Canyon Rocks & Minerals

No Collecting Rock Specimens

Collecting rock specimens in Black Canyon of the Gunnison National Park is illegal.

 

Most of the rocks exposed along the length of the Black Canyon are Precambrian in age (older than 500 million years) and are either metamorphic or igneous. Some sedimentary layers are also evident along the north rim of Black Canyon. Rocks found in the canyon have a wide variety of minerals. Here is a brief look at some of them and where they may be found.

 

Left image
Geologic map of Black Canyon and nearby vicinity. Precambrian gneiss and schists are shown in pink, light brown, and grey in the canyon.
Credit: U.S. Geological Survey

Right image
Topography of Black Canyon and nearby vicinity
Credit: Image courtesy of Google Earth

 

A sample of gneiss

NPS/A. Fitzgerald

Metamorphic Rocks

The word "metamorphic" originates from the Greek language and means to transform or change. Metamorphic rocks usually start out as sedimentary, or igneous rock, but when buried deep in the earth, intense heat and pressure "cooks" or bakes" them into a completely new rock.

Heat and pressure are the two most important parts of this process, but time also plays a role; the longer the rock has been baked and squeezed, the greater the changes. Rock is usually buried deep within the Earth's crust (6–8 miles or 9.5–12.9 km) before temperatures and pressures are high enough to melt and change their physical and chemical composition. Black Canyon's metamorphic rocks have been altered to the point that little trace of the original rock remains. However, geologists suspect that the original rocks, or protoliths were sands, mud and volcanic debris that accumulated on the floor of an ancient sea. The time of metamorphism is estimated at 1.7 to 1.9 billion years ago.

Gneiss and schist are examples of metamorphic rocks found in the Black Canyon. These rocks blend from one to another because of variations in the heat and pressure which occurred when some rocks were buried deeper than others.

 

Learn More about Metamorphic Rocks

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  Gneiss

  Gneiss represents rock that underwent some of the most advanced stages of metamorphosis.

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  Schist

  Although still considered metamorphic, schists have been altered less because of the lower pressures and temperatures.

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  Metamorphic Rocks

  Learn more about metamorphic rocks and what NPS sites have them.

 

A sample of pegmatite.

NPS/A. Fitzgerald

Igneous Rocks

Igneous rocks (meaning "fire-born") cooled from a molten rock, or magma, deep beneath the surface of the earth. If magma cools before it reaches the surface, it is called intrusive. Magma that reaches the surface, as in a volcanic eruption, is referred to as extrusive. Examples of igneous rocks in the Black Canyon are intrusive rocks. Here, the magma was pushed into the existing metamorphic rock and never reached the Earth's surface. Igneous intrusive rocks in Black Canyon leans mostly towards a granite composition - meaning it is more silicic (high in silicia).

Quartz monzonite, an intrusive-igneous rock, makes up the Curecanti Needle and intrusions from Rock Point to Warner Point. The striking, pinkish banding evident throughout the canyon, and most well-known on the Painted Wall, is pegmatite—granite with huge crystals.

 

Learn More about Igneous Rocks

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  Quartz Monzonite

  Two types of quartz monzonite, an igneous-intrusive rock, are found in the park.

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  Pegmatite

  Learn about those segments "painting" the walls of Black Canyon.

 

Resources

Black Canyon/Curecanti Online Bookstore
A variety of titles dealing specifically with the geology of the Black Canyon and Colorado in general, are available for online purchase.

The Interior of the Earth
Online Edition by Eugene C. Robertson
This publication, available through the U.S. Geological Service, gives an excellent introduction to what lies below the surface of the Earth.

Natural Gemstones
Also from the USGS, this page provides an in-depth look at gemstones from around the country.

Hansen, Wallace R. 1965. THE BLACK CANYON OF THE GUNNISON: Today and Yesterday. U.S. Geological Survey Bulletin 1191. USGS: Geological Survey Bulletin 1191 (nps.gov)