The site of the Teton block no doubt reflects hidden inequalities at depth. We cannot see these, nor in this area can we drill below the outer layer of the earth; nevertheless, measurements of gravity and of the earth’s magnetic field clearly show that they exist.
We know that the Tetons rose at the time Jackson Hole collapsed but the volume of the uplifted block is considerably less than that of the downdropped block. This, then, was not just a simple case in which all the subcrustal material displaced by the sinking block was squeezed under the rising block (the way a hydraulic jack works). What happened to the rest of the material that once was under Jackson Hole? It could not be compressed so it had to go somewhere.
As you look northward from the top of the Grand Teton or Mount Moran, or from the main highway at the north edge of Grand Teton National Park, you see the great smooth sweep of the volcanic plateau in Yellowstone National Park. Farther off to the northeast are the strikingly layered volcanic rocks of the Absaroka Range ([fig. 52]). For these two areas, an estimate of the volume of volcanic rock that reached the surface and flowed out, or was blown out and spread far and wide by wind and water, is considerably in excess of 10,000 cubic miles. On the other hand, this volume is many times more than that displaced by the sagging and downfaulting of Jackson Hole.
Where did the rest of the volcanic material come from? Is it pertinent to our story? Teton Basin, on the west side of the Teton Range, and the broad Snake River downwarp farther to the northwest ([fig. 1]) are sufficiently large to have furnished the remainder of the volcanic debris. As it was blown out of vents in the Yellowstone-Absaroka area, its place could have been taken deep underground by material that moved laterally from below all three downdropped areas. The movement may have been caused by slow convection currents within the earth, or perhaps by some other, as yet unknown, force. The sagging of the earth’s crust on both sides of the Teton Range as well as the long-continued volcanism are certainly directly related to the geologic history of the park.
In summary, we theorize as to how the Tetons rose and Jackson Hole sank but are not sure why the range is located at this particular place, why it trends north, why it rose so high, or why this one, of all the mountain ranges surrounding the Yellowstone-Absaroka volcanic area, had such a unique history of uplift. These are problems to challenge the minds of generations of earth scientists yet to come.
The restless land
Among the greatest of the park’s many attractions is the solitude one can savor in the midst of magnificent scenery. Only a short walk separates us from the highway, torrents of cars, noise, and tension. Away from these, everything seems restful.
Quiescent it may seem, yet the landscape is not static but dynamic. This is one of the many exciting ideas that geology has contributed to society. The concept of the “everlasting hills” is a myth. All the features around us are actually rather short-lived in terms of geologic time. The discerning eye detects again and again the restlessness of the land. We have discussed many bits of evidence that show how the landscape and the earth’s crust beneath it are constantly being carved, pushed up, dropped down, folded, tilted, and faulted.
The Teton landscape is a battleground, the scene of a continuing unresolved struggle between the forces that deform the earth’s crust and raise the mountains and the slow processes of erosion that strive to level the uplands, fill the hollows, and reduce the landscape to an ultimate featureless plain. The remainder of this booklet is devoted to tracing the seesaw conflict between these inexorable antagonists through more than 2.5 billion years as they shaped the present landscape—and the battle still goes on.
Evidence of the struggle is all around us. Even though to some observers it may detract from the restfulness of the scene, perhaps it conveys to all of us a new appreciation of the tremendous dynamic forces responsible for the magnificence of the Teton Range.