Unwittingly, however, they were approaching Powell’s 100th meridian, moving into the land that would inspire the tornado-scarred, wind-whipped plains of The Wizard of Oz. In Minnesota, while subject to locust swarms, the Ingallses had nonetheless inhabited a place where twenty-three to thirty-nine inches of precipitation fell reliably every year. In Dakota Territory, they entered a different world, where thirsty crops could expect only fifteen to twenty-three inches annually—if they were lucky.
