sentence: Salt flats are very unusual.
sentences_before: Some of these features include sand dunes, salt flats, colorful rocks, and tall mountains. Large parts of Death Valley are below sea level. One feature, named Badwater Basin, is the lowest place in North America. It is  below sea level. The salt flats are another famous feature in Death Valley.
sentences_after: They are large, flattened areas where the surface of the ground is covered by salt instead of dirt. The salt that makes up a salt flat can be many inches or centimeters deep. The salt flats were created because thousands of years ago, Death Valley was underwater. Lake Manly used to be very large, but changes in the weather caused the rivers that brought water into the lake to dry up. After a long time, the water in Lake Manly began to dry up too.
concept_name: salt flat
headings: Death Valley Geography
categories: Deserts Geography of California Valleys in the United States Wilderness Areas of the United States