In October 1887, in Prosperity Creek, Montana Territory, 17-year-old Ara Kowalski and her widowed mother Anna were evicted by the town council. The council gave them a worthless 3-acre plot called “the Barrow” — a steep, rocky, north-facing slope with almost no usable timber, poor water, and a shallow cave known locally as the “bear’s mouth.”

Thomas Baird was Prosperity Creek’s master builder. He had put up nearly every proper cabin in the valley, including the town hall itself. He was a man of plumb lines,…

In the summer of 1886, 23-year-old Ingred Torsdaughter arrived in Montana Territory with nothing but $7 sewn into her dress and a job offer to herd sheep for the Grande family near White Sulphur Springs. The fourth of nine children from a poor tenant farm in Norway, she had crossed the ocean and traveled by train, then wagon, across 70 miles of empty prairie to reach the remote line camp on the Musselshell River.

Croft almost smiled. Tar paper, he said, was $2 a roll, and she would need at least 4 rolls. Canvas was cheaper, 80 cents a yard. Most people who could…

At just 15 years old, Ingred Larsen was told she had to leave her aunt’s home before the first frost hit. It was late August 1883 in Elhorn, Nebraska Territory. Her aunt Elsa had recently married a farmer named Otto Schmidt, and Otto made it crystal clear: he wasn’t willing to feed or shelter his new wife’s orphaned niece when his own six children already took up every available resource.

That memory gave structure to her plan. She would build a dugout, but not a simple hole. She would build one with a heating innovation based on the same principle…