Otis Granville Clark is a wonder. At 102, the former butler of Joan Crawford - who served Clark Gable and Charlie Chaplin - still drives, lives on his own and twice a week attends church in his home city of Tulsa, Oklahoma. He has been a church-goer for decades, ever since he heard the call and, surprising Crawford and himself, became an evangelist preacher. Today his blue eyes have gone milky but they still sparkle, his wiry frame remains agile, and his most painful memories are still fresh - even after 83 years.

Coiled on the edge of an understuffed sofa, Clark leans back and screws his eyes tight to summon up "that day". It remains the most vivid of his life. "That was the day I saw blood," he says. He was a young black man of 18, scarcely aware of the world beyond his neighbourhood on that warm spring morning in 1921 when "the shooting and all" began.

Most days, he would have been working with the bootleggers making corn whiskey down by the Arkansas River. But that morning he had gone to a relative's funeral home, a block from the heart of the violence. He had tried to help a friend save the business's prized new acquisition, an ambulance, when "these white snipers in a mill tower started shooting from across the way. They shot wherever they could see black folks, swatting them like flies." His friend had the keys in his hand when a bullet pierced it. The blood stained Clark's shirt. "And that was before the worst of it started."

Historians call the firestorm that convulsed Tulsa from the evening of May 31 into the afternoon of June 1 the single worst event in the history of American race relations. To most Tulsans it is simply "the riot". But the carnage had nothing in common with the mass protests of Chicago, Detroit and Newark in the 1960s or the urban violence that laid siege to Los Angeles in 1992 after the white police officers who assaulted Rodney King were acquitted. The 1921 Tulsa race riot owes its name to an older American tradition, to the days when white mobs, with the consent of local authorities, dared to rid themselves of their black neighbours. The endeavour was an opportunity "to run the Negro out of Tulsa".

Clark lives in a quiet bungalow. There are three square rooms filled with worn furniture and decorated with little but bibles and church pamphlets. It sits squarely in the blighted heart of North Tulsa - the city's "predominately black neighbourhood", to its older residents; "the "hood", to their grandchildren. In 1921, a leafy neighbourhood sprawled here. Back then it was called Greenwood, and it was a black neighbourhood as affluent as any in America. Its small but thriving business district was dubbed "black Wall Street". Greenwood, as Clark and other survivors remember it, was a city within a city. "We had it all," he says, "Shops, schools, movie theatres, doctors, lawyers, newspapers - you name it."

Sixteen years earlier a vast petroleum field had been discovered nearby, and by 1921 Tulsa had become known as "the oil capital of the world". The town was awash in oil dollars, and the ascendant class of oilmen and their families needed more than domestics - they needed a service sector. Greenwood bloomed. Less than 60 years after the Emancipation Proclamation, as many as 10,000 blacks enjoyed the quiet and prosperity on the western edge of the Ozark Mountains. But Greenwood posed a challenge. "The old order would not stand much longer," wrote legal scholar Alfred Brophy in Reconstructing the Dreamland, the most recent of more than half a dozen books on the riot. "It was a culture that would not easily abide unequal treatment."

The riot began, as the battles in America's race wars often seem to, with an allegation of sexual assault. On the warm afternoon of Memorial Day, May 30, 1921, in the Drexel Building that still stands downtown, a 19-year-old black shoeshine boy named Dick Rowland had gone to the "coloured" men's toilets on the top floor. Sarah Page, a 17-year-old white girl - an orphan, Tulsans were soon told, working her way through college - ran the elevator. What transpired between the two remains a mystery, but whether Rowland tripped, or grabbed Page's hand, or never even touched her, the girl screamed. It was enough. By the following afternoon, a front- page headline in the Tulsa Tribune, trusted daily of the town's white citizens, exhorted: "Nab Negro for Attacking Girl in Elevator". Rowland, the Tribune cried, had attacked Page. The spectre of rape raised, the lynching calls ensued....