Sawers (2005) shows how southern farmers made the mule their preferred draft animal in the South during the 1860s–1920s, primarily because it fit better with the region's geography. Mules better withstood the heat of summer, and their smaller size and hooves were well suited for such crops as cotton, tobacco, and sugar. The character of soils and climate in the lower South hindered the creation of pastures, so the mule breeding industry was concentrated in the border states of Missouri, Kentucky, and Tennessee. Transportation costs combined with topography to influence the prices of mules and horses, which in turn affected patterns of mule use. The economic and production advantages associated with mules made their use a progressive step for Southern agriculture that endured until the mechanization brought by tractors. Beginning around the mid-20th century, Texas began to transform from a rural and agricultural state to one that was urban and industrialized.