Glossary of Desert Terms

Alluvial Fan: A large, fan-shaped pile of sediment forming at the base of narrow canyons onto a flat plain at the foot of a mountain range.

Alluvium: Unconsolidated gravel, sand, silt and clay deposited by streams.

Anticline: An arched fold, usually in the shape of an inverted U.

Arroyo: A dry desert gully.

Bajada: A broad, sloping depositional deposit caused by the coalescing of alluvial fans.

Blowout: A depression in the land surface caused by wind erosion.

Butte: A narrow flat-topped hill of resistant rock with very steep sides. Probably formerly a mesa.

Cenozoic Era: 0 to 65 million years ago includes the Quaternary and Tertiary Periods.

Desert: Receiving less than 10 inches of precipitation annually.

Desert Pavement: A thin, surface layer of closely packed pebbles.

Desert Varnish: A hard, dark, shiny coating on rocks caused by chemical action.

Detritus: Boulders, rocks, gravel, sand, soil that has eroded from mountains over time.

Dunes: Mounds of loose sand grains shaped up by the wind.

Hogback: An eroded, steeply tilted ridge of resistant rocks with equal slopes on the sides.

Hoodoo: A column or pillar of bizarre shape caused by differential erosion on rocks of different hardness.

Jurassic Period: Age in which dinosaurs flourished, 144 to 288 million years ago.

Loess: A deposit of windblown sand and clay weakly cemented by calcite.

Mesa: Broad, flat-topped hill rounded by cliffs and capped with a resistant rock layer.

Playa: A very flat, dry lake bed of hard, mud-cracked clay.

Mesozoic Era: 66 to 245 million years ago, includes the Cretaceous, Jurassic and Triassic Periods.

Monocline: An open, step-like fold in rock over a large area.

Paleozoic Era: 245 to 570 million years ago.

Pangea: The super continent that broke apart 200 million years ago to form the present continents.

Pediment: A gently sloping surface, usually covered with gravel, the result of erosion.

Plate Tectonics: The theory that the earth's surface is divided into a few large, thick plates that are continually moving.

Precambrian Era: Prior to the Paleozoic Era, 570 millions years ago.

Semiarid: Receiving between 10 and 20 inches of precipitation annually.

Syncline: An arched fold in the shape of a U.

Triassic Period: 208 to 245 million years ago when large predatory reptiles (dinosaurs) evolved.