After Lewis and Clark opened the frontier, thousands of people—mostly men— poured into the far West. Many made their living from one simple item—the beaver hat. From the early seventeenth century to the middle of the nineteenth century, no proper European gentleman would appear in public without one. Hatters could scarcely keep up with demand. In 1760 alone, the Hudson Bay Company exported enough beaver pelts to England to make 576,000 hats.

In addition to beaver, the North American "skin game" provided pelts, called "brown gold," from marten, fox, and otter. They were turned into collars, sleeves, hems, gloves, and boots for men and women alike.

For two hundred years, the fur trade was the main trade of the North American wilderness. Animal pelts were the only things of value thought to exist there. As early as...