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 without folding even as the Basin and Range (see next page) was also uplifted but failed by general faulting of complexly deformed Paleozoic rocks. 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 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. 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".
We look first 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. 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. 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.
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. 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.
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 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):
The writer scrounged the Internet looking for some picture from space that showed differentiable layers. Only this showed up:
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 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 (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.
Zion National Park:
The cross-bedding within the Cretaceous Navajo Formation is evident in this photo, and is shown in more detail (bedding planes emphasized by optical spatial filtering) in the subscene taken from the photo:
And the Canyonlands Park:
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, first, the San Rafael Swell (see image on page 5-5), 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 ( 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 ground photo of a single butte, followed by a small part of Monument Valley as seen from space, and then a perspective view made from ASTER data.
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'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.
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.
