Lily Casey and her two younger siblings, Buster and Helen, are bringing the cows in from pasture when a flash flood hits. Lily helps her siblings take shelter in a tree. Upon returning home the next day Mom asserts, to Lily’s annoyance, that her prayers saved them.
The family raises cattle on unforgiving terrain in western Texas. Dad trains carriage horses, which he loves despite having been hit in the head by one as a child and developing a speech impediment as a result. They live in a dirt dugout until it is destroyed by a flash flood when Lily is eight, at which point they build a wooden house from scavenged lumber. Dad writes prolifically, often railing against industrialization. Lily is in charge of breaking horses and is thrown often, though Dad insists falling is an important part of life. He also teaches Lily that everyone has a “Purpose in Life.”
When Lily is eleven, a tornado destroys their house and the family moves back to their family ranch (which Dad dubs the KC Ranch) in New Mexico. At thirteen, Lily enrolls in a Catholic girls’ school. She loves learning and Mother Albertina, the school’s Mother Superior, encourages her to think about teaching. Lily is forced to drop out, however, when Dad spends her tuition money on four Great Danes. Back at the ranch, Old Man Pucket shoots the dogs, mistaking them for wolves. He repays the Caseys with horses, one of which Lily claims and names Patches.
With World War I going on, there is a shortage of teachers. As such, despite being only fifteen Lily is able to find a teaching position in Red Lake, Arizona. She makes the 500-mile journey by herself on horseback. Lily loves being a teacher, but is forced to return home when the war ends. During the ride back to the ranch she sees a red airplane in the sky, causing her to realize that her father’s horse carriage business is doomed.
Intent upon seeing more of the world, Lily boards a train to Chicago. She finds work as a maid and attends women’s suffrage rallies with her roommate, Minnie Hagan. Minnie is suddenly killed when her hair gets caught in factory machinery. Reflecting on how unpredictable life is, Lily cuts her own hair to just below her ears. Shortly afterwards she meets Ted Conover, a smooth-talking salesman. After six weeks of dating, the two marry. Soon, however, Lily learns that learns that Ted has another wife. She annuls the marriage and leaves Chicago. Red Lake offers to give her back her job.
While competing in a horse race Lily meets Jim Smith, the owner of the new auto garage in town who teaches her to drive. Helen, who has moved to Los Angeles to become an actress, writes to say that she is pregnant, and the father has abandoned her. Lily agrees to take her in, but once Helen’s condition becomes known the town shuns both sisters. Mr. MacIntosh, the superintendent, says Helen must leave. Distraught, Helen hangs herself.
In her grief Lily realizes she wants to have a baby and approaches Jim Smith about marriage. He readily agrees. After marrying, the two leave Red Lake for the town of Ash Fork, where they run an auto garage. Lily gives birth to a daughter, Rosemary, and a year and a half later has a son, Little Jim. With the country in the middle of the Great Depression, Lily resorts to selling bootleg alcohol to make ends meet. They are forced to close the garage, but Jim eventually secures a job managing a 100,000-acre ranch.
Realizing the land has no source of water, Lily suggests building a dam, and Jim convinces investors to let them rent a bulldozer. The following year Jim convinces the English investors to buy the neighboring Hackberry ranch, which has a windmill with well water. Lily loves Hackberry so much that she decides she wants to buy it and comes up with various money-making schemes.
Lily takes her first flying lesson shortly before her thirty-ninth birthday and feels as though she is seeing the world for the first time. Still needing more income, she then gets a teaching job in a town of Mormon polygamists. She attempts to teach her female students that there is more to life than churning out babies, which angers the local patriarch and gets her fired. Lily finds another job in Peach Springs, where she agrees to be the teacher, janitor, cook, and bus driver all at once. She buys a used hearse to employ as a school bus during the week and a taxi on weekends, putting the extra money towards flying lessons. But when Lily spanks the trouble-making son of a local deputy after he sticks his hand up a girl’s skirt, her contract is not renewed. Lily insists she does what is necessary when the rules are wrong, but she is tired of being fired.
Sensing that their own children need more “civilizing,” Lily and Jim send both to boarding schools while Lily finishes her degree in Phoenix. Rosemary is kicked out of the academy for being too disruptive. By then, however, Lily has earned her college degree and finds another teaching job in a town called Big Sandy. Rosemary blossoms into a pretty teenager and develops a crush on a ranch hand. After she is caught swimming with him, a furious and distraught Lily beats her to teach her a lesson. In response, Rosemary says she will never beat her own children. Lily reflects that her daughter stops listening to her from that day forward.
When the ranch gets sold out from under them, the family moves to Phoenix, where Lily teaches at a high school and Jim gets a desk job. Despite the comforts of city life, the family grows restless being so disconnected from nature. Lily also resents the seemingly endless bureaucracy of her new school. She suspects Jim is cheating on her, but after confronting him the two realize city life is driving them crazy and they move to the town of Horse Mesa.
Both Rosemary and Little Jim attend Arizona State, but the latter drops out upon getting married and then becomes a police officer. In her third year of college, Rosemary falls in love with the charming but unstable Rex Walls. Lily, who think Rosemary needs someone to anchor her, does not approve of the match. She laments that Rosemary is the one child she could never teach. She warms up to Rex, who is in the air force, when he takes her flying. Rosemary and Rex marry, and as they drive away from the wedding they look to Lily and Jim like “a couple of half-broke horses.”
In the epilogue, Lily notes that Rex continues to bounce between odd jobs and hatch hair-brained schemes, and he and Lily frequently argue viciously. Rosemary and Rex live a nomadic existence around the desert. Their third baby is a daughter they name Jeannette, with whom Lily feels an immediate connection. Lily senses that her grandchildren have a wild ride in for them, but says they come from hardy stock and that there is nothing that can stop Lily from teaching them a few things.