If alt-country has a creation myth, it’s the 1973 funeral of Gram Parsons — his OD’d corpse stolen by road manager Phil Kaufman and cremated in the desert at Joshua Tree, California, a fitting end for the only rock star whose name was a synonym for a quantity of drugs.

For Parsons, born Cecil Ingram Connor, it had been a strange trip: A rich kid, he went to Harvard, frittered his trust fund and influenced the Rolling Stones. He also experimented with a new blend of country, rock and soul, which he dubbed “cosmic American music,” a brand that works as well for Wilco and Lambchop in 2003 as it did for the Byrds in 1968.

Drafted early that year by Roger McGuinn and Chris Hillman to replace the skedaddled David Crosby, Parsons was a Byrd for less than five months, and due to contractual wrangles, only two compositions and two lead vocals made the original release of the gently rocking, pedal steel–laced Sweetheart of the Rodeo. This two-CD set sketches the band’s future, with a wealth of Parsons’s rehearsal takes (including a transfixing “One Hundred Years From Now”) and a handful of tunes by Parsons’s pre-Byrds group, the International Submarine Band.

The context is helpful, but the Classic Coke version of Sweetheart remains unbeatable. The teetotal ballad “The Christian Life” is made unspeakably poignant by the incorrigible druggies singing it, and Parsons’s almost-solo “Hickory Wind” is sublime, fog-eyed nostalgia. Perhaps best of all, McGuinn and Hillman’s brilliant harmonies on the “original” “One Hundred Years From Now” prove how much Parsons’s tunes benefited from a thorough group overhaul.

But the partnership didn’t last. Parsons left in July 1968, adding new chapters to country-rock as a solo artist and with the Flying Burrito Brothers, while McGuinn’s Byrds stuttered to a protracted demise. Sweetheart endured, placing generations of freaks and punks — many looking to reclaim country as an alternative genre — under its spell. Thirty-five years later, its legend is deserved.