Geologic Feature


Marble is a metamorphic rock that forms when limestone is subjected to heat and pressure underground, for example during the regional shifting of the Earth's crust or during volcanic activity.


A sedimentary rock composed primarily of calcium carbonate, colloquially known as calcite. Limestone can form in two ways: the first occurs when organic remains, such as coral and shell, accumulate as particulate debris on the ocean floor over time. The second method is the chemical precipitation of calcium carbonate, which is when calcium carbonate that may be dissolved in a watery landscapes precipitates, or is removed, from its marine solution to settle onto the ocean floor. The water in which limestone forms is often warm and calm, so that the organic remains or chemical depositions are able to accumulate undisturbed over time, ultimately compressing themselves into layers of limestone under their own weight. As the earth ages, limestone environments that were formerly under water become exposed as prehistoric bodies of water recede. Some of the most extraordinary limestone deposits can also be found underground in caves, like those found throughout the Southwestern United States.

lava butte

Also known as volcanic plugs or necks, lava buttes form when magma hardens within a vent of an active volcano. Erosion can remove the surrounding rock, leaving the erosion-resistant plug behind, producing a distinctive, upstanding landform.

Shiprock, New Mexico, is one example of a lava plug.


Magma, or molten rock, rising in liquid form onto the earth's surface, usually by volcanic eruption. The term also applies to the solidified rock that is formed once molten lava has cooled.


A crack or cleft in a rock surface. This fissure can occur in joints between rock formations or in faults between tectonic plates.

earth's crust

The earth is made of multiple layers of hardened and liquid rocks, which include, moving from the exterior of the planet toward the interior, the crust, mantle, outer core, and inner core. The crust is the hardened outer layer of rock composed primarily of silicate and iron.


A general term referring to a small hill, mound, or knoll above the ground in any natural environment.


In general use, a tributary is a stream that flows into a river or a lake. For instance, the important Colorado river has many tributaries, such as the Little Colorado River, San Juan River, Santa Cruz River, and the San Pedro River. However, in Tony Hillerman's 1970 Navajo detective novel THE BLESSING WAY, the characters travel through a canyon system which includes smaller canyons (tributaries) branching off from a larger one.


A long and wide trench that cuts into soft rock or sediment. Gullies normally occur in areas where the ground surface has been exposed to fire, the effects of climate change, or human activity. Without plants, especially their root systems, rainfall can cause the sediment to erode as water moves swiftly over the surface of the earth and, via friction, removes particulate matter.


Butte is a French term meaning “hillock,” which is generally a very high hill with a flat top and steep sides. Buttes usually are bordered by flat plains and are common geologic features in the semi-arid American Southwest.


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