20 – Colorado Plateaus (6 – level 4 ecoregions)

“Ecoregion 20 is an uplifted, eroded, and deeply dissected tableland. Its benches, mesas, buttes, salt valleys, cliffs, and canyons are formed in and underlain by thick layers of sedimentary rock. Precipitous side-walls mark abrupt changes in local relief, often of 1000 to 2000 feet or more. The region contains a greater extent of pinyon-juniper and Gambel oak woodlands than the Wyoming Basin (18) to the north. There are also large low lying areas containing saltbrush-greasewood (typical of hotter, drier areas), which are generally not found in the higher Arizona/New Mexico Plateau (22) to the south where grasslands were typically more common. Summer moisture from thunderstorms supports warm season grasses not found in the Central Basin and Range (13) to the west. Many endemic plants occur and species diversity is greater than in Ecoregion 13. Several national parks are located in this ecoregion and attract many visitors to view their arches, spires, and canyons. (USGS, 2006; US EPA, 2013)”

20a – Moniticello-Cortez uplands and sagebrush valleys

• Topography - Parts of the gently sloping Monticello-Cortez Uplands and Sagebrush Valleys ecoregion are covered by eolian material.

• Land Use - Shallow or stony soils occur along the rims of benches and minor escarpments and support pinyon-juniper woodland.

• Soils - These soils now sustain dryland farming, with more irrigated agriculture to the east. Crops include pinto beans, Anasazi beans, winter wheat, oats, and alfalfa.

• Vegetation - Deep, silty soils are typical and retain enough available moisture to naturally support Wyoming big sagebrush and associated grasses.

• Other –

Sites to Visit - Cortez, Dove Creek, Pleasant View
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20b – Shale deserts and sedimentary basins

• Topography - The arid Shale Deserts and Sedimentary Basins ecoregion consists of nearly level basins and valleys, benches, low rounded hills, and badlands. Rock outcrops occur.

• Land Use - Land use includes rangeland, pastureland, and dryland and irrigated cropland, with winter wheat, small grains, forage crops, and pinto beans as major crops. The valleys of the Gunnison and Colorado rivers have areas favorable for growing apples, peaches, pears, and apricots. Shrublands provide important winter habitat for wildlife.

• Soils - Soils are shallow and types range from clayey to silty. Soils that formed primarily on Mancos shale are found in the areas northwest of Rangley, east of Meeker, in the Grand Valley, in Dry Creek Basin and Disappointment Valley southwest of the Uncompahgre Plateau, and in southwest Colorado near the Mancos River. The Mancos shale basins have the potential for high selenium levels, a particular problem in areas with irrigated agriculture. Soils formed from sandstone, limestone, shale, and gypsum are found in Paradox and Big Gypsum valleys southwest of the Uncompahgre Plateau. Soils formed from claystone, shale, sandstone, and mudstone are found west of Meeker, and in the Colorado River valley near Rifle.

• Vegetation - It is sparsely vegetated with mat saltbush, bud sagebrush, galleta grass, and desert trumpet. Floodplains have alkaline soils that support greasewood, alkali sacaton, seepweed, and shadscale. Scattered, gravel-capped benches occur and protrude from the present denudational surface because they are more resistant to erosion than the surrounding shales.

• Other –

Sites to Visit - James Robb Colorado River State Park, Sweitzer Lake State Park
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20c – Semiarid benchlands and canyonlands

• Topography - Broad, grass-, shrub-, and woodland-covered benches and mesas characterize the Semiarid Benchlands and Canyonlands ecoregion. Areas of high relief alternate with areas of low relief. Low escarpments separate remnant mesa tops and narrow canyons from surrounding benches.

• Land Use - Livestock grazing is a dominant land use, although stock carrying capacity is limited. On floodplains and terraces, some irrigated cropland occurs, primarily hay and grain for livestock. Oil and natural gas wells, oil shale extraction, and coal mining are also present in the region.

• Soils - Bedrock exposures (e.g., slickrock and fins) are common along rims, escarpments, and on steep dip slopes. Deep eolian soils are composed of fine sand.

• Vegetation - Deep eolian soils support warm season grasses, winterfat, Mormon tea, fourwing saltbush, and sagebrush. Two-needle pinyon and Utah juniper occur on shallow, stony soils. Scattered areas of Gambel oak occur at higher elevations. Overall, the vegetation is not as sparse as in drier areas such as Ecoregions 20b and 20d.

• Other - Average annual precipitation in the Colorado portion of the region varies from 10 to 18 inches in lower areas; on the highest sites, such as Mesa Verde, 20 to 25 inches can occur. Fire suppression and erosion have allowed this woodland to expand beyond its original range.

Sites to Visit - Black Canyon of the Gunnison National Park, Blackridge Canyons Wilderness Area, Canyons Conservation Area, Canyons of the Ancients, Crawford Lake State Park, Dan Nobel State Wildlife Area, Dinosaur National Monument, Dominguez Canyon Wildlife Area, Dominguez Escalante National Conservation Area, Escalante State Wildlife Area, Gunnison Gorge Wildlife Conservation Area, Mesa Verde National Park, Ridgeway Reservoir State Park, Rio Blanco Lake State Wildlife Area, Uncompahgre National Forest
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20d – Arid canyonlands

• Topography - Occurring primarily in Utah, the Arid Canyonlands ecoregion includes the inner gorge of the Colorado River and its major tributaries. Much of this ecoregion is bounded by nearly vertical canyon walls that separate it from the adjacent, higher benchlands of Ecoregion20c.

• Land Use - Land use is mostly livestock grazing and recreation.

• Soils - Soils are shallower and have a drier moisture regime than those of Ecoregions 20a and 20c. Exposed bedrock is common.

• Vegetation - Blackbrush, shadscale, and drought-tolerant grasses including galleta grass and Indian ricegrass occur. Blackbrush is more common here than in Ecoregion 20c, where pinyon-juniper woodland and sagebrush dominate.

• Other - Annual precipitation is lowest in the deepest canyons, mostly less than 10 inches.

Sites to Visit - Mancos River, Route 160
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20e – Escarpments

• Topography - The Escarpments ecoregion is characterized by extensive, deeply-dissected, cliff-bench complexes that ascend dramatically from Ecoregions 20b or 20c to the forested mountain rim. Local relief can be as great as 3000 feet, and the region is prone to landslides. Ecoregion 20e includes major scarp slopes of the Book Cliffs and Roan Cliffs.

• Land Use - This rugged, remote, and varied landscape provides habitat for wildlife.

• Soils -

• Vegetation - Natural vegetation varies according to aspect and moisture availability, ranging from Douglas-fir forest on steep, north-facing slopes at higher elevations to desert and semidesert grassland or shrubland on lower, drier sites. Pinyon-juniper woodland often dominates escarpments and benches that are covered by shallow soils.

• Other –

Sites to Visit - Book Cliffs, Douglas Pass, Roan Cliffs
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20f – Uinta basin floor

• Topography - Occurring primarily in Utah, the Uinta Basin Floor ecoregion lies in a large synclinal basin enclosed by the Uinta Mountains and Tavaputs Plateau.

• Land Use - Ecoregion 20f is distinguished from other arid basins by the abundant stream runoff it receives from the mountains in Utah. Streams are often diverted for irrigation. Alfalfa, small grain, and corn are grown for silage on arable, gently-sloping terraces and valley floors. Stonier soils are irrigated for pasture where and when water is available. Non-irrigated areas are used for livestock grazing.

• Soils -

• Vegetation - Saltbush-greasewood is the natural vegetation type.

• Other - Precipitation is low and soils are arid. Winters are constantly cold and often foggy due to frigid, dense air draining from the adjacent uplands and resultant air temperature inversions.

Sites to Visit - Dinosaur, Route 64
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