Sandy Gebhards was born allergic to her mother's milk, bucking convention, she says, "right from the beginning," out of the womb with her fists up. Her parents' first child, a boy, had died as a baby; Gebhards supposes she became the son they had lost. The family lived in Jerome, Idaho, then Boise, and she and her father spent weekends fishing and skiing in the Sawtooth Mountains. After high school, she worked in Stanley, in lodges and mines, fixed fences, drove plows. Though her parents encouraged her education, she drifted in and out of Boise State, where she studied ceramics. She preferred the work that others said she couldn't do.

By the age of 52, Gebhards had married and divorced and raised two girls in McCall, an Idaho resort town. She ran a business, laying fine tile and mosaics in second homes. In the recession, the jobs stopped coming, and several clients never paid. "I could declare bankruptcy and walk away, but I'm afraid to wreck my credit and lose everything I've built," she later said. She was in debt, with one daughter in college and another in high school. "They've watched me struggle to make a living, to take care of them all their lives. When I asked them, 'Do you want me to stay here?' they said, 'No. You need to go.' "

In March 2012, Gebhards left for the Bakken oilfields in North Dakota, where an acquaintance, Gary, drove an oil truck and found her a job on his crew. In the cluster of trailers in a farmer's field where she first lived, she didn't talk to anyone. The only man's eyes she met were Gary's. They shared a truck and a camper -- he drove a shift, then she did -- and saw each other in passing. On days when she had eight hours' rest, she bought food and washed clothes; a single load cost $30. Mostly, she slept. "I was so relieved to work for someone else," she said. "For the first time in years, I slept like a baby."

When Gebhards was 19, she worked as a cook at a remote hunting lodge in the Frank Church Wilderness. One evening, two drunken clients cornered her in the kitchen. She pulled a butcher knife from the counter, cleaved the air between them, ran out the backdoor, and rode a horse to a ranger station, where she caught a flight out in the morning. Her coworkers had watched it happen. When she later asked them why they hadn't stepped in, they said the men were high-paying clients. After that, she carried a gun. "I don't look at anybody. I don't smile at anybody. I just blend in as much as possible. I've done this all my life."

The oilfields are "no place for a woman," Gebhards was warned. According to the Bureau of Labor Statistics, men hold 85 percent of the jobs in the mining, oil and gas industries. Outside of administrative and management positions, women hold less than 2 percent. In the Bakken, women say they no longer feel safe; police departments report rising rates of sexual assault. But western North Dakota is one of few places in America where, mid-recession, someone with limited training is guaranteed a living wage. Last year, semi-truck drivers there earned, on average, $50,000 a year; in the state's oil and gas industry, the mean salary was $90,000. Gebhards, accustomed to being the only woman on a job, was determined not to miss out.

Some men acted surprised to see her working; others hardly seemed to notice. She didn't "go asking for trouble," she said -- didn't drink at bars, go where the prostitutes lingered, shop at Wal-Mart at 2:00 a.m. She found it thrilling enough to drive an 83-foot-long truck across the prairie, dragging that oil bomb behind her, around flares and pits and over scoria roads. She liked the physicality of it all, climbing the tanks, lowering in the gauge to read the temperature. It took half an hour to pump 80 barrels if the oil wasn't too cold. Then there were long, quiet stretches, nothing to look at but pump jacks and empty homesteads. What desolate country it was, she often thought -- what a burden it must have been to warm those brittle houses.

In her time on the Bakken, she saw only one other woman hauling oil. Gebhards' boss sometimes asked if she had "slept (her) way" into the job. "It bothers me, but what can I do?" she said. "There's a fine line between defending yourself and keeping your mouth shut so you don't get fired." One night, she was returning to Williston with a load when her brakes locked and wheels caught fire. She searched the cab in vain for an extinguisher and stifled the flames with handfuls of gravel. When her boss blamed her for the incident, she quit, but he begged her to come back. The company was short of drivers, and Gebhards sometimes worked several days without rest. She drank coffee and Red Bull and smacked her thigh to stay awake. If she was lucky, she would be sent to the rail yard, where she could nap in intervals until it was time to unload. Her paycheck, averaging $10,000 a month, made it all bearable, and so she let Gary negotiate her return. "Just tell Sandy where she needs to pick up and drop off," Gebhards recalls him telling their boss. "Nothing more."

If she stuck it out for five to 10 years, she could pay off her debts and have enough to retire. But even in North Dakota, earning a steady income was more difficult than she anticipated. In June 2012, while stopped at an intersection near Williston, she was rear-ended at 70 mph. She remembers only that she couldn't move, and that when a man came to her window to ask if she was all right, she said she didn't know.