The Grand Canyon epitomizes the Colorado Plateau, an area that has been called the "land of color and canyons." The Plateau can be thought of as an elevated, northward-tilted saucer. It is characterized by its high elevation and arid to semi-arid climate. The Colorado Plateau has developed great relief through the erosive action of high-gradient, swift-flowing rivers that have downcut and incised the plateau. Approximately 90 percent of the plateau is drained by the Colorado River and its tributaries.
The region has conspicuous but irregular vegetation zones. The woodland zone in the most extensive, dominated by what is often called a pygmy forest of pinyon pine (Pinus edulis) and several species of juniper (Juniperus spp.). Between the trees the ground is sparsely covered by grama, others grasses, herbs, and various shrubs, such as big sagebrush (Artemisia tridentata) and alderleaf cercocarpus (Cercocarpus montanus).
The mountain zone extends over considerable areas on the high plateaus and mountains, but is actually much smaller than the pinyon-juniper zone. The vegetation varies considerably, from ponderosa pine in the south to lodgepole pine and aspen further north. Northern Arizona contains four distinct Douglas-fir habitat types (Alexander 1984). The lowest zone has arid grasslands but with many bare areas, as well as xeric shrubs and sagebrush. Several kinds of cacti and yucca are common at low elevations in the south.
Monoclines–local steepening in otherwise uniform, gently dipping strata–are the region’s single most distinctive structural feature. The Plateau also has igneous laccoliths, flat-bottomed igneous intrusive bodies that dome up over the sedimentary rocks, such as the Henry, La Sal, Navajo, Abajo, Ute, and Carrizo Mountains of southeastern Utah and northern Arizona (Morris 1994). The Plateau is bounded on the east by the southern Rocky Mountains, on the north by the central Rocky Mountains, and on the south and west by the Basin and Range Province.
Elevations in the Plateau are generally over 1525 m (5,000 ft), and in some areas are as high as 3960 m (13,000 ft). The climate is thus characterized by cold winters, and summers with hot days and cool nights. Average annual precipitation is about 510 mm, but some parts of the region receive less than 260 mm.
The Colorado Plateau is the only area in the United States and Canada where large mountain rivers run through exposed sandstone. That unique juxtaposition created the Grand Canyon, an internationally important ecotourism site, and other spectacular canyons in the region.
The Colorado River fish fauna display distinctive adaptive radiations. The humpback chub (Gila cypha), for example, is a highly specialized minnow that lives in the upper Colorado. It adapted to the water’s fast current and its extremes of temperature and volume. Dams and water diversion, however, have created a series of placid, still-water lakes and side streams, and the humpback chub may not be able to adapt to these altered conditions. The species, along with other native Colorado River fishes including the bonytail (Gila elegans), squawfish (Ptychocheilus lucius), and perhaps the flannelmouth sucker (Catostomus latipinnis), may not survive to the end of this century (Sigler and Sigler 1994).
This ecoregion is also rich in certain species of insects. The portion of the Colorado Plateau in the state of Colorado harbors 61 of the 131 species of grasshopper found in the state. The Plateau is also rich in ant species and supports several endemic leafhopper species (Nelson 1994).
Habitat Loss and Degradation
Approximately 15 percent of the Colorado Plateau remains as intact habitat. While little of the remaining 85 percent has been heavily altered by human activity, all show some signs of stress. Riparian areas and areas with mineral resources have been the hardest hit. The main reason for habitat loss in the region is grazing, and there is widespread grazing damage in the ecoregion. Other important causes of habitat loss include mining for coal and uranium, agriculture, invasion of exotics following heavy grazing, oil and gas exploration, dams, and urbanization, particularly around Albuquerque and Santa Fe, New Mexico.
Habitat loss is concentrated along Interstate 40 in the Four Corners region, along the Colorado River, and in the coal mining region in the northwest corner of the ecoregion.
Remaining Blocks of Intact Habitat
Several relatively large blocks of more or less intact habitat remain. Important blocks (mostly concentrated along the Colorado River) include:
•Grand Canyon National Park - northwestern Arizona
•Canyonlands National Park - eastern Utah
•Escalante-Capitol Reef-Kaiparorwits Plateau - south central Utah
•San Raphael Swell
•Navajo Mountain - southern Colorado
•Arches National Park - eastern Utah
•Cebolleta Mesa complex
•Sevilleta National Wildlife Refuge
Degree of Fragmentation
The southern and eastern parts of the Colorado Plateau have been fragmented by urbanization, mining, and agriculture. The Colorado River and Upper Rio Grande riparian corridors are also highly fragmented.
Degree of Protection
This ecoregion has numerous large protected areas, and is representative of most habitat types. Xeric shrubland is not well protected, but this habitat appears to be doing well outside of the reserves. The most important protected areas in this ecoregion include:
•Grand Canyon National Park
•Canyonlands National Park
•Arches National Park
•Dinosaur National Monument - western Colorado and eastern Utah
•Mesa Verde National Park - southwestern Colorado
•Sevilleta National Wildlife Refuge
•Capital Reef National Park
•Rio Grande NWSR
•Petrified Forest National Park - eastern Arizona
Types and Severity of Threats
While conversion of natural habitat to other uses poses a problem for only a small portion of the Colorado Plateau, urban and suburban development, strip-mining, and other activities threaten some of the most sensitive habitats in the region. Development is a particular problem near Albuquerque, Santa Fe, and Farmington, New Mexico. Strip-mining and the construction of a power plant threatens the Kaiparowits Plateau. The Animas-La Plata project, were it constructed, would destroy the river system and create agricultural land. Air pollution from uranium and coal mining poses the greatest degradation threat to the ecoregion, along with off-road vehicles, over-grazing, and excessive impacts of recreation around Moab. The greatest threat to wildlife on the Colorado Plateau is the destruction of native fish by dam-building and other forms of development.
Suite of Priority Activities to Enhance Biodiversity Conservation
•Repeal RS 2477. This federal law allow counties to establish rights of way across old cattle trails and horse trails on federal lands. Counties have made thousands of claims to rights-of-way within the Colorado Plateau. By exercising these rights, counties fragment public lands and thus disqualify them for wilderness designation, often leading to development.
•Control the impact of livestock grazing. Livestock grazing has serious impacts on riparian areas, which are the arteries of the plateau.
•Control exotics. Tamarisk, cheat grass, and other exotics threaten native plants and animals. This will require management plus research into the most cost-effective control methods.
•Protect Colorado River endangered fishes: Change reservoir operations to benefit fishes. For example, manage flows so as to mimic the natural hydrograph (floods), and release water from the top rather than the cold bottom of Glen Canyon reservoir (certain fishes need this warm water).
•Inventory and monitor biodiversity. Little is known about biodiversity in this region. In particular, there is a need to determine if/why amphibians are declining
•Protect neotropical migratory birds. We need to protect their nesting habitat in this region, but we also need to know what is causing their population decline -- is the problem on their wintering grounds, on their migration routes, or on their wintering range?
•Protect Threatened and Endangered Species. The Colorado Plateau has some localized threatened and endangered species. The Mexican spotted owl (Strix occidentalis lucida) tends to occur in areas where people like to recreate, leading to conflicts.
•Repeal the salvage logging rider. A number of southern Utah forests have been targeted for logging under the provisions of the salvage rider.
Recommendations are based in part on conversations with Ken Rait of the Southern Utah Wilderness Alliance (801- 486-3161) and Michael Britten of the National Park Service, Colorado Plateau Cluster Unit (303-987-6705).
•Grand Canyon Trust
•The Nature Conservancy of Arizona
•The Nature Conservancy of Colorado
•The Nature Conservancy of New Mexico
•The Nature Conservancy
•The Nature Conservancy of Utah
•The Nature Conservancy - Western Region
•Navaho Nation Natural Heritage Program
•Southern Utah Wilderness Alliance
•Utah Wilderness Coalition
Relationship to other classification schemes
Bailey’s Colorado Plateau Semi-Desert Province begins further to the south than this ecoregion. Much of what we classify as Colorado Plateau shrublands Bailey includes in the Intermountain Semi-desert and Desert Province. That province, however, extends far to the west and covers most of the Great Basin. Including northeastern Utah and northwestern Colorado but not western Utah in the Colorado Shrub Steppe provides a more consistent and manageable ecoregion. This ecoregion corresponds more closely to two of Omernik’s ecoregions, the Colorado Plateaus and the Arizona/New Mexico Plateaus.
Prepared by: S Primm.