(Steve Appleford / For The Times)

The number of Grateful Dead T-shirts in the crowd owed something to the presence of Mayer, who is now a journeyman associate of a revived version of the band, Dead and Company, and was onstage with the latter during its recent run of shows at the Sphere in Las Vegas. But his six-song set on acoustic guitar was focused on his hugely successful work as a solo artist, as fans called out for favorites from his catalog.

Mayer began with the romantic “Who Says” and “Something Like Olivia” and teased the crowd over song choices, suggesting that while the hardcore fanatics might have been right up front yelling for deep cuts, the listeners in back might prefer some hits. He was back onstage at the end of the Stills-Young set, joining as one more electric guitar gunslinger on “Rockin’ in the Free World.”

That song closed the night, after a final plea from Young about the cause of the day (“Don’t forget those kids”). The musicians cranked up the amplifiers, and Stills sang a verse of Young’s bristling standard, which landed Saturday like an angrier follow-up to the Buffalo Springfield’s “For What It’s Worth.”

Mayer took his own crazed solo, followed by Stills, and then Young closed with a final flurry of notes, flailing and cataclysmic, as always. At the end, Young looked pleased, another trunk of memories secure.