During the 1830s and well into the 1840s, before the McCormick reaper and the Deere plow had worked their act of transformation, the western plains were known as the Great Desert, and they remained largely unsettled. Instead, settlers first set their sights on the Far West. By the early 1830s, Americans were beginning to settle in California, many of them “mountain men”—fur trappers—who turned from that profession to ranching and mercantile pursuits.
These pioneers made their way into the territory by way of the southwestern deserts until 1, 833, when Joe Walker, a mountain man from Tennessee, marched due west from Missouri. Walker took the so-called South Pass through the Great Divide, went east to west across the Great Basin, climbed the Sierra Nevada Mountains, and entered California. This path became the California fork of what would be called the Overland Trail. Walker had opened California to the rest of the nation. By 1840, 117 mountain men were settled in Mexican California, bringing the American population to about 400.