periods. Succulent xerophytes include cacti, which have shallow and often widespreading root systems that can take up soil moisture from even the lightest rainfall. Cacti are leafless; their succulent pads are actually stems. These stems swell with stored moisture in spring, and they slowly and economically metabolize that moisture throughout the dry part of the year. When much of the moisture has been used, the stems shrink and become wrinkled, but unlike nonsucculent xerophytes, cacti do not go dormant when stressed by drought.
Nonsucculent xerophytes survive long periods of drought by various means other than water storage. The deep root systems and special cellular structures of some of these plants are able to obtain moisture from the soil long after the rains have fallen. Other characteristics of nonsucculent xerophytes that help to prevent moisture loss and excessive heating of plant tissues include:
vertical orientation of leaves, which reduces the surface area exposed directly to sunlight
dense matted hairs on leaves and/or stems or a resinous coating
a grayish pigment on leaves and stems
very small pores on the leaves
wide spacing of plants
Some plants conserve energy and moisture by curling their leaves or even dropping them. If there is not enough moisture to support the plant, then all but perhaps a single branch will die back, or the entire above-ground plant may die, all of its energies being diverted to preserving the life-sustaining root system. Manyxerophytes have rigid, woody, spiny branches, which, when combined with hairy or resinous foliage, discourage browsing animals from eating them.
In most mountainous regions in the Western U.S., plants are fairly evenly separated into belts, or zones, that vary with elevation, temperature and precipitation. However, the plant communities of the Colorado Plateau are not uniform in their patterns, and likewise the land itself is highly varied, containing deep and sometimes moist canyons, parched mesas and desert flats, vast expanses of naked stone, and sheer cliffs devoid of vegetation and soil.
For example, the pinyon-juniper woodland is one of the most common plant communities visitors will encounter, but this woodland does not grow at any typical elevation; rather, it grows where local environmental conditions are suitable to support it. In Zion National Park, for example, one will find this woodland growing at 4000 feet, while near Canyonlands it is found above 7000. Where a canyon has been eroded into the plateau, one may also find a pinyon-juniper woodland, while above the canyon only a scattering of shrubs may exist.
Bristlecone pine below the rim of the Paunsaugunt Plateau
Zion National Park
In the far southwestern corner of Utah, very near where the Colorado Plateau meets the mountains and valleys of the Great Basin, lies Zion National Park, one of the gems of the national park system.
Within its 147,000 acres are landscapes of incredible beauty and infinite diversity. Sculptured cliffs towering thousands of feet above deeply incised canyons display a kaleidoscope of pastel hues, their color and brilliance changing before a viewer’s eyes with the changing light of the day.
As the seasons change, so does the face of Zion. Spring brings the melting of snow atop the plateaus. Where runoff waters reach the brink of the great cliffs, hundreds of waterfalls are born. Bright green leaves adorn the trees and shrubs, and wildflowers explode in incomparable color. Streambeds run bank-full until the searing heat and dryness of approaching summer sap their vigor.
With the onset of autumn, broadleaf trees paint the landscape with brilliant reds and golds that vie with the colorful cliffs for the viewers’ attention. The grip of winter blankets the land with its envelope of white, and decorates springs and seeps with icicle curtains.
Not only do the landscapes of Zion change with the passing seasons, but the land itself is in a state of constant change. Most of this change is imperceptible in a human lifetime, but at times the change is dramatic and obvious, as in rockfalls and landslides.
Zion National Park encompasses that part of the vast Markagunt Plateau, known as the Kolob Terrace, that forms the Virgin River watershed, southwest Utah’s largest tributary to the Colorado River. The Hurricane Cliffs bound the plateau on the west, forming the boundary between two major physiographic provinces: the Basin and Range Province to the west, and the Colorado Plateau stretching eastward to the Rocky Mountains.
The Markagunt is one of the most extensive of Utah’s high plateaus, roughly 70 by 30 miles. The southern half of its surface is incised by tributaries of the Virgin River. These tributary canyons, combined with the nature of the sedimentary rock layers through which they have eroded, are responsible for the magnificent scenery that visitors from all corners of the globe come to enjoy.
The North Fork of the Virgin has created a deep and narrow canyon of incomparable beauty. At its widest point, one-third mile separates the canyon walls, and at its narrowest, only 20 feet or so. Imposing buttes and towering crags crown the canyon’s cliffs, and from below they appear to be majestic mountain peaks. From the heights of the gently contoured plateau, however, viewers gain a different perspective of them. Up there, one quickly notices that the tops of these buttes and towering crags were at one time parts of the continuous level landscape of the plateau. They are simply now isolated from it by erosion.
Geologists have subdivided the Colorado Plateau physiographic province into a number of distinct units. Parts of Zion and Bryce lie within the Grand Staircase section, near the southern margin of the High Plateaus. True to its name, the Grand Staircase rises in a series of varicolored cliffs and broad plateaus from the north rim of the Grand Canyon to the Pink Cliffs high on the flanks of the Markagunt, Paunsaugunt and Aquarius plateaus. Each “step” contains vast wooded plateaus, and each “riser” exposes varicolored cliffs. The belt of cliffs forming the “riser” in Zion is the White Cliffs, composed of the Park’s dominant sedimentary rock layer, the Navajo Sandstone. The Vermilion Cliffs, composed of the Moenave and Kayenta formations, outcrop along the flanks of lower Zion Canyon. The youngest rise in this series of steps is the one at the edge of the highest of the southern High Plateaus—the Pink Cliffs of Cedar Breaks and Bryce Canyon.
Human History of Zion
Mankind has been in the Zion landscape from time immemorial. We know that the Ancestral Puebloans (formerly known as the Anasazi) dwelled here, attested to by their cliff houses in Parunuweap (“water that roars”) Canyon, their rock art, the abundance of chipping sites throughout the Park, and caves that bear reminders of ancient fires. Archaeologists also believe that people of the Fremont culture may have lived in the northern reaches of the Park.
Prehistoric people lived here from about 500 until their departure around 1200 to 1300. During that time they evolved from hunter-gatherers into farmers of corn, squash, and beans. Following their departure, the land we know as Zion remained largely unoccupied until the arrival of Mormon settlers during the mid-19th century. However, during that time scattered bands of Piutes inhabited the upper Virgin River valley, camping in areas that were later the sites of Mormon settlements, some of which remain as towns today. The Piutes utilized the Zion region for seasonal hunting and gathering forays, and some bands farmed in the valleys outside the Park. They did not, however, venture very far into the canyons.
It was the Piutes that early travelers and explorers encountered in southwest Utah. They contributed their geographical knowledge of the region, but were of little aid when Mormons later explored the forbidden (according to Piute superstition) depths of Zion Canyon. In 1850 a party of
