YOU ALWAYS know when you're listening to a Johnny Cash song. His distinctive dark baritone, which conveyed everything from lust to spiritual terror with grave authority, made sure you never mistook him for anyone else. And no one else ever copied adequately Cash's boom-chicka-boom, the bluesiest of country beats, mimicking the rhythms of the trains that plowed through so many of Cash's songs, giving the tunes a sense of profound, endless openness. Developed early in his career with guitarist Luther Perkins and bassist Marshall Grant, Cash worked on variations of that beat until his final album, released last year. Cash was inducted into three Halls of Fame: Country, Rock 'n' Roll, and Songwriters. It's easy to think those communities don't overlap, but Cash's whole career was about uniting things most people thought were far apart.

Cash transcended limits cultural and political, not just music. Cash wrote a novel based on the Gospel of Paul and shared racy jokes with death-row prisoners; Cash had both Bob Dylan's and Richard Nixon's home phone numbers. His ability to get on the same level with different groups seemed infinite.

In recent years, his greatest popularity was among people generations his junior: He recorded with U2 and other rockers, and his final albums were full of songs associated with Depeche Mode, Nine Inch Nails, and Soundgarden. Cash was the greatest American-music uniter aside from Elvis Presley.

Cash served as a lovely symbol in an era of separation and differentiation, but he saw himself primarily as a performer. I'd argue that Cash's greatest music came at the beginning and near the end of a career that spanned six decades. On Friday, the day he died, I surrounded myself with his '50s recordings for Sun Records and was struck by how current they feel. Today's alt-country and alt-rock kids are still going for the bare-boned sound of songs like "Folsom Prison Blues," "Hey Porter," "I Walk the Line," "Get Rhythm," and "Train of Love," which anticipated future marriages of hard country and hard rock.

These numbers call on the unswayable rhythms of the rails to carry tales of fidelity, regret, adventure, and most often all at the same time, with such lines as "Everyone's baby but mine's comin' home" and "I shot a man in Reno just to watch him die." Cash bought all the myths of honky tonk, but he knew that Elvis had changed the world by fastening country to the blues, and he tried to find himself a home in it.

In "Come In Stranger," the erotic tale of a country singer (like, say, Cash) being welcomed home after a long haul on the road, all the contradictions come together and add up to a complex life worth hearing about. Cash's Sun years represented only the beginning of Cash's great story, but they do suggest nearly all of the high points ahead.

Until the end, that is. Cash's last four albums, his most raw recordings since his Sun days, showed how much he'd learned in the intervening years yet how close he still felt to his original method. Age and gravity held down his voice, and when he'd start a song with a line like "Everyone I know goes away" (from "Hurt," off his final record) he sounded ready to knock on heaven's door. Like Warren Zevon, another outstanding performer and songwriter who died last week, Cash wrote an obituary more eloquent than any of us left behind could.

It's impossible to overstate how alive Cash's music was, even in his later years. The last time I saw him perform in person was in March 1994, in Austin, Texas, as part of the South By Southwest music-industry conference. Earlier that day he'd delivered a brief, funny, motivational speech to the assembled young flannel-shirted Nirvana wannabes; now he was the first act on a long bill that would end five hours later with the Next Big Thing, a kid named Beck.

First alone with his guitar and then with a lanky three-piece backing, Cash approached his material furiously, diving into takes of murder, train whistles, post-traumatic stress disorder, raising horses, prison rape, and spiritual desolation with a ferocity the punks later on the bill could only hope to attain in their dreams.

Cash was a uniter, willing to venture to the middle of the road to please those who might be distressed by his more penetrating visions, but it's what he achieved when he rode the side roads that won't ever go away.

Jimmy Guterman's books include "Rockin' My Life Away." He produced "The Sun Records Box."

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