When salt lakes dry up, whether permanently or temporarily, their beds become salt or alkali ﬂats, glistening stretches of level, pale ground encrusted with saline minerals such as potassium, magnesium lithium, and sodium chloride. The evaporation of winter rains deposits salty materials—originally in solution—onto the ﬂoor of the lake basin, already smooth and ﬂat because of its silt and clay base. Such is the case with the vast Bonneville Salt Flats west of Salt Lake City, Utah. Its more than thirty thousand acres are so buffed that for decades it has been the site for attempts on the world land speed record. Rogers Dry Lake on Edwards Air Force Base in California is ﬁrm and ﬂat enough that it is used as a landing area for spacecraft. In the Southeast, the term salt ﬂat is used quite differently. There it denotes low-lying, grassy coastal land, sometimes ﬂooded with salt water but not as continuously wet as a salt marsh.