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 area of debris often caused by the blending of several 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.
