In physical geography, a cliff is a significant vertical rock exposure. A scarp is a type of cliff, formed by contraction. Cliffs are common on coasts, in mountainous areas, escarpments, and along streams. Generally speaking, cliffs are formed by rock that is resistant to erosion and weathering. Sedimentary rocks most likely to form cliffs are sandstone, limestone, chalk, and dolomite. Igneous rocks, such as Granite and basalt, also often form cliffs.
Most cliffs have some form of talus slope at their base. In arid areas or under high cliffs, these are generally exposed jumbles of fallen rock. In areas of higher moisture, a soil slope often obscures the talus.
Many cliffs also feature waterfalls or rock shelters. Sometimes a cliff peters out at the end of a ridge, with tea tables or other types of rock columns remaining.
Some of the highest cliffs in the United States are to be found at Yosemite National Park in California, where some are three thousand feet (almost one thousand meters) high.