Geology

The surface of the Earth is broken into several plates, some entirely oceanic, some comprised of both continental land masses and oceanic crust. Convection currents in the molten portion of the planet below the surface slowly move these plates toward and away from each other. The movements of the plates create strains of extension and compression on the continents, which can cause some portions of the surface of the land to rise while adjacent land falls. In conjunction with the erosional forces of water and wind, these processes have created the mountains, valleys, plateaus, and canyons of the southwestern United States. Sometimes the molten material rises toward the surface, where it might be released as cinders and ash or as liquid flows of lava. The volcanoes and related igneous rock formations further diversify the surface features of the Desert Southwest. Additionally, shallow seas once covered portions of the Southwest. Within these seas, limestone reefs were formed, and halite and gypsum were deposited. These features were exposed as the seas retreated and the land rose and was eroded by wind and water. This diversity of surface features provides the foundation for a corresponding diversity of biotic communities, from desert scrub and desert grasslands to montane woodlands and forests.

• Basin and Range

• Volcanic Features

• White Sands National Monument

• Grand Canyon National Park

• Capitan Reef (Guadalupe Mountains and Carlsbad Caverns National Parks)

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