Snowpack Rescue

A series of Pacific storms will pummel the Cascades and Sierra Nevada for the next few days and  produce flooding along the West Coast.  Over the next week, the snow is forecast to spread throughout the Intermountain region, including the mountains of Idaho, the Great Basin, the Wasatch Front of Utah and the Rocky Mountain corridor.

Snowfall has been far below normal throughout most of the American West this winter, endangering its varied ecosystems and the water supply of its cities.  These storms are expected to significantly boost the mountain snowpack across that region, a welcome development as we approach March.

Of course, higher elevations of the West can generally expect more snow through the spring and peak snowmelt does not generally begin before mid-late May.  Hopefully, this vital recovery will continue until then. 

Desert Southwest Flooding

Copious moisture from tropical systems off the coast of northwest Mexico has spread northeastward into the Desert Southwest.  Flooding has occurred, and will continue to develop, across Arizona, southern Nevada, Utah, New Mexico and Colorado.  Some of that tropical moisture is expected to reach Metro Denver this morning.

Up to five inches of rain is expected across southern Arizona and daily precipitation records have occurred from that region to Grand Junction, Colorado (including a record 0.92 inch in Las Vegas).  What may seem to be rather meager totals for those of us who live in other areas of the country are not readily absorbed in desert terrain, leading to rapid runoff and flash flooding.

Fueled in part by a deep atmospheric trough over the Desert Southwest, the moisture flow will likely continue for another 48 hours and normally dry creeks and washes may become raging torrents.  Hopefully, those who live along those drainage channels will heed Weather Service warnings. 

Land of Laccoliths

Laccoliths are isolated rock formations, mountains or mountain ranges that result from the injection of magma into overlying layers of sedimentary rock.  Cooling into igneous rock, the laccolith is uncovered as the crust in which it lies is uplifted by tectonic forces and the softer sediments encasing it erode away.

Some of the most famous laccoliths in the United States are found in the Four Corners region of the Colorado Plateau.  The La Sal Range, just southeast of Moab, the Abajo Mountains, west of Monticello, the Henry Mountains, west of Canyonlands National Park and Navajo Peak, ENE of Page, Arizona (just north of the Utah-Arizona border), are prominent features of the landscape in southeastern Utah.  In extreme southwestern Colorado, Sleeping Ute Mountain (southwest of Cortez; photo below) and the La Plata Range (northwest of Durango) are well known laccoliths.

The intrusions in Utah occurred during the Oligocene and Miocene Periods (20-30 million years ago) while those in southwest Colorado were emplaced during the Laramide Orogeny (the first uplift of the Rocky Mountain Chain), some 65-70 MYA.  Of course, over the coming eons, these scenic mountains will also succumb to the relentless forces of wind, water and ice.  Better go see them before it's too late! 

From Shiprock to Ridgway

Early this morning, I left Farmington, New Mexico and drove west through the San Juan Valley.  The silhouette of Shiprock loomed in the distance, backed by the uneven wall of the Chuska Mountains.  Once in the area, I had to drive to the south side of that famous volcanic landmark to get a photo unmarred by structures or power lines.

Completing that goal, I continued westward on US 64 to Teec Nos Pos, just inside Arizona, and then turned northeast of US 160, soon passing the Four Corners Monument, crowded with tourists.  Just beyond that human-designated geographic point, I crossed the San Juan River for the final time as it flowed northwestward into Utah.  The Abajo Mountains rose to the NNE (in Utah) and the more distant La Sals shimmered farther north; closer and more dominant was the massive bulk of Sleeping Ute Mountain, a laccolith within the Ute Reservation of extreme southwest Colorado.  Passing to the south and then to the east of that sacred mountain, I headed toward Cortez; Lone Cone, the westernmost peak of the San Juans beckoned from the north and the La Plata Mountains reappeared to the east.  From Cortez, I followed Route 145 northward and soon dropped into Dolores on the Upper Dolores River; the road then climbs northward through that river's scenic canyon, eventually reaching Lizard Head Pass (10,222 feet) and then descending to Telluride.

After a walk and some lunch in that scenic mountain town, I continued down Route 145 along the San Miguel River (a tributary of the Dolores) to Placerville and then turned east on Route 62, which crosses the Dallas Divide (8900 feet); this open ridge offers a spectacular view of The Needles, to the south, and of other San Juan Mountains to the southeast.  The road then drops to Ridgway, in the Uncompahgre River Valley; this town, in my opinion, occupies one of the most scenic locations in Colorado.  Having completed my loop of the Four Corners region, I headed to Gunnison to spend the night.

Into the San Juan Watershed

From Wolf Creek Pass (elevation 10,850 feet), in the southern San Juan Mountains, I left the Rio Grande watershed and entered that of the San Juan River, the Great River of the Navaho Nation.  Following a steep descent to Pagosa Springs, U.S. 160 fords the San Juan and begins to undulate westward through the foothills, crossing the Piedra, Los Pinos and Florida Rivers in sequence (all tributaries of the San Juan River); in doing so, the highway gradually moves away from the high wall of the Southern San Juans Mountains.

Nearing Durango, however, the road offers spectacular views of the La Plata Mountains, sculpted from a massive granite dome, which rise northwest of the city.  On the eastern side of Durango, I turned south on US 550, driving atop then within the canyon of the Animas River, among the largest tributaries of the San Juan.  With every mile toward the south, the landscape became noticeably drier, characterized by sage grasslands and mesas covered with piñon-juniper woodlands.

The Animas River joins the San Juan in Farmington, New Mexico, where I will spend the night, and the latter continues westward to Shiprock.  From there, it bows northwestward, passing near the Four Corners Monument before reaching Bluff, Utah; beyond that town, the San Juan snakes westward to join the Colorado River within Lake Powell.  Tomorrow, my wanderings will remain in the San Juan watershed until I cross a low divide between Cortez and Dolores, Colorado, thereby entering the watershed of the Dolores River.

Southwest to the Four Corners

Looking ahead to several days with no commitments, I have decided on a road trip to the Four Corners region, where the States of Colorado, New Mexico, Arizona and Utah meet.  Though I have been to that area in the past, there are several routes through its varied landscape that will give me a new perspective on the terrain and topography.  Now that we have entered the summer tourist season, I will skip Mesa Verde National Park which I had the pleasure to visit almost thirty years ago.

Geologically, the Four Corners is a land of volcanic features, superimposed on uplifted and eroded late Paleozoic and Mesozoic sediments.  Tributaries of the Colorado River drain the landscape; the San Juan rises from numerous rivers and creeks along the south flank of the the San Juan Mountains and then heads westward to join the Colorado in Lake Powell while the Dolores River drains the west flank of both the San Juans and the Uncompahgre Plateau as it flows NNW to merge with the Colorado northeast of Moab, Utah.  Other prominent natural features include Ship Rock (a remnant volcanic neck), Sleeping Ute Mountain, the  La Sal Range (east of Moab) and the Chuska Mountains (on the New Mexico-Arizona line).

Planning to leave Denver early tomorrow morning, I will follow U.S. 285 southwest, crossing Kenosha Pass to drop into South Park.  From there, the highway crosses Trout Creek Pass to enter the Upper Arkansas River Valley and then turns southward, climbing over Poncha Pass to reach the broad San Luis Valley.  Within that valley I will switch to U.S. 160, heading west and then southwest, climbing along the South Fork of the Rio Grande River to Wolf Creek Pass.  Beyond that pass, a long descent will take me through Pagosa Springs and into Durango, where I will likely spend the first night.  More details in coming posts.

See also: San Juan Volcanism

Through Riverless Terrain

Leaving Ely, Nevada, this morning, we headed east on US 50; our first stop was Great Basin National Park, in the Snake Range, just west of the Utah Border; details regarding the Park are provided in the linked post.  Today, a deep snow pack closed the Wheeler Peak road at Mather Overlook (just above 9000 feet) but we enjoyed broad views of the Park and adjacent landscape.  We then took a hike along South Baker Creek before setting out across the beautiful but arid lands of the Great Basin.

One of the highlights of that journey was the vast but dry bed of Sevier Lake; filled to the brim during the cool, wet climate of the Pleistocene, the lake is now a sink, fed by the fickle flow of several basin rivers that have been mostly dammed or diverted.  After crossing Interstate 15, we climbed along US 50 to merge with Interstate 70 and then crossed the massive hump of the Wasatch Plateau; beyond this high ridge the highway winds through some of the most scenic topography in North America (if not on the planet) where eroded beds of late Paleozoic and Mesozoic sedimentary rocks line the road.  After dropping through the Waterpocket Fold, we crossed the Green River, completing our loop through Utah, Nevada and California.

Looking down at that River, it occurred to me that this tributary of the Colorado was the first stream of any size that we had crossed since leaving Mono Lake; indeed, the West Fork of the Walker River, north of that lake was the last river that I had encountered.  Such is the nature of the Great Basin: two days of driving through magnificent but riverless terrain.

From Denver to Salt Lake

Beginning the first leg of our California road trip, we left Denver this morning, headed west on Interstate 70.  Climbing through the Front Range, we crossed the Continental Divide at the Eisenhower Tunnel and entered the vast watershed of the Colorado River.  After dipping through the Blue River Valley, we crossed Vail Pass and descended along Gore Creek and the Eagle River to the Colorado itself.

Following the Colorado, we snaked down Glenwood Canyon and, just west of Glenwood Springs, cut through the Grand Hogback, entering the Colorado Plateau, a landscape of mesas, buttes, plateaus and cliff-lined valleys.  Passing Battlement and Grand Mesas to our south and the Roan Plateau to our north, we then drove along the Book Cliffs (Cretaceous in age), that rise along the north side of the Interstate from Grand Junction to Green River, Utah.  Leaving the Colorado, we entered Utah where the La Sal Mountains, a massive laccolith near Moab, loomed to the SSW; after crossing the Green River, just east of the Waterpocket Fold, we turned north on US 6 toward Price, Utah, passing formations of Mancos Shale carved by the Price River and its tributaries.

Beyond Price, the highway climbs onto the Wasatch Plateau where, at Soldier Summit (7477 feet), we left the watershed of the Colorado River and entered the Great Basin, dropping from the Plateau and through the Wasatch Range to the urban corridor of Provo and Salt Lake City.  Tomorrow, we cross the Great Basin on Interstate 80, headed for Reno and Lake Tahoe.

Flaming Gorge

The Green River of the Western U.S. rises on the northwest flank of the Wind River Range in west-central Wyoming and flows southward through its broad basin of Tertiary and Cretaceous deposits.  Approaching the Utah border, it has sculpted Flaming Gorge, named by Major John Wesley Powell for bright red Triassic rocks that adorn southern portions of the chasm; the scenic gorge now lies within the Flaming Gorge National Recreation Area.

Having initially established its course in Tertiary sediments (from the Green River Lakes, regional volcanism and mountain erosion) the Green River cut through the eastern end of the Uinta Range as it rose from below during the Miocene-Pliocene Uplift.  Today, the northern two-thirds of the Gorge is carved in Eocene deposits while the southern third is lined by a progression of Mesozoic, Paleozoic and Precambrian rock (north to south); along its 91 mile course in the Gorge, the Green River (dammed since 1964) has cut through strata representing at least 700 million years of Earth's history.

As we found out today, the Utah portion of the Flaming Gorge NRA is especially scenic, with steep cliffs that rise 1700 feet above the lake; mountainous terrain surrounds the gorge and road signs introduce visitors to the varied rock strata.  To the north, in Wyoming, the lake shimmers amidst a vast sage grassland, broken by Tertiary domes, buttes and mesas that illustrate the erosive power of the Green River and its tributaries over the past 30 million years.

Journey to Flaming Gorge

Though my wife and I have traveled extensively throughout the Western U.S., a visit to Flaming Gorge, on the Wyoming-Utah border, has eluded us.  Over the next few days, we plan to remedy that deficiency.

This afternoon, we'll head west on Interstate 70, climbing to the Continental Divide, dipping through the Blue River Valley, winding across Vail Pass and eventually merging with the Colorado River to snake through Glenwood Canyon.

After a night in Glenwood Springs, we'll leave Interstate 70 at Rifle, angling northwest across the Roan Plateau of northwest Colorado and the Uinta Plateau of northeast Utah, both of which are topped by Eocene sediments of the Green River Formation (see Green River Lakes).  From Vernal, Utah, we'll head north to Flaming Gorge, sculpted by the Green River over the past 30 million years and flooded by Flaming Gorge Lake since 1964; more on the Gorge tomorrow.

Mountain Plovers

The only thing "mountain" about mountain plovers is that they summer and breed in the Mountain Time Zone.  Preferring short-grass prairie and other flatlands with sparse vegetation, they nest on the High Plains, from southernmost Canada to eastern New Mexico and West Texas; small populations have also been found in Utah.

Soon after arriving on the High Plains in spring, mountain plovers pair off and scoop out a number of shallow depressions, one of which is eventually used for the nest.  As with most "shorebirds," the young are active soon after hatching and hunt for insects with their parents.  Those hoping to encounter mountain plovers are advised to drive along graveled country roads of the High Plains, especially in the National Grassland areas; since they prefer sparse vegetation, these birds are often best found in and around prairie dog colonies.  Rather tame, they seldom fly off as your vehicle approaches, preferring to run away or flatten themselves against the stark terrain to avoid detection; among their natural enemies are prairie falcons, Swainson's hawks, swift fox, coyotes and rattlesnakes.  Challenged by loss of prairie habitat, mountain plovers have adapted to the presence of cattle (surrogates for the great bison herds) and are not officially listed as a threatened species by the U.S. Fish & Wildlife Service.

Come fall, mountain plovers head for wintering grounds in the valleys of California or in desert grasslands of southern Arizona, northern Mexico or West Texas; those that breed in southern regions of the High Plains may not migrate if insects and other terrestrial invertebrates remain available.  Since they tend to wander about during the autumn migration, it is then that they may turn up in unexpected habitat or distant from their usual range.

The Escalante River

The upper tributaries of the Escalante River rise on the Aquarius Plateau of southern Utah, a mesa capped by Tertiary volcanic rock and flanked by colorful outcrops of the Claron Formation (deposited during the Paleocene).  Tumbling to the desert floor, they flow southward, carving their way through Cretaceous strata that extend northeastward to the Waterpocket Fold and SSW to the Kaiparowits Plateau.

Nearing the main channel of the Escalante River, which begins at the town of Escalante, the tributaries and the primary stream begin to incise a layer cake of Jurassic sandstones, producing spectacular canyonlands.  Flowing eastward and then southeastward, the Escalante makes a tortuous, ninety-mile journey to the Colorado River, which it joins in Lake Powell; en route, the river and its tributaries cut down through Jurassic strata that span sixty million years of Earth's history.  Of course, in that arid landscape, that erosion is seasonal, occurring primarily during the spring snowmelt and the summer monsoon.

Protected within the eastern portion of the Grand Staircase Escalante National Monument (established in 1996) and a northern section of the Glen Canyon National Recreation Area, the remote Escalante was one of the last rivers in the U.S. to be completely mapped and remains one of the last free-flowing rivers in the American West.  Yet, conflicting regional interests, combined with the effects of water diversion, roadway construction and alien tree invasion (primarily Russian olive and tamarisk) have threatened the welfare of the Escalante; fortunately, the Escalante River Watershed Partnership, a concerted effort of local conservationists, State and Federal agencies and the Nature Conservancy, is working to restore the river's natural ecology while respecting the interests of those who rely on the Escalante for their recreation and livelihood.

Eolian Jurassic Sandstones

Three eolian (wind-deposited) Jurassic sandstones make a major contribution to the spectacular scenery of the Colorado Plateau.  These strata, initially emplaced as dune fields, have compacted into unique sedimentary rocks, cemented by heat and pressure over more than 150 million years.

The oldest of these is the Wingate Sandstone, deposited at the dawn of the Jurassic (about 200 million years ago); in most areas, it sits atop late Triassic redbeds of the Chinle formation.  The Wingate forms massive red cliffs with vertical striations, often giving it a curtain-like appearance.  Atop the Wingate, the Kayenta formation of horizontal siltstones, conglomerates and sandstone separates it from the second major eolian sandstone of the Jurassic, the Navaho Sandstone.  White to pale pink in color, the Navaho has horizontal striations and also forms prominent cliffs; however, it erodes into rounded domes, wavy ledges and curved slickrock formations, many of which are honeycombed and pock-marked by wind-driven sand.  The Carmel Formation, a thin layer of shale and limestone, sits atop the Navaho Sandstone, separating it from the Entrada Sandstone, a salmon-colored eolian sandstone that, like the Navaho, erodes into rounded outcrops.

Exposures of the Wingate and Navaho Sandstones are widespread across the Colorado Plateau; both form cliffs in Canyonlands National Park, in the Escalante River Canyon and on the Vermillion Cliffs, north of Kanab, Utah.  Wingate Sandstone forms the sheer walls of the Colorado National Monument while Navaho Sandstone forms the spectacular cliffs of Zion Canyon, the domes of Capitol Reef National Park and the towering rock walls along western portions of Lake Powell.  Entrada Sandstone also outcrops in Colorado National Monument but is most famous for its many arches and rock formations throughout Arches National Park.  Once desolate dune fields, these magnificent sandstones now invite exploration and their images grace calendars and coffee table books across the globe.

The Abajo Mountains

Anyone who has visited Arches or Canyonlands National Parks has surely noticed a cluster of mountains that rises to their south, towering above the dry, heavily dissected landscape of southeast Utah.  Just west of Monticello and north of Blanding, the Abajo Mountains, locally known as The Blues, are relatively gentle, rounded summits and were thus given a name that means "low" in Spanish.

The Abajos formed as intrusions of magma during the Miocene, some 25 million years ago.  As the Colorado Plateau rose during the Miocene-Pliocene Uplift, this laccolith, like the La Sals to its NNE and the Henry Mountains to its northwest, was uncovered as the softer sedimentary rocks in which it was encased eroded away.  Abajo Peak, the summit of this mountain cluster, tops out at 11,362 feet and is accessed by County Road 102 (reached via Forest Road 105, west of Monticello).  Topographically, the Abajos lie between the Colorado River canyon, to their northwest, and the canyon of the San Juan River, to the south; WSW of the Abajo Mountains, these two rivers merge within Lake Powell.

Remote and uncrowded, the Abajos are one of many "sky islands" across the Desert Southwest, offering a cool retreat in summer, spectacular aspen displays in autumn and a winter wonderland during the colder months of the year.  A ski resort once attracted visitors to the Abajo Mountains but has since closed; well prepared and adventurous hikers can thus explore this range in relative solitude, treated to a diverse population of mountain wildlife and to magnificent views across arid canyonlands to distant peaks and mesas.

Utah's Powder Keg

Famous for deep powder that attracts skiers from across the globe, the Wasatch Front of Utah is about to unleash its bounty on those who live along its base. Thanks to a persistent atmospheric trough that produced a chilly, wet spring, the snowpack is near record levels and has barely begun to melt, a process that generally peaks in May. When summer heat suddenly arrives, a torrent of meltwater will sweep through the steep canyons of that majestic range, inundating the towns and cities that lie in its path.

Unlike in other areas of the country, the rivers that drop into the Great Basin soon spread across the flat terrain, forming broad, shallow lakes that evaporate in the intense sun of the high desert. Of course, Salt Lake City and other urban centers now occupy that basin and, when reservoirs are unable to contain the flow, flooding results. In light of the deep snowpack and delayed melting cycle, such a scenario appears to be unavoidable.

The bounty of mountain snow is vital to the ecosystems of the Western U.S., sustaining forests and producing corridors of vegetation across the semiarid landscape that lies below; without it, humans could not have colonized the region. But nature is fickle, bringing drought one year and floods the next; we must understand the risks that come with her varied landscapes and learn to live with her changing moods.

The Virgin River Staircase

The North and East Forks of the Virgin River rise on the south face of the Markagunt Plateau, in southwest Utah, amidst colorful outcrops of the Claron Formation. From these early Tertiary sediments, the tributaries begin to flow back in time, entering Zion National Park through Cretaceous Dakota Sandstone before carving magnificent canyons of Jurassic Navajo Sandstone; the North Fork has produced the more famous Zion Canyon while the East Fork sculpted Parunaweep Canyon.

The Forks join west of Zion, where the Virgin River begins a journey across Triassic redbeds, interrupted by Quaternary basalt flows along the Hurricane Fault. Beyond St. George, the river dips into the northwest corner of Arizona, where it has carved the spectacular Virgin River Gorge through Permian limestone and older, metamorphosed Paleozoic strata. West of the Grand Wash Fault, which marks the west edge of the Colorado Plateau, the canyon widens and the river enters the stark landscape of the Mojave Desert. After flowing into Nevada, the Virgin River curves to the south and joins the Colorado River within Lake Mead.

Western rivers are appealing to the naturalist in many ways. Producing ribbons of vegetation through arid landscapes, they also reveal the complex geology that underlies and explains the rugged, surface topography. Though relatively short, the Virgin River of Utah-Arizona-Nevada has bestowed its gifts in spectacular fashion.

The Uinta Mountains

Looking at a map of North America, one notices that the major mountain ranges trend north to south; this reflects the compressive, subduction and, in the case of fault-block ranges, stretching forces that produced the uplifts, which have generally come from an east-west direction. Two exceptions are the Transverse Range of Southern California, created by northward compression along the San Andreas Fault, and the Uinta Mountains of northeast Utah.

The Uintas, the highest range in the State, formed during the Laramide Orogeny (70-60 million years ago), which lifted the Rocky Mountain chain. Pressure within the North American craton, presumably secondary to the Farallon Plate subduction along the west coast, crumpled ancient Precambrian bedrock up through the overlying Paleozoic and Mesozoic sediments. Parallel faults in northeastern Utah, running west to east, dictated the unusual orientation of the Uinta uplift; furthermore, subsequent shifts in the crust forced the initial anticline northward atop the edge of the Green River basin, tilting the block. This latter movement, along a thrust fault, explains why the crest of the Uinta Range is much closer to its steep northern slope than to its more gradual southern slope. The uplift of this massive range also produced deep basins to its north, south and east, which held the Green River Lakes of the Eocene, among the largest freshwater lake systems in the history of our planet.

During the Pleistocene, glaciers scoured the summits of the range and produced broad, U-shaped valleys on its flanks, especially along the south side of the Uintas; this glaciation also created massive domes and flat expanses of tundra, with numerous glacial lakes, atop the range. Drainage along the south side of the Uintas is via streams that flow southeastward across the Uinta Basin to join the Green River, a major tributary of the Colorado; most streams on the north side also drain to this River though the western third of the north flank feeds the Bear River, which flows to the Great Salt Lake.

Jurassic Parks

The Colorado Plateau of the Western U.S. harbors one of the most extensive exposures of Jurassic strata on our planet. Stretching from 200 to 135 million years ago, the Jurassic Period covered the heart of the Mesozoic Era, the Age of Dinosaurs.

A number of our National Parks and Monuments are famous for their Jurassic deposits and, by extension, their cargo of dinosaur fossils. Dinosaur National Monument, in northwest Colorado and northeast Utah, is a showcase for the Morrison Formation; deposited in a long, shallow basin, from Canada to New Mexico, this layer cake of mudstones, siltstones, coal and sandstone is famous for its late Jurassic fossils. A bit older, the Entrada Sandstone, deposited in the mid Jurassic, is highlighted at Arches National Park, in eastern Utah, where it has been sculpted into a spectacular array of fins, natural bridges and arch formations.

Perhaps most famous of the Jurassic sedimentary rocks is the Navajo Sandstone, deposited about 190 million years ago when a vast desert covered the region. Relatively soft and heavily jointed, this sandstone forms the upper cliffs of Canyonlands National Park, the scenic domes of Capitol Reef National Park and the towering walls of Glen Canyon, now drowned by Lake Powell. Separated from the Navajo Sandstone by the Kayenta Formation, the Wingate Sandstone yields the middle cliffs of Canyonlands and the majestic, sheer walls of Colorado National Monument; though officially dated from the onset of the Jurassic, some geologists argue that, based on its fossil contents, the Wingate was deposited near the end of the Triassic.

Claron Lake

When the Rocky Mountain chain began to rise, some 70 million years ago, the crust to its west was stretched, producing a mosaic of ridges and broad basins. Drainage into the basins created large inland lakes, including the Green River Lakes of the Utah-Colorado-Wyoming Tristate and Claron Lake of southwest Utah. All of these lakes gradually filled with sediments of the Paleocene and Eocene Periods (60-50 million years ago); the deposits in the Green River Lakes would eventually yield the famous oil-shales of the Roan Plateau while deposits in Claron Lake would become prized more for their natural beauty.

Compacting into layers of limestone, dolomite, siltstone and conglomerates and capped by volcanic tuff from the Oligocene Period (30 million years ago), the Claron Formation was lifted with the rest of the Colorado Plateau during the Miocene-Pliocene Uplift, some 25-10 million years ago. Erosion and faulting would eventually expose the Claron beds along the edge of regional plateaus; Cedar Breaks National Monument, a spectacular natural amphitheater on the west edge of the Markagunt Plateau and Bryce Canyon National Park, on the east edge of the Paunsaugunt Plateau, protect the most scenic exposures.

Rich in iron oxides and manganese oxides, the colorful limestones and dolomites have eroded into striking rock formations, known as hoodoos. These pinnacles, capped by more resistant rock layers have been split apart by stream erosion and freeze-thaw fracturing. Once lying beneath an ancient lake, they now gleam in the bright Utah sun and adorn calendars across the globe.

The Wasatch Plateau

Although its official extent seems to vary among geographers, the Wasatch Plateau is a high ridge of horizontal Tertiary and late Mesozoic sediments that angles NNE to SSW through central Utah. To the north, it merges with the southwest end of the High Uinta Range and, to the south, it drops to the high tablelands of northern Arizona. The Plateau itself represents the divide between the Great Basin, to its west, and the Colorado Plateau, to its east; the Bear, Provo, San Pitch and Sevier Rivers drain to the west while the Strawberry, Price, San Rafael and Muddy Creek Rivers, destined to join the Colorado, drain to the east. At the south end of the uplift, the Virgin River flows southwestward, joining the Colorado at Lake Mead.

South of I-70, I-15 parallels the west edge of the Plateau down to St. George, Utah, while, north of I-70, a series of mountain ranges (the Pavant, San Pitch, Wasatch Front and Bear River Range, south to north) rise west of the Plateau. These ranges, representing the easternmost fault-block mountains of the Basin and Range Province, are separated from the Wasatch Plateau by a chain of valleys, quilted with horse and sheep ranches; Heber City, in the Provo River Valley, Mt. Pleasant, in the San Pitch Valley and the towns of the Sevier River Valley lie along this corridor.

Though the highest elevations of the Wasatch Plateau top out below 11,500 feet, it forms an imposing and rugged wall, covered with a rich forest of spruce, fir and aspen. Known for its high concentration of mule deer, the Plateau is also home to elk, black bear, mountain lions, coyotes and a host of smaller mammals. Zion and Bryce Canyon National Parks, among the most scenic locations in the United States, occupy the southernmost portion of this magnificent ridge.