RANGELANDS 15(5), October 1993 213 The Rangelands of Colorado John E. Mitchell To understand the rangelands of Utah border also receives very little Physlographic Regions Colorado,one should first look at its precipitation. Note: It is not com- Physiographers have dividedColo- physiography. Colorado can right- monly known that the stretch of the the be called the"zenith" of the Uni- ColoradoRiver between Grand Lake rado into three major provinces: fully and ted States; on is the and its confluence with Green Great Plains, Rocky Mountains, average, it high- the From a est state in elevation with morethan River in eastern Utah was called the Colorado Plateaus (Fig. 1). of time, these 50 peaks exceeding 14,000 ft. Moun- GrandRiver by early pioneers (Stan- perspective geological Iandforms are young.The pres- tain passes crossingthe Continental ton 1965).] quite Divide in ent Rocky Mountains were uplifted Colorado frequently are Like other western states, Colo- The Great above ft. The lowest in radois The only 60 million years ago. 11,000 point predominantly rangeland. ofalluvial mater- the state, the Arkansas River 1979 Assessment of the U.S. Forest Plainsare composed along ial that eroded from these where it enters is and mandated uplifting Kansas, only slightly Rangeland Situation, and were over below 3,400 ft., while about 95% of the Renewable Resources Plan- mountains deposited by thick mantles of ancient worn Colorado'sland area is morethan "a Act of estimated that 47.5 gravels ning 1974, from ancestral Rockiesformed mile The headwaters of four million ac., or 72°Jo ofthe state's lands away highl" the Paleozoic Era major rivers can be found in the are About 55%of this during (Chronic grazed. acreage and Chronic 1972). The Colorado Coloradomountains—the Colorado, is in private ownership. Of the 22 mil- North and South lion acres under Federal a Plateau is dominatedby sedimentary Platte, Arkansas, control, shales and sandstones laid down and Rio Grande. The watersheds of little morethan one-third is managed these rivers and during the Cretaceous Period, from their tributaries by the Bureau of Land Management and account for 20% of the area of the 48 while 63% is on National Forests. 70 to 135 million years ago, the ColoradoRiver and its conterminousstates. underthe control of the carved by Rangelands tributariessince that time. Although Colorado is high in ele- Defense Department, such as the vation, it tends to be low in Pinon Maneuver Site, The rangelands of Colorado are relatively Army's Canyon linked toits precipitation except for a few comprise mostof the remaining Fed- inexorably physical geog- high- and the differences elevationpeaks along the Continen- eral land. raphy underlying tal Divide. The Sierra Madre Range near Steamboat Springs is the only mountainous area with annual pre- cipitation exceeding 50 in. In general, precipitationin the mountains ranges between 20 and 50 in/year, distrib- uted fairly even throughout all sea- sons. On the eastern plains, precipita- tion is sparse, falling mostly during the spring and summermonths from convective thunderstorms. Alongthe Arkansas Rivervalley east of Pueblo, annual rainfall is less than 12 in. It rangesfrom 12 to 16 in. throughout mostof the highplains, butapproach- es 20 in. in the sandhills region of northeastern Colorado. The state's driest climate,with an annual precip- itation of less than 7 in., is found in the San Luis Valley. The Grand Val- ley between GrandJunction and the Fig. 1. Three ,na/or physiographic provinces in Colorado (adapted from Chronic and Theauthor is arange scientist, Rocky Mountain Chronic 1972). Forest and Range Experiment Station, 3825 E. Mulberry,Fort Collins, Cob. 80524. He wishesto thank Prof. Clinton Wasserfor providing back- ground informationfor this paper. 214 RANGELANDS 15(5), October 1993 in climatearid soils.The threeprom- inent provinces and their attendant ecosystems contain a rich diversity ofvegetation, wildlife, and otherfauna. Vegetation of the Plains The grasslands of the Great Plains are classified into three well-known divisions: the tall-grass prairie, the mid-grass prairie, andthe short-grass steppe. Two of the three have fun- damentally changedsince European settlement. In the tall-grass prairie, nativespecies have been largely re- placed by the introduced tall grass, corn. At the same time, native mid- grass prairiespecies have been exten- sively supplantedby a groupof agro- nomic mid-grasses, wheat. Only the Fig. 3. The shortgrasssteppe was considereda wastelandby travellers in the early 19th short-grass plains remains largely century,suitable only for Indiansand buffalo. Todayit is the principalran geland vegeta- under native sod. tion zone in Colorado. James A. Michener, in his classic vation of the Soil Bank. novel, Centennial, adroitly captured had been abandoned and gone into provisions a period in history when man attemp- default. Theselands were to become Whenthe Soil Bankpayments ended, ted to supplant the native short- the Pawnee and Comanche National nearly all of the acreage involved reverted to because grasseswith wheat and milo.Farmers, Grasslands, now managed by the grain production predominately were en- U.S. Forest Service. of economicconsiderations. immigrants, This is ticed to Colorado during the early During World War II, much of the process essentially repeat- 20th century by the railroads and short-grass plains wereagain plowed ing itself as a result of the Conserva- other interest with the to small This time, how- tion Reserve Program (CRP) of the groups prom- grow grains. In ise that wheatcould be grown on 12 ever, the governmentdid not buy the 1985Food Security Act. Colorado, in. of rain The Dust Bowl landwhen times laterbecame almost 2 million ac. of croplandhave per year. tough. into CAP. These years ofthe 1930's burstthat balloon, Rather, in the 1960's it contracted been placed the and the Federal with farmers to seed their lands comprise a major, if tempor- government pur- eroding incrementto chased large amounts of land that lands back into grass under conser- ary, Colorado'srange- lands(Fig. 2). Oneof the goalsof the Society for Range Management is to minimize the amount of CRP land with highly erodiblesoils that will be plowed out for row crop production at the end of the program. The tall-grass prairie is dominated by the genera Andropogon, Schiz- achyrium, Sorghastrum,and Panicum. Only remnants of this prairie are found in Colorado. However, it may have occupied much larger areas within theColorado Piedmont, agen- tle valley running north-south between the Rockiesand high plains, prior to European settlement. This depressed area tends to concentratesoil water, thereby providing suitable conditions for tall-grass communities. Numer- ous reservoirs and wetlands may be found within the Colorado Piedmont today, nearlyall whichis underunder Fig. 2. Extent anddistribution oflands in Colorado enrolledin the ConservationReserve irrigated agriculture or devoted to Program of the 1985Food Security Act. urbanuse. Anexcellent example of a RANGELANDS 15(5), October 1993 215 Ag. 4. Subalpinemeadow in north central Colorado. These meadowsprovide muchof the availablelivestock forage in the lodgepolepine and spruce-fir zones and are also valuableto elk. true tall-grass relict area is located steppe, dominated by blue grama 1961). Today, rivers traversing the withinthe City of Boulder Open Space. and buffalo grass (Fig.3). Bluegrama Great Plains flow year-round, provid- On deep, sandysoils coveringthe was designated the state grass of ing a differentwater regimefor ripar- uplands ofextreme eastern Colorado, Colorado in 1987. Other major spe- ian ecosystems. Beforewater devel- a tall-grass prairie, represented by cies includewestern wheatgrass, sand opment, trees were widely scattered grasses such as sand bluestem, dropseed, prickly-pear cactus, and along the South Platte River (Con- switchgrass, prairie sandreed and scarletglobemallow. The most com- klin 1928), but, by 1900, plains cot- side-oats grama, occurs on nearly mon shrub is four-wing saltbush. tonwoods had become increasingly 1.7 million ac. Annual precipitationis Prior to the mid-l9th Century, the established (Crouch 1961). Willows 12-16 in., 75% of which is received short-grass steppe was home to are found with cottonwood in ripar- between May andOctober. This prair- countless bison, antelope, prairie ian zones that are not heavily grazed ie provides excellent habitatfor small dogs and otherherbivores. The vege- during the summergrowing season mammals, upland game birds and tation present has, consequently, (Sedgwickand Knopf 1991). other animals. The dominantshrub, evolved under unmitigatedgrazing, Understoryspecies in plains ripar- sand sagebrush, also gives good cov- and is highly resistant to grazing Ian areas include prairie cordgrass, er and protection to wildlife. Endan- pressureby domestic herbivores(Klip- panicum, common reed, sedges,Can- gered species in this region include pIe and Costello 1960). Short-grass adawildrye,woods rose, goldencur- the American peregrine falcon. In communities also providegood pro- rant, and snowberry.A profusion of higher rainfall zones much of the tection from wind erosion. othergrasses, forbs and shrubsmay deepsand prairie is plantedto wheat Typical riparian zones in the east- also beencountered inthese riparian and milo. ern plains occupy flood plains and zones. Thetrue mid-grass prairie, as repre- adjacentbottomlands along braided Wildlifeare numerous on theshort- sented by different species