West of the main Rocky Mountain Belt, from northern Utah to northern Arizona, the colorful and varied landscape is controlled by the so-called Colorado Plateau physiographic province. It takes its name from the Colorado River rather than the state. Most rock units are subhorizontal sedimentary rocks but here and there are folds and uplifts that have punctured the plateau. The Plateau has participated in the general deformation of western regions of the U.S. mainly by vertical uplift even as the Basin and Range was also uplifted but failing to maintain its coherence - responding instead to block faulting (see next page). Two Landsat images, accompanied by several ground photos, give the "flavor" of the flamboyantly scenic regions that comprise the Colorado Plateau.
After about 500 km (311 mi) travel westward, our trip swings to the southwest as it moves over the Colorado Plateau. The Plateau includes a small 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).
A good part 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.
We look first at what can be 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, you will truly have your body in four states simultaneous.
This false color image, taken in January, approximates some of these colors. 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.
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). These highlands blend into the Chuska Mountains to the south, just out of view..
This barren region has a very low population. Part of the scene includes the Navajo Indian Reservation. The small towns of Mexican Hat and Bluff in Utah lie along the San Juan River. At center left, this river has entrenched (deeply downcut) its meanders to produce steep canyon walls that make up the picturesque Goosenecks, shown in this photo.
6-10: What causes "goosenecks"? ANSWER Just to the west of the image, the San Juan River joins the Colorado River, upstream from the artificial Lake Powell, formed by the Glen Canyon Dam. Finally, there is a "streakiness" in much of the lower part of the image. Prevailing winds, re-enforced by joint (fractures) control of landscape erosion, cause this effect. Many people consider the Plateau the most scenic of all provinces in the U.S. because of its marvelous landforms and its colorful rocks. Many of its mainly Upper Paleozoic and Mesozoic rock units are bright reds, oranges, and yellows, whereas others are light to dark gray to brown. 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 accentuated by runoff water from Pleistocene rains and snowfalls) in the world. Its colors, from Paleozoic rocks, makes it a spectacular view that brings millions of tourists per year. However, the Grand Canyon is seemingly much less impressive when viewed obliquely from the Space Shuttle.
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:
A closer view from space from the Japanese JERS-1 satellite shows the general nature of the erosional indentations making up the canyon walls but does not reveal individual geologic units.
This next image is a generalized map of the geologic units in and around the Grand Canyon. Red denotes Paleozoic rocks; Blue defines the Mesozoic rock distribution; Green expresses the Cenozoic rocks, and yellow marks the youngest units, mostly unconsolidated rocks of Pleistocene age..
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. The National Parks at Bryce, Zion, and Canyonlands in Utah also display spectacular colored rocks. Here are three examples from space and on the ground; check the caption for location.
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. To help you visualize the landscape of this vast region, we show a ground scene of characteristic features, the San Rafael Swell (see map), a broad dome in east-central Utah, and second, the buttes that are so conspicuous in parts of southeastern Utah.
Monument Valley in southern Utah, almost a trademark for that part of the country and site of many western ("cowboy") movies, is a landscape dominated by mesas and buttes (prominences composed of flat rock stacks that are the 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
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 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 marks the southern edge of the Plateau, where erosion is cutting into its underlying sedimentary layers. Seen below is Sedona, Arizona (about 40 miles south of Flagstaff), a huge tourist attraction and often used as a backdrop in TV commercials:
This is one 'magical' place on Earth that remains best seen on the ground. No space image can do it justice.
