After about 500 km (311 mi) travel westward, our trip swings to the southwest as it moves over the Colorado Plateau. The Plateau includes part of western Colorado and northwestern New Mexico, much of northern Arizona and a substantial part of Utah. Its principal geographic locations are shown in the first map below and its physiographic subdivisions in the second map map:
The Colorado Plateau has participated in the general uplift of the interior western U.S. since the Cretaceous. Unlike its eastern neighbor, the southern Rocky Mountains, this segment of the continental crust was thermally heated and subjected to vertical uplift without extensive folding (there are a few small folded warps and some faulting). Thus the "trademark" of the Plateau is the dominance of flat-lying (near horizontal) sedimentary rocks, largely exposed and often without much vegetation. Many of these rock units, ranging from Paleozoic to Cenozoic in age, are colored in shades of red, orange, yellow, and brown. The vistas of bright-colored layers means that the Colorado Plateau probably contains more photogenic scenery than any other part of North America.
This perspective drawing, aided by satellite imagery, gives a good overview of the Colorado Plateau, as well as the Basin and Range to the west:
The Plateau is conspicuous to astronauts in orbit because much of its terrain is brightly colored in reds and browns (north is to the right):
Much of the Plateau is seen in this mosaic of several Landsat images:
But it helps to examine the Plateau in the context of surrounding provinces. We saw much of the western United States in a HCMM image on the previous page. Now look at this even larger coverage found in a MODIS image:
The central area with reds and browns make up the Colorado Plateau. Most of the Southern Rocky Mountains appears to the east. Part of the next province we will visit - the Basin and Range is displayed in much of Utah and Southern Arizona. The top of the image shows much of southern Wyoming which is commonly assigned to the Central Rocky Mountains. In the northwest corner of Utah. The large white patch in Utah's northwest (see state outline in black) is the Great Salt Lake Desert, whose saline deposits form a smooth flat surface on which supercharged racing cars have broken international speed records. One surprise: the Grand Canyon (see below) is almost "invisible".
Many people consider the Plateau the most scenic of all provinces in the U.S. because of its marvelous landforms and its colorful rocks. Some of its mainly Upper Paleozoic and Mesozoic rock units are bright reds, oranges, and yellows, whereas others are light to dark gray to brown. Because of their scenic value, these rocks are a major reason for the establishment of numerous national and state parks in the Colorado Plateau:
If one reaches the Plateau by traveling west along Interstate 70, the first large town encountered is Grand Junction, Colorado, near the Colorado National Monument. This town now has about 50,000 residents and dominates the Grand Valley:
Grand Junction lies in a valley north of the Uncompaghre Plateau that is an uplift of Mesozoic flat rocks overlying a segment of the Ancestral Rocky Mountains. Here is a space image; its top part is the east end of the Tavaputs Plateau that exposes the Book Cliffs at its south end:
In southwestern Colorado, within the Plateau, is the Mesa Verde National Monument. Here is the region from space. Beneath it is a photo of Indian cliff dwellings for which the Monument is famed:
We look next at what is called the Four Corners area of the Plateau. There is a plain benchmark at the exact spot where the four states - Colorado, Utah, Arizona, New Mexico - touch. If you straddle this marker in a supine pose, you will truly have your body in four states simultaneously.
The Landsat scene shown below includes the Four Corners - the only place in the U.S. in which that many states touch each other at one point. Unfortunately, we can't discretely identify the point, but it lies about 30% up and 15% in from the lower right corner of the image.
This false color image, taken in January, approximates some of the colors seen on the ground. At this time of year the sparse vegetative cover of sage, mesquite, and grasses does not produce a typical red signature, so that the surface tones are entirely those of rock and soil. Although not discernible in the image, the Plateau rocks are almost everywhere still in the subhorizontal positions, in which they were deposited as sediments. Because they erode along steep faces or scarps, where cap rock is hard, the layers stack like steps to form plateaus, mesas, and buttes. The Gothic Mesas, just to the right of image center, are typical. Monument Valley begins near the lower left corner. The Plateau has participated in the general deformation of the West chiefly by uplifting without folding. However, Combs Ridge, a prominent monocline (like the Waterpocket Fold) is evident about 15-20% in from the left edge of the image. Near the bottom right corner are the snow-capped Carrizo Mountains, partially volcanic in origin, which rises at Pastora Peak to 2,870 meters (9,414 ft). This barren region has a very low population. Part of the above scene includes the Navajo Indian Reservation. The small towns of Mexican Hat and Bluff in Utah lie along the San Juan River. There is a "streakiness" in much of the lower part of the image. Prevailing winds, re-enforced by joint (fractures) control of landscape erosion, produce this effect.
Another Landsat image covers the region to the west of the previous image. Locate Comb Ridge. To its west are the entrenched meanders of the San Juan River. These have been named the Goosenecks.
This IKONOS image concentrates on the Goosenecks, also seen in a low altitude oblique aerial photo:
In Section 2, page 2-3, you have already examined in some detail one small area in the Plateau, the Waterpocket Fold in the Capitol Reef National Monument. That fold is a monocline (only one limb inclined); such structures are scattered over the Colorado Plateau, often making up a landform called a hogback, such as pictured here:
Just to the west of the image, the San Juan River joins the Colorado River, upstream from the artificial Lake Powell. This, the second largest of its kind in the U.S., results from flooding of the River behind the Glen Canyon Dam, next to Page, Arizona. The area has become a popular tourist destination, with tours by boat around the lake (one can rent a movable houseboat also) This is Lake Powell, seen from Landsat and from on the lake itself.
Downstream from Page, the Colorado River widens its valley and becomes entrenched. This valley, known as Marble Canyon, is a popular tourist attraction. Here it is shown from space and in an aerial photo:
To the southwest of this scene, the Grand Canyon, the most famous feature in the Plateau, exposes typical, multi-colored units. Being several hundred kilometers long, up to 30 km (18 miles) wide, and as deep as 1.6 km (1 mile) deep, this is the largest canyon in terms of volume of excavation (which was accelerated by runoff water from Pleistocene rains and snowfalls) in the world. Yet it is a recent phenomenon, having been cut into the Plateau as the land rose only in the last 6 million years. Its colors, from Paleozoic rocks, makes it a spectacular view that brings millions of tourists per year.
A false color Landsat subscene places this mile-deep gouge into context with the Colorado plateau. The eastern part of the Grand Canyon is well displayed in this Landsat-1 image:
Considering the variety of layered rocks representing 1 Mesozoic Formation and 14 Paleozoic formations, it is surprising that these do not appear as thin bands in the Landsat images and especially the JERS image. Here is an IKONOS image at even higher resolution and again layering - the hallmark of the Grand Canyon as the best exposed stratigraphic sequence in the world - is totally absent (but the pinkish color may be contributed by some units):
A geologic map of the Grand Canyon brings out the effects of layers of different ages, since the map uses different colors to differentiate major stratigraphic intervals:
So, why does space imagery fail to distinguish these layers (the Formations involved are discussed below)? Perhaps this photo provides an explanation:
One is struck immediately by the almost uniform reds that seem to color the rocks from the Kaibab Plateau to the gorge through which the Colorado River flows. Yet, in hand specimens, the various units have a range of colors. What seems to have happened is that over the eons, the exposed cliffs and benched slopes have acquired iron staining that imposes uniformity of surface coloration. Often though, standing on the rim, at least some of the various formations can be distinguished by eyeballing the colors. But, the surfaces of these formations do have less color variation than, say, the Waterpocket Fold we examined in Section 2.The bottom of the Grand Canyon is a common destination for the intrepid, who either walk down and up some 5000 ft vertically along a trail carved into the canyonwalls or make the trip on the back of a sure-footed burro. The floor of the canyon is generally narrow but, while very hot in summer, has been inhabited by Indian tribes for centuries before its discovery by explorers and its first passage by boat by Wesley Powell, the geologist-explorer in the 1880s. This next image is a high resolution image made by the IKONOS satellite of the darker Precambrian schists and gneisses that rise above the floor of the Grand Canyon.
The horizontal Paleozoic sedimentary rocks rest unconformably on tilted Proterozoic metasedimentary rocks that in turn lie on Archaean rocks dominated by the Vishnu schists. These are exposed in the lower part of the canyon walls seen in this ground photo:
The Grand Canyon continues westward towards southern California but ends just east of Nevada. As it crosses that state, it has been dammed south of Las Vegas (see next page) at Hoover Dam (also called Boulder Dam), behind which Lake Mead has developed. All this including the western Grand Canyon is displayed in this Landsat-1 image
The geologic formations at the Grand Canyon are considered the best exposed type section (a section denotes the sequence of successive age units going upwards from oldest to youngest) in North America. First note this sketch with the main units on the right side of the block diagram. The second figure gives details about the formations so exposed.
Most of these units can be found elsewhere on the Plateau. They are often distinctly colored, making them into "must see" places that attract tourists - some to National Parks. The rocks of the Plateau tend to tilt northward from the Grand Canyon. Most of these are Mesozoic sandstones and shales. This diagram indicates the general structure of this part of the Plateau:
As seen from space:
The National Parks at Bryce, Zion (in southwest Utah, respectively east and southeast of Cedar City), and Canyonlands (in southeast Utah west of Moab) also display spectacular colored rocks. Here are examples from space and on the ground; check the caption for identity of Park.
The soft claystones and sandstones making up the Bryce outcrops, carved into marvelous figurines by water erosion, have distinctive red and yellow colors. These are difficult to capture photographically but this is a good example.
Zion National Park is well known for the sandstone units that show distinct cross-bedding.
The rocks in the above satellite image show prominent joints - in fact, better termed megajoints. This higher resolution satellite image shows these in detail.
Here is the valley that exposes these units:
The cross-bedding within the Cretaceous Navajo Formation is evident in these photos:
And the Canyonlands Park:
Similar to Canyonlands is Canyon de Chelly, in Arizona, which is noted for its Indian cliff dwellings.
In Utah is another member of the National Park system, the Arches National Monument:
Monument Valley in southern Utah, almost a trademark for that part of the country and site of many western ("cowboy") movies (it was John Wayne's favorite locale), is a landscape dominated by mesas and buttes (both defined as prominences composed of flat rock stacks that are the topographic remnants of stripping away of most of the higher layers from an earlier plateau cover). Here is a small part of Monument Valley as seen from space, a ground photo of a butte and its neighbors, and a panorami photo that shows a cluster of buttes.
Moving now to the south, here is a satellite image that shows recent volcanism in northern Arizona. This scene contains cinder cones within the San Francisco Volcanic Field.
Some of these cinder cones are young, with the last eruption being witnessed by local Indians in the 11th century AD. Two of the best known cones are Sunset Crater and SP crater, shown here;
The field can be pictured as a perspective view, made from an ASTER image
The San Francisco Peaks are actually remnants of an older stratocone complex, now breached by erosion. The highest of these is Mount Humphreys, rising over 12000 feet.
In the vast region of northeast Arizona and a bit of Utah that makes up the Navajo (Indian) Reservation are the Hopi Buttes shown in the lower right corner of this Landsat image:
This space image settles on the Hopi Buttes, one of which is seen in the ground photo below it.
The Hopi Buttes are actually volcanic necks and diatremes that have been exposed as pinnacles after erosion has removed the surrounding rocks. A diatreme usually has a maar at its surface. The maar is an explosion crater formed when volcanic material interacts with shallow ground water which produces steam that blows out the rock. Here is a schematic of a diatreme/maar complex and one of the maars at Hopi Buttes:
The Landsat scene also contains the Painted Desert, noted for its colorful sedimentary rock layers:
The writer's (NMS) favorite spot in all of the western U.S. is along the Mogollon Rim (a popular locale for Zane Grey western novels) which makes up the southern edge of the Plateau. The Rim's face is a nearly continuous cliff where erosion is cutting into the Plateau's underlying sedimentary layers (mostly Mesozoic Formations). Seen below is Sedona, Arizona (about 40 miles south of Flagstaff), a huge tourist attraction and often used as a backdrop in TV commercials. Junipers are the dominant tree. This is a view looking west over the town:
This high altitude aerial photo shows the landscape around Sedona.
And here is Sedona as seen by Quickbird (Google Earth):
This is one 'magical' place on Earth that remains best seen on the ground. No space image can do it full justice.