LOS ANGELES — John David “JD” Souther, a prolific songwriter and musician who helped shape the country-rock sound that took root in Southern California in the 1970s with his collaborations with the Eagles and Linda Ronstadt, has died at the age of 78.

Souther, who collaborated on some of the Eagles’ biggest hits, such as “Best of My Love,” “James Dean,” “New Kid in Town,” and “Heartache Tonight,” died Tuesday at his home in New Mexico, according to an announcement on his website.

He also worked with James Taylor, Bob Seger, Bonnie Raitt and many more, and also found success as a solo artist. He was about to start a tour with Karla Bonoff on Sept. 24 in Phoenix, now canceled.

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A Principal Architect of Southern California Sound

When he was inducted into the Songwriters Hall of Fame in 2013, Souther was described as “a principal architect of the Southern California sound and a major influence on a generation of songwriters.” He was also at the heart of the social scene, his girlfriends including Ronstadt, Joni Mitchell and Stevie Nicks, who in a 1982 interview with High Times magazine remembered him as “very, very, very male chauvinistic and very sweet and cute and wonderful but very Texas.”

Souther was born in Detroit and grew up in Amarillo, Texas. He moved to Los Angeles in the late 1960s, where he met fellow Michigan native Glenn Frey, a founding member and guitarist of the Eagles. The two began a longtime partnership, starting with a band called Longbranch Pennywhistle. Frey would credit Souther with introducing him to country music.

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Close Ties with the Eagles

“Our first year together will always seem like yesterday to me,” Souther said in a statement after Frey died in 2016. “His amazing capacity for the big joke and that brilliant groove that lived inside him are with me, even now, in this loss and sorrow. … The music and the love are indestructible.”

Souther was so close to the Eagles, he even appeared on the back cover of their 1973 album, “Desperado,” with Souther and others reenacting the capture of the legendary Dalton Gang. He described his start with Frey at The Troubadaour, the popular West Hollywood music club, as “the best study in songwriting I can imagine.”

“So many great songwriters came through — Laura Nyro, Kris Kristofferson, Randy Newman, Elton John, James Taylor, Tim Hardin, Carole King, Rick Nelson, Joni Mitchell, Neil Young, Waylon Jennings, Tim Buckley, Gordon Lightfoot, Taj Mahal and more,” he said in a statement on his website. “It seems impossible now to imagine that much music in a year and a half or so, but that was my life and the Troubadour was our university.

“It’s also where I met Linda Ronstadt and where Don Henley and Glenn Frey met to form this little country rock band called Eagles that would go on to make musical history,” Souther wrote.

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Solo Career and Collaborations

On his own, Souther recorded his self-titled debut in 1972 before forming The Souther-Hillman-Furay Band with former Byrds member Chris Hillman and Poco’s Richie Furay. A second solo effort in 1976, Black Rose, included a duet with Ronstadt, his one-time girlfriend, “If You Have Crying Eyes.” Other duets he had recorded with her include “Prisoner in Disguise,” “Sometimes You Can’t Win” and “Hearts Against the Wind,” the latter featured in the 1980 film “Urban Cowboy.”

His biggest hit as a solo artist was “You’re Only Lonely,” from the 1979 album of the same name.

Other songs he wrote include “Run Like a Thief,” for Bonnie Raitt, and “Faithless Love” and “White Rhythm and Blues” for Ronstadt. He collaborated and sang with James Taylor on “Her Town Too.”

Among other artists he worked with as a singer were Don Henley, Christopher Cross, Dan Fogelberg and Roy Orbison.

He appeared as an actor on television in “thirtysomething,” “Nashville” and “Purgatory” and in the films “Postcards from the Edge,” “My Girl 2,” and “Deadline.”