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THE TETON RANGE is one of the most magnificentmountain ranges on the North American Continent. Others are longer,wider, and higher, but few can rival the breathtaking alpine grandeur ofthe eastern front of the Tetons. Ridge after jagged ridge of naked rocksoar upward into the western sky, culminating in the towering cluster ofpeaks to which the early French voyageurs gave the name"les TroisTetons" (the three breasts). The range hangs like a great stone wavepoised to break across the valley at its base. To the south and east arelesser mountains, interesting and scenic but lacking the magic appeal ofthe Tetons.
This is a range of many moods and colors: stark andaustere in morning sun, but gold and purple and black in the softlylengthening shadows of afternoon; somber and foreboding when the peakswrap themselves in the tattered clouds of an approaching storm, buttranquil and ethereal blue and silver beneath a full moon.
These great peaks and much of the floor of the valleyto the east,Jackson Hole (ahole was the term used bypioneer explorers and mountain men to describe any open valley encircledby mountains), lie within Grand Teton National Park, protected andpreserved for the enjoyment of present and future generations. Each yearmore than 3 million visitors come to the park. Many pause briefly andpass on. Others stay to explore its trails, fish its streams, study theplants and wildlife that abound within its borders, or to savor thecolorful human history of this area.
Most visitors, whatever their interests andactivities, are probably first attracted to the park by its unsurpassedmountain scenery. The jagged panorama of the Tetons is the backdrop towhich they may turn again and again, asking questions, seeking answers.How did the mountains form? How long have they towered into the clouds,washed by rain, riven by frost, swept by wind and snow? What enormousforces brought them forth and raised them skyward? What stories arechronicled in their rocks, what epics chiseled in the craggy visage ofthis mountain land. scape? Why are the Tetons different from othermountains?
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How did the Tetons and Jackson Hole form? Theyare both tilted blocks of the earth's crust that behaved like twoadjoining giant trapdoors hinged so that they would swing in oppositedirections. The block on the west, which forms the Teton Range, washinged along the Idaho-Wyoming State line; the eastern edge was upliftedalong afault (a fracture along which displacement has occurred).This is why the highest peaks and steepest faces are near the eastmargin of the range. The hinge line of the eastern block, which formsJackson Hole, was in the highlands to the east. The western edge of theblock is downdropped along the fault at the base of the Teton Range. Asa consequence, the floor of Jackson Hole tilts westward toward theTetons (see cross section inside back cover).
When did the Tetons and Jackson Hole develop thespectacular scenery we see today? The Tetons are the youngest of allthe mountain ranges in the Rocky Mountain chain. Most other mountains inthe region are at least 50 million years old but the Tetons are lessthan 10 million and are still rising. Jackson Hole is of the same ageand is still sinking. The Teton landscape is the product of many earthprocesses, the most recent of which is cutting by water and ice. Withinthe last 15,000 years, ice sculpturing of peaks and canyons andimpounding of glacial lakes have added finishing touches to the scenicbeauty.
Why did the Tetons rise and Jackson Hole sink?For thousands of years men have wondered about the origin of mountainsand their speculations have filled many books. Two of the more populartheories are: (1) continental drift (such as South America moving awayfrom Africa), with the upper lighter layer of the earth's crust movingover the lower denser layer and wrinkling along belts of weakness; and(2) convection currents within the earth, caused by heat transfer,resulting in linear zones of wrinkling, uplift, and collapse.
These concepts were developed to explain the originof mountainous areas hundreds or thousands of miles long but they do notanswer directly the question of why the Tetons rose and Jackson Holesank. As is discussed in the chapter on mountains, it is probable thatsemifluid rock far below the surface of Jackson Hole flowed north intothe Yellowstone Volcanic Plateau-Absaroka Range volcanic area, perhapstaking the place of the enormous amount of ash and lava blown out ofvolcanoes during the last 50 million years. The origin of the line ofweakness that marks the Teton fault along the east face of the TetonRange may go back to some unknown inequality in the earth's compositionseveral billion years ago. Why it suddenly became active late in theearth's history is an unanswered question.
The ultimate source of heat and energy that causedthe mountains and basins to form probably is disintegration ofradioactive materials deep within the earth. The Tetons are aspectacular demonstration that the enormous energy necessary to createmountains is not declining, even though our planet is several billionyears old.
Visitors whose curiosity is whetted by this unusualand varied panorama are not satisfied with only a few questions andanswers. They sense that here for the asking is an extraordinarygeologic (geo—earth;logic—science) story. Witha little direction, many subtle features become evident features thatotherwise might escape notice. Here, for example, is a valley with anodd U-shape. There is a sheer face crisscrossed with light- anddark-colored rocks. On the valley floor is a tuft of pine trees thatseem to be confined to one particular kind of rock. On the rolling hillsis a layer of peculiar white soil—the only soil in which coyotedens are common. All these are geologically controlled phenomena. Inshort, with a bit of initial guidance, the viewer gains an ability toobserve and to understand so much that the panorama takes on new depth,vividness, and excitement. It changes from a flat, two-dimensionalpicture to a colorful multi-dimensional exhibit of the earth'shistory.
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The Tetons are a short, narrow, and high mountainrange, distinctive in the midst of the great chain of the RockyMountains, the backbone of western North America. Figure 1 shows how theTetons and their surroundings might appear if you viewed them from asatellite at an altitude of perhaps a hundred miles. The U. S.Geological Survey topographic map of Grand Teton National Park shows thenames of many features not indicated on figure 1 or on the geologic mapinside the back cover. The Teton Range is a rectangular mountain blockabout 40 miles long and 10-15 miles wide. It is flanked on the east andwest by flat-floored valleys. Jackson Hole is the eastern one and TetonBasin (called Pierre's Hole by the early trappers) is the western.
The Teton Range is not symmetrical. The highest peakslie near the eastern edge of the mountain block, rather than along itscenter, as is true in conventional mountains, and the western slopes arebroad and gentle in contrast to the precipitous eastern slopes. Thenorthern end of the range disappears under enormous lava flows that formthe Yellowstone Volcanic Plateau. Even from this altitude the outlinesof some of these flows can be seen.
On the south the Teton Range abuts almost at rightangles against a northwest-trending area of lower and less ruggedmountains (the Snake River, Wyoming, and Hoback Ranges). These mountainsappear altogether different from the Tetons. They consist of a series oflong parallel ridges cut or separated by valleys and canyons. Thispattern is characteristic of mountains composed of crumpled, steeplytilted rock layers—erosion wears away the softer layers, leavingthe harder ones standing as ridges.
On the east and northeast, Jackson Hole is bounded bythe Gros Ventre and Washakie Ranges, which are composed chiefly offolded hard and soft sedimentary rocks. In contrast, between thesemountains and the deepest part of Jackson Hole to the west, thick layersof soft nearly flat-lying sedimentary rocks have been sculptured bystreams and ice into randomly oriented knife-edge ridges and rollinghills separated by broad valleys. The hills east of the park are calledthe Mount Leidy Highlands and those northeast are the Pinyon PeakHighlands.
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If you descend from 100 miles to about 5 miles abovethe Teton region, the asymmetry of the range, the extra ordinary varietyof landscapes, and the vivid colors of rocks become more pronounced.
Figure 2 shows a panorama of the Teton Range andJackson Hole from a vantage point over the Pinyon Peak Highlands. Therough steep slopes and jagged ridges along the east front of the rangecontrast with smoother slopes and more rounded ridges on the westernside. Nestled at the foot of the mountains and extending out onto thefloor of Jackson Hole are tree-rimmed sparkling lakes of many sizes andshapes. Still others lie in steep-sided rocky amphitheaters near themountain crests.
One of the most colorful flight routes into JacksonHole is from the east, along the north flank of the Gros VentreMountains. For 40 miles this mountain range is bounded by broad parallelstripes of bright-red, pink, purple, gray, and brown rocks. Some cropoutas cliffs or ridges, and others arebadlands (bare unvegetatedhills and valleys with steep slopes and abundant dry stream channels).In places the soft beds have broken loose and flowed down slopes likegiant varicolored masses of taffy. These are mudflows and landslides.The colorful rocks are bounded on the south by gray and yellow tiltedlayers forming snowcapped peaks of the Gros Ventre Mountains.
These landscapes are the product of many naturalforces acting on a variety of rock types during long or short intervalsof geologic time. Each group of rocks records a chapter in the geologicstory of the region. Other chapters can be read from the tilting,folding, and breaking of the rocks. The latest episodes are written onthe face of the land itself.
Most park visitors first see the Teton peaks from thehighway. Whether they drive in from the south, east, or north, there isone point on the route at which a spectacular panorama of the Tetons andJackson Hole suddenly appears. Part of the thrill of these three viewsis that they are so unexpected and so different. The geologic history isresponsible for these differences.
View north.—Throughout the first 4 milesnorth of the town of Jackson, the view of the Tetons from U. S. 26-89 isblocked by East Gros Ventre Butte. At the north end of the butte, thehighway climbs onto a flat upland at the south boundary of Grand TetonNational Park. Without any advance warning, the motorist sees the wholeeast front of the Teton Range rising steeply from the amazingly flatfloor of Jackson Hole.
From the park boundary turnout no lakes or rivers arevisible to the north but the nearest line of trees in the direction ofthe highest Teton peaks marks the approximate position of the GrosVentre River. The elevation of this river is surprising, for the routehas just come up a 150-foot hill, out of the flat valley of a muchsmaller stream, yet here at eye-level is a major river perched on anupland plain. The reason for these strange relations is that the hill isa fault scarp (see fig. 16A for a diagram) and the valley in which thetown of Jackson is located was dropped 150 feet or more in the last15,000 years.
On the skyline directly west of the turnout arehorizontal and inclined layers of rocks. These once extended over thetops of the highest peaks but were worn away from some parts as themountains rose. All along the range, trees grow only up totreeline (also calledtimberline—a general elevationabove which trees do not grow) which here is about 10,500 feet above thesea. To the southeast and east, beyond the sage-covered floor of JacksonHole, are rolling partly forested slopes marking the west end of theGros Ventre Mountains. They do not look at all like the Tetons becausethey were formed in a very different manner. The Gros Ventres are foldedmountains that have foothills; the Tetons are faulted mountains that donot.
Three steepsided hills calledbuttes rise outof the flat floor of Jackson Hole. They are tilted and faulted masses ofhard, layered rock that have been shaped by southward-moving glaciers.Six miles north of the boundary turnout is Blacktail Butte, on theflanks of which are west-dipping white beds. Southwest of the turnout isEast Gros Ventre Butte, composed largely of layered rocks that areexposed along the road from Jackson almost to the turnout. These arecapped by very young lava that forms the brown cliff overlooking thehighway at the north end of the butte. To the southwest is West GrosVentre Butte, composed of similar rocks.
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View west.—The motorist traveling westalong U. S. 26-287 is treated to two magnificent views of the TetonRange. The first is 8 miles and the second 13 miles west of TogwoteePass. At these vantage points, between 20 and 30 miles from themountains, the great peaks seem half suspended between earth andsky—too close, almost, to believe, but too distant tocomprehend.
Only from closer range can the motorist begin toappreciate the size and steepness of the mountains and to discern thedetails of their architecture. The many roads on the floor of JacksonHole furnish ever-changing vistas, and signs provided by the NationalPark Service at numerous turnouts and scenic overlooks help the visitorto identify quickly the major peaks and canyons and the principalfeatures of the valley floor. Of all these roadside vantage points, thetop of Signal Mountain, an isolated hill rising nearly 1,000 feet out ofthe east margin of Jackson Lake, probably offers the best overallperspective (fig. 3). To the west, across the shimmering blue waters ofJackson Lake, the whole long parade of rugged peaks stretches from thenorth horizon to the south, many of the higher ones wearing the tatteredremnants of winter snow. From here, only 8 miles away, the toweringpinnacles, saw-toothed ridges, and deep U-shaped canyons are clearlyvisible.
Unlike most other great mountain ranges, the Tetonsrise steeply from the flat valley floor in a straight unbroken line. Thehigh central peaks tower more than a mile above the valley, butnorthward and southward the peaks diminish in height and lose theirjagged character, gradually giving way to lower ridges and roundedhills. Some of the details of the mountain rock can be seen—gnarledgray rocks of the high peaks threaded by a fine white lacework of dikes,the dark band that cleaves through Mount Moran from base to summit, andthe light brown and gray layers on the northern and southern parts ofthe range.
At first glance the floor of Jackson Hole south ofSignal Mountain seems flat, smooth, and featureless, except for theSnake River that cuts diagonally across it. Nevertheless, even the flatsshow a variety of land forms. The broad sage-covered areas, low isolatedhills, and hummocky tree-studded ridges that form the foreground are allparts of the Teton landscape, and give us clues to the natural processesthat shaped it. A critical look to the south discloses more strangethings. We take for granted the fact that the sides of normal valleysslope inward toward a central major stream. South of Signal Mountain,however, the visitor can see that the Snake River Valley does not fitthis description. The broad flat west of the river should slope east butit does not. Instead, it has been tilted westward by downward movementalong the Teton fault at the base of the mountains.
View south.—About a million motoristsdrive south from Yellowstone to Grand Teton National Park each year. Asthey wind along the crooked highway on the west brink of Lewis RiverCanyon (fig. 1), the view south is every where blocked by dense forest.Then, abruptly the road leaves the canyon, straightens out, and one canlook south down a 3-mile sloping avenue cut through the trees. There, 20to 30 miles away, framed by the roadway, are the snow-capped Tetons,with Jackson Lake, luminous in reflected light, nestled against the eastface. This is one of the loveliest and most unusual views of themountains that is available to the motorist, partly because he is 800feet above the level of Jackson Lake and partly because this is the onlyplace on a main highway where he can see clearly the third dimension(width) of the Tetons. The high peaks are on the east edge; they rise7,000 feet above the lake but other peaks and precipitous ridges,progressively diminishing in height, extend on to the west for a dozenmiles (fig. 14). Giant, relatively young lava flows, into which theLewis River Canyon was cut, poured southward all the way to the shore ofJackson Lake and buried the north end of the Teton Range (figs. 13 and53). South of Yellowstone Park these flows were later tilted and broken,by the dropping of Jackson Hole and the rise of the mountains.
As in many pursuits in life, the greatest rewards ofa visit to the Tetons come to those who expend a real effort to earnthem. Only by leaving the teeming valley and going up into the mountainsto hike the trails and climb the peaks can the visitor come to know theTetons in all their moods and changes and view close at hand the detailsof this magnificent mountain edifice.
Even a short hike to Hidden Falls and InspirationPoint affords an opportunity for a more intimate view of the mountains.Along the trail the hiker can examine outcrops of sugary white granite,glittering mica-studded dikes, and dark intricately layered rocks.Nearby are great piles of broken fragments that have fallen from thecliffs above, and the visitor can begin to appreciate how vulnerable arethe towering crags to the relentless onslaught of frost and snow. Theroar of the foaming stream and the thunder of the falls are constantreminders of the patient work of running water in wearing away the"everlasting hills." Running his hand across one of the smoothlypolished rock faces below Inspiration Point, the hiker gains anunforgettable concept of the power of glacial ice and its importance inshaping this majestic landscape. Looking back across Jenny Lake at theencircling ridge of glacial debris, he can easily comprehend the size ofthe ancient glacier that once flowed down Cascade Canyon and emergedonto the floor of Jackson Hole.
The more ambitious hiker or mountaineer can seek outthe inner recesses of the range and explore other facets of its geology.He can visit the jewel-like mountain lakes—Solitude, Holly, andAmphitheater are just a few—cradled in high remote basins left bythe Ice Age glaciers. He can get a closeup view of the Teton Glacierabove Amphitheater Lake, or explore the Schoolroom Glacier, the tiny icebody below Hurricane Pass. He may follow the trail into Garnet Canyon tosee the crystals from which the canyon takes its name and to examine thesoaring ribbonlike black dike near the end of the trail. In Alaska Basinhe can study the gently tilted layers of sandstone, limestone, and shalethat once blanketed the entire Teton Range and can search for thefossils that help determine their age and decipher their history. FromHurricane Pass he can see how these even layers of sedimentary rock havebeen broken and displaced and how the older harder rocks that form thehighest Teton peaks have been raised far above them along the BuckMountain fault.
Of all those who explore the high country, it is themountaineer who has perhaps the greatest opportunity to appreciate itsgeologic story. Indeed, the success of his climb and his very life maydepend on an intuitive grasp of the mountain geology and the processesthat shaped the peaks. He observes the most intimate details—theinclination of the joints and fractures, which gullies are swept byfalling rocks, which projecting knobs are firm, and which cracks willsafely take a piton. To many climbers the ascent of a peak is achallenge to technical competence, endurance, and courage, but to thoseendowed with curiosity and a sharp eye it can be much more. As he standsshoulder to shoulder with the clouds on some windswept peak, such as theGrand Teton, with the awesome panorama dropping away on all sides, hecan hardly avoid asking how this came to be. What does the mountaineersee that inspires this curiosity? From the very first glance, it isapparent that the scenes to the north, south, east, and west arestartlingly different.
Looking west from the rough, narrow, weather-ravagedgranite summit of the Grand Teton, one sees far below him the layeredgray cliffs ofmarine sedimentary rocks (solidified sedimentoriginally deposited in a shallow arm of the ocean) overlapping thegranite and dipping gently west, finally disappearing under thecheckerboard farm land of Teton Basin. Still farther west are therolling timbered slopes of the Big Hole Range in Idaho. A glance at theforeground, 3,000 feet below, shows some unusual relations of thestreams to the mountains. The watershed divide of the Teton Range is notmarked by the highest peaks as one would expect. Streams in CascadeCanyon and in other canyons to the north and south begin west of thepeaks, bend around them, then flow eastward in deep narrow gorges cutthrough the highest part of the range, and emerge onto the flat floor ofJackson Hole.
In the view north along the crest of the Teton Range,the asymmetry of the mountains is most apparent. The steep east faceculminating in the highest peaks contrasts with the lower more gentlewest flank of the uplift. From the Grand Teton it is not possible to seethe actual place where the mountains disappear under the lavas ofYellowstone Park, but the heavily timbered broad gentle surface of thelava plain is visible beyond the peaks and extends across the entirenorth panorama. Still farther north, 75 to 100 miles away, rise thesnowcapped peaks (from north west to northeast) of the Madison,Gallatin, and Beartooth Mountains.
The view east presents the greatest contrasts in theshortest distances—the flat floor of Jackson Hole is 3 miles awayand 7,000 feet below the top of the Grand Teton. Along the junction ofthe mountains and valley floor are blue glacial lakes strung out likeirregular beads in a necklace. They are conspicuously rimmed byblack-appearing margins of pine trees that grow only on the surroundingglacial moraines. Beyond these are the broad treeless boulder-strewnplains of Jackson Hole. Fifty miles to the east and northeast, on thehorizon beyond the rolling hills of the Pinyon Peak Highlands, are thehorizontally layered volcanic rocks of the Absaroka Range. Southeast isthe colorful red, purple, green, and gray Gros Ventre River Valley, withthe fresh giant scar of the Lower Gros Ventre Slide near its mouth.Bounding the south side of this valley are the peaks of the Gros VentreMountains, whose tilted slabby gray cliff-forming layers resemble (andare the same as) those on the west flank of the Teton Range. Seventymiles away, in the southeast distance, beyond the Gros Ventre Mountainsare the shining snowcapped peaks of the Wind River Range, the highestpeak of which (Gannett Peak) is about 20 feet higher than the GrandTeton.
Conspicuous on the eastern and southeastern skylineare high-level (11,000-12,000 feet) flat-topped surfaces on both theWind River and Absaroka Ranges. These are remnants that mark the upperlimit of sedimentary fill of the basins adjacent to the mountains. Aplain once connected these surfaces and extended westward at least asfar as the conspicuous flat on the mountain south of Lower Gros VentreSlide. It is difficult to imagine the amount of rock that has beenwashed away from between these remnants in comparatively recent geologictime, during and after the rise of the Teton Range.
From this vantage point the mountaineer also gets aconcept of the magnitude of the first and largest glaciers that scouredthe landscape. Ice flowed southwestward in an essentially unbrokenstream from the Beartooth Mountains, 100 miles away, westward from theAbsaroka Range, and northwestward from the Wind River Range (fig. 57).Ice lapped up to treeline on the Teton Range and extended across JacksonHole nearly to the top of the Lower Gros Ventre Slide. The Pinyon Peakand Mount Leidy High lands were almost buried. All these glaciers cametogether in Jackson Hole and flowed south within the ever-narrowingSnake River Valley.
The view south presents a great variety of contrasts.Conspicuous, as in the view north, is the asymmetry of the range. Southof the high peaks of crystalline rocks, gray layered cliffs of limestoneextend in places all the way to the steep east face of the Teton Rangewhere they are abruptly cut off by the great Teton fault.
The flat treeless floor of Jackson Hole narrowssouthward. Rising out of the middle are the previously describedsteepsided ice-scoured rocky buttes. Beginning near the town of Jackson,part of which is visible, and extending as far south as the eye can seeare row upon row of sharp ridges and snowcapped peaks that converge atvarious angles. These are the Hoback, Wyoming, Salt River, and SnakeRiver Ranges.