If you drive west across Iowa’s farm plain toward its Missouri River border, suddenly you will encounter the Loess Hills, windblown silt rising up from the ﬂat prairie to dominate the horizon. The Loess Hills are a relief in the landscape, or an irregularity of the Earth’s surface. Vertical relief provides a change in one’s view of the setting, and it is often the focal point of a visitor’s ﬁrst impression of a place. Speciﬁcally, relief means the difference between high and low points in the landscape—the variations in elevation and horizontal spacing that exist among landforms. Relief can be considered at a variety of spatial scales. For example, one might speak of the local relief—the difference between the hills versus the valley bottoms in an area. Or one might speak of the relief that exists across a continent—the difference between Death Valley and Denali National Park and Preserve. Still further, one might speak of relief across the globe, including the ocean depths—the difference between the Mariana Trench (the lowest point below sea level) and Mount Everest (the highest point above sea level): 65,236 feet.