Jane Smiley, author of 12 novels, several biographies and five young-adult novels, puts it down to the role of landscape, which she considers the most important aspect of the novel. It explains why the midwest takes pride of place in her fiction. In fact, it would be fair to say Smiley's entire oeuvre derives from the midwest experience.

She's not alone. The midwest, after all, has been the birthplace and inspiration of some of  the United States' most venerated novelists, including Mark Twain (Missouri) and Kurt Vonnegut (Indiana), as well as the contemporary authors Toni Morrison (Ohio), Jeffrey Eugenides (Michigan) and Garrison Keillor (Minnesota). Jonathan Franzen, who has been called one of "America's best living novelists" and whose most famous novels, The Corrections and Freedom, are set in the midwest, was born in Illinois and grew up in St Louis, Missouri.

Smiley, whose novel A Thousand Acres, which retells King Lear on a farm in Iowa and won the 1992 Pulitzer Prize for fiction, was born and raised in St Louis, the  geographical heart of the midwest. She lived for 24 years on a property in Iowa, where she bred horses, a favourite topic of her fiction. But defining the midwest isn't easy. "The definition always shifts," she says.

Smiley, 65, has three grown-up children and now lives on a farm in Carmel Valley, California, with her fourth husband, Jack Canning, four horses and a couple of noisy dogs, but she has returned to Iowa for the setting of her new novel, Some Luck, the first in a trilogy with the working title "The Last One Hundred Years".

Some Luck is about a hard-working farming family, Walter and Rosanna Langdon and their five children, who experience the hardships and rewards of 20th-century rural life. The story begins in 1920, when the Langdons' first child, Frank, is born, and ends in 1953, with each chapter representing a year. The trilogy will end in 2019, covering a century and charting the 45 lives in the Langdon family tree.

Frank, whose good looks and charm endear him to people in the outside world, grows up with itchy feet and heads off to the big smoke, while his younger brother, Joe, and other Langdon children remain on the farm, a crucible for nurturing and renewal. Their individual stories build a portrait of midwest farm life.

At times, little seems to happen in the story, reflecting the occasional torpidity of rural existence; at other times, events take off: Rosanna's sister, Eloise, relocates to Chicago and engages in left-wing politics; conscripted Frank ends up in Europe and North Africa fighting in World War II.

As Smiley says, if you want characters to move in a story, there is no better place to have them start out than on a farm.

The cultural mix of the midwest intrigued Smiley when she was growing up. St Louis was full of French, Italians and Germans, so it considered itself a melting pot. The land between Ohio and west Nebraska – which takes in the midwest states of Iowa, Indiana, Illinois and Missouri – is the most fertile, which is why European immigrants loved it.

"For a long time, that part of the country was oddly diverse," she says. "The area where, say, Wisconsin, Minnesota, Illinois and Iowa meet was where, in the 1840s, people would find a nice place to live, exactly as they had lived back in Europe."

In Some Luck, Walter's family "was a bastard mix ... with some of those long-headed ones from the Borders, with red hair, and then some of those dark-haired Irish from Wexford that were supposed to trace back to sailors from the Spanish Armada, and some tall balding ones who always needed glasses from around Glasgow". Rosanna's family, "the Ausbergers and the Vogels", are of German descent, and Catholic.

Smiley first came up with the concept of the trilogy during a lunch in Los Angeles five years ago with the Australian author David Francis. "I told him this idea about the trilogy and he said, 'Don't you dare tell anybody this or someone will steal it'. And so I have to say I owe it all to David."

Smiley grew up in a family of storytellers. Her father, a tall man (Smiley herself is 188 centimetres tall) who served in the war and was treated in a veterans' hospital with a mental disorder when Smiley was a baby, was absent for most of her life and although she had no siblings, she had many cousins.

"My mother had four brothers and sisters. They were all quite talkative about their childhoods. And so my cousins would get the pictures out and encourage my grandparents, my mother and aunts and uncles, to tell the stories from the old days."

The father of Smiley's grandmother was a newspaper editor and the mother was a Norwegian immigrant. They met in Minnesota and moved to Idaho, where he took over a newspaper.

"My grandmother and her brother were born in Idaho, and my grandfather was from Missouri. His older brother had got into some trouble from a bar fight and so their mother sent the two boys out to Idaho, enabled them to finance a ranch, and that's where he met my grandmother, an itinerant schoolteacher."

The ranch failed and the pair moved to Texas, where Smiley's grandfather entered the oil business.

Smiley took up writing when she was 17. During her first high school spring break, she spent two weeks with friends in England, where she "even bought a mini skirt". When she returned home, she wrote a paper about her trip. "I got an A and I thought this is really fun, I like this." Later she attended the University of Iowa, completing a PhD in creative writing after doing a master's degree at the college's celebrated Writers' Workshop.

Her first novel, Barn Blind, about a horse-riding family, was published in 1980. Another novel, Horse Heaven, about racehorses, which Smiley herself once invested in – unwisely, she admits – was shortlisted for the 2002 Orange Prize, and Franzen has said her 1988 novel The Greenlanders, a family saga about 14th-century Nordic immigrants, is "among the best contemporary works of American fiction".

Smiley has also written a biography of Charles Dickens, one of the 19th-century novelists she counts among her literary mentors, along with Jane Austen and Anthony Trollope. Dickens' novel  Our Mutual Friend is one of her favourite books, because of the "strangeness of the Dickens landscape and his characters".

"I came to Trollope late, but what I liked about him was the lack of strangeness, the familiarity," she says. "I always say that Dickens writes about the edge of sanity and Trollope writes about the middle of sanity, being sane. The characters are individual, but they are normal and recognisable, so in some ways the choices they have to make are more painful, because they are the choices that we have to make. We never have to make the same choices as the Dickens character."

Smiley's devotion to 19th-century novelists perhaps explains why her own fiction is heavily detailed, whether it is about the landscape, the weather or, as in the opening of Some Luck, how Walter contemplates an old elm tree housing a pair of owls.

Detail adds accuracy to her stories, she says, and helps readers understand the world inhabited by her characters. She once criticised The Great Gatsby, considered by many to be "the great American novel", for being 100 pages too short, because it lacked "detailed development of characters and their relationships".

"What I always say about the novel, as opposed to a play or poetry, is that the novel is really about 'how' – how something happens. For example, if you look at Don Quixote, it is not nearly as interesting to know he went out and considered himself a knight, but how he did it, what the horse looked like, what weapons looked like, what his enemies looked like, how he moved across the landscape."

In the midwest, farms have grown larger over the years to accommodate new methods of food production. People have moved away and the towns have shrunk as a result, but Smiley disagrees that her new novel celebrates, as one critic noted, "a world long gone".

"Yes, that world has changed. The self-sustaining small family farm – that's gone," she says. "But the people who live there wouldn't necessarily say that world has long gone. Not at all. The midwest also has a lot of continuity."

Some Luck, by Jane Smiley, is published by Mantle, $29.99. Early Warning, the second in the trilogy, will be out in April.

And another thing

Smiley has dedicated Some Luck to her current husband and three former husbands, with whom she remains good friends.