IN 1970, when she was 36, Joan Didion, accompanied by her husband, the writer John Gregory Dunne, visited the American South. She had not been there for nearly three decades; during the war her father, who was in the Army Air Corps, had been stationed at Durham, North Carolina, where Didion and her mother and brother regularly visited him. It did not invoke the happiest of memories.

Why she decided to return remains to her a mystery. At the time she was living in Hollywood and already the author of Slouching Towards Bethlehem, which perhaps captures the anarchic, idealistic, hedonistic spirit of the Sixties better than any other book. By her own account, there was little to draw her to the South, no celebrity murders, no trials, “not even any celebrated acts of God”.

Nor did she manage to write a piece about her time there. Instead, she kept a notebook, jotting down things she saw, or overheard, or struck her as remarkable, or remarkable in their ordinariness. It was hot, hell hot, and humid, hot tub humid. Dead dogs lie by the road side. Her husband drives over three snakes in one hour. A woman dies at the wheel of her car. Death and decay were pervasive, “not violent death,” as she observed of New Orleans, “but death by decay, overripeness, rotting, death by drowning, suffocation, fever of unknown etiology”.

The South, as anyone who has ever been there will attest, is a nation apart and adrift from the rest of the US. It was even more so in the 1970s. Insouciantly racist, doggedly class-ridden, insistently polite, religiously fanatical, pathologically parochial, it did not open its arms to strangers, especially women like Didion who wore their hair straight and cooled off in a bikini in motel pools. What form, she wonders, would her anger have taken had she lived there full-time? “Would I have taken up causes, or would I have simply knifed somebody?”

Most likely she would have gone out of her mind with boredom or drunk herself to oblivion or found a means of escape. What strikes one is the apathy, the lack of curiosity, the complacency. Segregation is accepted, black people talked of as if they are another species. “I cannot think of any place where the black is denied entrance,” the white owner of a black radio station tells Didion, “with the possible exception of private clubs.” Meanwhile, bus drivers won’t start up until she moves from the black back section of the vehicle to the front.

The second, and much shorter – and slighter – part of South and West consists of notes Didion made in 1976 in preparation for a piece she hoped to write for Rolling Stone about the Patty Hearst trial. Nothing immediately came of it but eventually, in 2003, it proved the spur for her memoir, Where I Was From. “I am at home in the West,” she writes by way of valediction. “I am easy here in a way that I am not easy in other places.” In the South this most wonderful of reporters was a far cry from easy.