The River Below

The Colorado River flows 277 river miles (446 km)

from Lees Ferry to the Grand Wash Cliffs, the 

accepted beginning and end of Grand Canyon. 

Hidden in the narrow Inner Gorge, the river is 

visible from only a few spots along the rim.

From the rim, the river looks puny, yet it averages 

300 feet (90 m) wide and features a series of 

fierce rapids. From its origins high in the 

Colorado Rockies, the river drops more than 

12,000 feet (3,700 m) and passes through a series 

of canyons, including Grand Canyon, on its 

1,450-mile (2,300 km) journey to the Gulf of 

California.

The Landscape

The grandeur of Grand Canyon lies not only in 

its size, but also in the beauty of its landscape. 

In this respect, Grand Canyon shares many 

characteristics with its neighbors—Zion, Bryce, 

Canyonlands, Arches, and Capitol Reef national 

parks. Like Grand Canyon, these neighboring 

parks lie within the geologic province known 

as the Colorado Plateau, a region characterized 

by mostly flat-lying sedimentary rocks that have 

been raised thousands of feet above sea level, 

then carved by erosion.

Landforms here are beautifully sculpted and 

well exposed due, in part, to climate. The semiarid climate that predominates in the Southwest 

means that instead of tree-covered slopes and 

thick soils, bedrock is at the surface. Therefore, 

rain does not soak into the ground; instead it 

runs off in huge floods carrying away grains 

of rock. Cycles of freezing and thawing in the 

winter widen cracks in the rocks, eventually 

producing rockfalls. Soft layers erode more 

rapidly undermining the hard layers above. Bit 

by bit, flash flood by flash flood, and rock fall by 

rock fall, the canyon continues to grow.

Each of the rock units in the canyon erodes 

in its own manner, yielding the characteristic 

stepped-pyramid look of the canyon. Shales 

erode to slopes, while harder sandstones and 

limestones tend to form cliffs. The extremely 

hard metamorphic rocks at the bottom of the 

canyon produce the steep-walled and narrow 

Inner Gorge, as these rocks are more resistant to 

erosion than the softer sedimentary rocks above.

Color is also an important feature of this 

landscape. Many of these colors are due to the 

presence of small amounts of iron oxides and 

other minerals that are either in the rock itself or 

stain the surface and mask the true color of the 

rock.

The name Colorado is derived from Spanish for 

reddish, reflecting the heavy sediment loads the 

river once transported. Dams now bracket Grand

Canyon—Glen Canyon Dam (Lake Powell) 

upstream and Hoover Dam (Lake Mead) 

downstream. As a result of these dams, the 

dynamics of the Colorado River through Grand 

Canyon changed dramatically. Gone are the large 

annual floods that carried hundreds of thousands 

of tons of sediment through the canyon each day.

Today, the Colorado is seldom its natural 

muddy red-brown color. Only when tributaries 

downstream from Glen Canyon Dam, such as 

the Paria and Little Colorado rivers, contribute 

significant amounts of sediment during flash 

floods or spring snowmelt, does the river change 

from clear blue-green to its natural reddishbrown.

The North Rim

The North Rim and the South Rim are only 

separated by ten miles (16 km) as the raven flies. 

Although it is not apparent, the north wall of 

the canyon rises a thousand feet (305 m) higher 

than the South Rim, giving the North Rim nearly 

twice the annual precipitation as South Rim. This 

considerable difference in elevation results from 

the fact that the apparently flat-lying rocks of the 

Kaibab Plateau are dipping gently to the south.

Toroweap Overlook in western Grand Canyon offers 

visitors a stunning view of the Colorado River. 

Expansive views from Cape Royal on the North Rim

Journey Through Time:

Grand Canyon Geology

printed on 100% recycled paper 0915

National Park Service

U.S. Department of the Interior

Grand Canyon National Park
Canyon Origins

Although the origin of Grand Canyon is complex 

and not totally deciphered, the forces that 

shaped it are well understood. Grand Canyon 

is the result of erosion, specifically incision by 

a river into a high, arid plateau. The Colorado 

River carved the depth of the canyon as it cut its 

way through the Kaibab Plateau which is more 

than 7,000 feet (2,100 m) above sea level. Side 

canyons, scoured by summer thunderstorms 

and winter snow melt, produce much of Grand 

Canyon’s 10–16-mile (16–22 km) width. 

Compared to the rocks exposed in its walls, 

Grand Canyon is geologically young. Excavation 

of the canyon occurred within the last six 

million years or so. The question of how the 

Colorado River evolved its present course is 

still unresolved, even though geologists have 

hypothesized for years about how the river first 

established its path across the plateau and carved 

this immense chasm. Much of the uncertainty 

regarding the exact age and history of the canyon 

centers on the reality that we have only scattered 

bits of evidence to reconstruct its history and 

to precisely date its origin. The history of the 

Colorado River is complex and will be the 

subject of geologic research for years to come.

Geologic Cross Section of Grand Canyon

Vishnu basement rocks line the walls of the Inner George.

The Geologic Record as Told by the Rocks 

Nowhere on this planet are the scope of geologic 

time and the power of geologic processes as 

superbly and beautifully exposed as in these 

canyon walls. Rocks equivalent to many of these 

strata may be found scattered throughout the 

United States and flowing water has sculpted 

other landscapes. Yet, at Grand Canyon, a 

remarkable geologic assemblage is exposed in 

sequence and intact in an amazing erosional 

landscape.

The canyon walls reach about 5,000 feet 

(1,500 m) below the rim to the river. The 

thickness of all Grand Canyon rocks, if present 

in one spot, would total more than 15,000 feet 

(4,600 m). Some rock units, however, appear only 

in some parts of the canyon. The strata of Grand 

Canyon do not present a continuous record of 

Earth’s history. Some rock layers eroded away 

before newer layers were deposited on top, 

producing unconformities, millions of years of 

missing time, and unknown geologic stories.

Each rock layer represents a period when a 

particular environment of deposition prevailed. 

For example, the Kaibab Formation, the rock 

that makes the canyon rims, is the youngest of 

Grand Canyon’s layers. The Kaibab Formation 

formed in shallow, warm seas about 270 million 

years ago, a bit before dinosaurs roamed the 

Earth. Below the Kaibab Formation caprock, the 

strata become progressively older. 

The oldest rocks lie more than 3,000 feet (900 m) 

beneath the rim in the walls of the Inner Gorge. 

The Vishnu basement rocks consist of ancient 

igneous and metamorphic rocks that formed 

deep in the Earth when island arcs collided with 

the continental mass. These crystalline rocks—

schist, gneiss, and granite—are very different 

in origin and structure than the sedimentary 

rocks above them. The Vishnu basement rocks, 

including Vishnu Schist, are between 1,840 and 

1,680 million years old. 

1 . Kaibab Formation . . . . . . . . . . . . . . . . . . 270 my

2 . Toroweap Formation . . . . . . . . . . . . . . . . 273 my

3 . Coconino Sandstone . . . . . . . . . . . . . . . . 275 my

4 . Hermit Formation . . . . . . . . . . . . . . . . . . 280 my

5 . Supai Group . . . . . . . . . . . . . . . . . . 315–285 my

6 . Redwall Limestone . . . . . . . . . . . . . . . . . 340 my

7 . Temple Butte Formation . . . . . . . . . . . . . 385 my

8 . Muav Limestone . . . . . . . . . . . . . . . . . . . 505 my

9 . Bright Angel Shale . . . . . . . . . . . . . . . . . . 515 my

10 . Tapeats Sandstone . . . . . . . . . . . . . . . . . 525 my

11 . Grand Canyon Supergroup . . . 1,250–650 my

12 . Vishnu basement rocks . . . . 1,840–1,680 my

printed on 100% recycled paper 0915

123456789

10

11

12