According to park staff:
About 60 million years ago, a small area of land uplifted and brought 1.8 billion year old metamorphic rock to high elevations. This is called the Gunnison Uplift. About 30 million years ago, large volcanoes erupted on either side of this uplift, burying it in volcanic rock. Then, as early as two million years ago, the Gunnison River began flowing in force. The river and time eroded all the volcanic rock and cut a deep canyon in the metamorphic rock below.
Rock Point view of Black Canyon of the Gunnison National Park / NPS file
Those are what you might call the CliffsNotes version of Black Canyon of the Gunnison National Park’s geologic creation. But let’s delve a little deeper into this steep, deep, and narrow canyon’s formation, beginning with this national park’s location.
This national park sits near the edge of the Colorado Plateau and next to the Southern Rocky Mountains physiographic provinces. A physiographic province is a geographic region with a distinct set of landforms and geological characteristics. The Colorado Plateau physiographic province covers 240,000 square miles (621,597 sq. km) of Four Corners landscape spanning Arizona, Utah, Colorado, and New Mexico. Volcanic landscape, buttes, canyons, and plateaus dominate terrain. Elevations range from 2,000 feet (610 m) to 13,000 feet (3,962 m).
Unlike the Grand Canyon in Arizona, Black Canyon of the Gunnison is not very wide but it is quite deep over its entire length, with an average depth of 2,000 feet (610 m). The deepest portion of the canyon is 2,722 feet (829 m) north of Warner Point. The Gunnison River has a much steeper gradient than the Colorado River, with an average drop of 43 feet (13 m) per mile versus 7.5 feet (2.3 m) per mile. The Gunnison’s erosive power gives the depth you see to the canyon, but this waterway did not always have the erosive cutting power it does today.
Gneiss is one of the metamorphic rocks composing the canyon walls of Black Canyon of the Gunnison National Park / NPS - A. Fitzgerald
The real action didn’t begin until the end of the Gunnison Uplift, about 60 million years ago during a period of mountain building called the Laramide Orogeny. Volcanoes formed and erupted north and south of the Gunnison Uplift, covering the landscape with thousands of feet of ash and volcanic debris. The weight of all this caused the area to sag and create a valley, and the Gunnison River flowed through these soft Mesozoic and Cenozoic volcanic and sedimentary rocks 15 million years ago. Once the river eroded through these soft soils, it hit ancient metamorphic and igneous bedrock almost 2 billion years old.
As you look at this ancient rock, particularly in the area known as the Painted Wall, you will see pink-ish veins of another rock against the darker metamorphic gneisses and schists. Metamorphic rocks are created from intense heat and pressure that bakes, squeezes, stretches and otherwise alters the minerals within sedimentary and igneous rocks. Those pink veins are pegmatite.
According to park staff:
Pegmatite refers to igneous rock with very coarse texture and unusually large, intergrown crystals. It consists mostly of quartz, feldspar, and mica. As magma cools and solidifies, water becomes concentrated. This concentration makes the magma more fluid and easier to squeeze, like toothpaste out of the tube, into the surrounding rock. The crystals can be very large—up to 6 feet (2 m) in length.
Pegmatite intrusions, Black Canyon of the Gunnison National Park / NPS - Kat Connelly
Pegmatite is abundant throughout Black Canyon. It is found in the form of large bodies, stripes, and "dikes." Since it is more resistant to erosion, it sticks out boldly against less resistant gneiss and schist. Potassium (K) feldspar gives this pegmatite its pink shade. Large outcroppings are visible on the Painted Wall, upstream from East Portal, or at Kneeling Camel on the north rim of Black Canyon.
The Gunnison River continues to cut down into the canyon along with other erosive forces such as wind, rain, frost heaving, and rockslides.
For a more detailed description of Black Canyon of the Gunnison National Park’s geology, as well as that of nearby Curecanti National Recreation Area, you can read the National Park Service’s 2005 Geologic Resource Evaluation Report.
Traveler’s Note: You will find some interesting rocks along any of the trails you hike within this national park. Please leave what you find for others to see. Collecting rock specimens in Black Canyon of the Gunnison National Park or Curecanti National Recreation Area is illegal.
