Colorado Plateau Ecoregion
Description & Physiography
Spanning approximately 48.5 million acres (19.6 million ha, or 76,000 mi2) in the four-corners region of the southwestern United States, the Colorado Plateau includes landscapes that remain among the most remote in the lower 48 United States. It has long attracted seekers of wild beauty, and includes some of the most spectacular scenery in the world. Extensive plains, sheer-walled canyons, buttes, mesas and badlands dominate sedimentary surface deposits throughout the ecoregion.
The Colorado Plateau falls primarily within the Colorado River watershed, which defines much of its mid-elevation character between the Rocky Mountains (eastward) and the Mojave and Sonoran Deserts (southwestward). To the north and northwest, a “grand staircase” of cliffs ascends into the adjacent Utah High Plateaus. To the east, rapid elevation gain extends into the Southern Rocky Mountains. To the south, the Arizona-New Mexico Mountains form much of the higher-elevation perimeter. These surrounding mountainous ecoregions share similar ecological systems and species, including wide-ranging carnivores (e.g., wolf, black bear, mountain lion) and ungulates (e.g. elk, pronghorn, mule deer). To the west, below the Grand Wash Cliffs, lies the Mojave Desert.
The Colorado Plateau is commonly referred to as cold desert. However, a complex set of factors, including temperature, precipitation, and their seasonality, all help to define the ecoregion climate. Average temperatures vary according to the season and particular elevation, with all of the ecoregion receiving at least some snowfall. As with other portions of the intermountain west, continental-scale climate is driven by the rainshadow effect from the Sierra Nevada to the west and the main Rocky Mountain cordillera to the east.
Plants & Animals
The Colorado Plateau supports numerous species that are found nowhere else in the world. By far the richest taxonomic group of such species is the plants, with over 300 endemics known in the ecoregion. Several examples of endemic plants include the Jones cycladenia (Cycladenia humilis var. jonesii), Shultz stickleaf (Mentzelia shultziorum), Jane’s globemallow (Sphaeralcea janeae), Kachina daisy (Erigeron kachinensis), and Welsh’s milkweed (Asclepias welshii). In addition, the Colorado Plateau is known for its high species richness in several plant genera such as Penstemon, Eriogonum, and Astragalus.
Examples of endemic vertebrates include the Kaibab squirrel (Sciurus aberti kaibabensis); banner-tailed kangaroo rat, Bailey’s race (Dipodomys spectabilis baileyi); desert night lizard, Utah race (Xantusia vigilis utahensis); and Gunnison sage grouse (Centrocercus sp.). Though the casual observer may view its landscapes as largely intact, the Colorado Plateau has experienced a number of species losses. More well-known are several prominent vertebrate species that have been extirpated from the Colorado Plateau and remain in various stages of imperilment throughout their ranges. Such species include the grizzly bear (Ursus arctos), gray wolf (Canis lupus), black-footed ferret (Mustela nigripes), lynx (Lynx lynx), wolverine (Gulo gulo), and wild populations of bison (Bison bison) and river otter (Lontra canadensis).
Humans & History
Paleoecology, or the study of past environments, has been the focus of much research throughout the Colorado Plateau, providing important insight into ecosystem change. Using fossilized plant materials from the preserved middens of packrats and other sources, researchers have developed much greater understanding of major vegetation patterns over recent millennia. For example, during the end of the last glacial period, generally warmer temperatures on the Colorado Plateau forced many species of the mixed conifer forests upslope, leaving scattered relicts of Douglas-fir, white fir, and modern-day montane riparian species in relatively cool, moist canyon sites where microclimates remain favorable. This is the period generally recognized to include the extinction of many large carnivores and ungulates, such as the Columbian mammoth (Mammuthus columbi) and Shasta ground sloth (Nothrotheriops shastensis). The roles of humans in these extinctions, and their relative impact on ecosystem dynamics, remain areas of much research.
The earliest known inhabitants were characterized by an emphasis on big game hunting, supplemented by the gathering of wild plant foods. Between 10,000 and 8,000 years ago, shifts in temperature and precipitation regimes led to alterations in subsistence patterns over the following 6,000 years. During this time, the Pueblo people constructed impressive towns such as those in Chaco Canyon, Mesa Verde, and Tsegi Canyon. Archaeological studies indicate a short duration of many such settlements; the need to re-locate may have been due to depletion of wood resources, local population pressure, and a long period of drought.
The region was settled by people of European descent beginning in the 1850’s, primarily through colonization efforts by members of the Church of Jesus Christ of Latter Day Saints, who supported themselves mostly through agriculture, ranching, and some timber harvest from surrounding highlands. Grazing by non-native cattle and sheep reached massive levels toward the end of the 19th century, and remained uncontrolled at least into the 1930’s with the advent of the Taylor Grazing Act.
The 20th century brought striking and profound changes to the lands and waters of the Colorado Plateau. Water resources and hydrologic regimes have been “harnessed” to suit human purposes on scales from the tiny (irrigation diversions on many perennial streams) to the huge (Lake Powell). Changes in flow regime and introductions of non-native, predaceous fish species have caused steep declines in native fish populations in the region’s large warm rivers.
Exploration for and extraction of mineral resources has gone through several up and down cycles in the past 100 years. An upturn in energy exploration in the region occurred in the last decade. Most recently, and layered on top of all the “traditional” uses noted above, the region has seen an explosive proliferation of recreational activities. The zealous, global promotion of visitation to the region’s scenic wonders (including several National Parks) has brought a tidal wave of campers, hikers, climbers, mountain-bikers, and off-road vehicle enthusiasts to the Colorado Plateau. Aided by their technologically-advanced equipment and their ability to carry water, recreationists are now trampling many parts of the Colorado Plateau that escaped the abusive overgrazing of the early 20th century. The largely-intact, “undeveloped” appearance of much of the region (i.e. absence of towns, farms, parking lots, strip malls, golf courses, etc.) belies the fact that profound alterations continue to impact its plant communities, soils and waters.