Mad River U- Day 11

Geomorphology of the Teton Range
“Trois Tetons” were the first words uttered by lonely French Canadian trappers when they glimpsed the majestic Teton Range in late in the eighteenth century. Particularly, referring to the Grand, Middle and South Teton peaks as “three nipples (breasts)” or “Trois Tetons” the trappers would proclaim in lustful agony (Smith and Siegel, 93). This paper will try to undress some of the mystery and history that shroud these beautiful peaks with hopes that the Tetons will be fully revealed in a better understanding of the morphological processes by which these peaks formed.


A keen observer of the mostly gneiss and granite Teton range will notice the stark difference in rock composition as compared to other surrounding limestone mountain ranges. This is because of the recent formation of the Quaternary rock that was uplifted about 13 million years ago. Compared with the 345 million year old Appalachian Mountains this is a relatively young mountain range. The Tertiary, normal fault block (shown in Figure 1) was born 13 million years ago and since then has violently been active in thrusting the Tetons up and dropping the Jackson Hole Valley because of the stretch and spread of the Intermountain Seismic Belt. The Rocky Mountains and Colorado Plateau sit East of the belt and to the West lie the Basin and Range Province (Smith and Siegel 92). These two regions are stretching apart and allowed the great erection of the Tetons through the birth of the Teton Fault. The granitic and metamorphic rock that make up the Teton Range date back to somewhere between 1.5 to 2.5 billion years ago. The limestone, sandstone, shale and dolomite sedimentary rock that make up surrounding mountain ranges were deposited by an ancient ocean that began to recede 540 to 245 million years ago forming the rock that make up the Gros Ventre mountain range (Covington and Ransmeier 5). So, from these dates we know that the uplift of the Teton Fault was so great as to expose the much older rock to majestic height and that the younger recently deposited rock was eroded away and re-deposited in the Jackson Hole valley. Although the Tetons rise 7000 vertical feet above the valley floor this does not account for the total activity of the fault in feet. If we were to add the total uplift and down thrust of both the Teton Range and Jackson Hole valley it would add up to over 33,000 feet! The valley floor has filled with deposits from volcanic ash, granite cobble and alluvium which cover much of the apparent activity of the fault (Smith and Siegel 94) figure 5.2).


Glaciation, large moving masses of ice and rock debri, carved out much of the mountain range and sculpted it to its distinct form today. This glaciation process occurred in 3 stages that lasted no later than 2 million years ago and ended about 14 thousand years ago. The glacial period ended when global temperatures rose 9-12 degrees Fahrenheit within this time huge glaciers deposited rock and debri from the upper mountains to the base of the Teton Range forming what we know today as Jenny Lake, Phelps Lake and Jackson Lake among many other features (Smith and Seigel 130). Some glaciers still exist today but these are not remnants from the million years old glaciers. They have come from a “little ice age” that occurred from the 1400’s to the 1800’s. For a brief time the earth cooled enough to allow glaciers to form mostly in the Mount Moran and have since melted to form the many lakes found in the area.


From the day they were discovered to the present the Teton Range has been enjoyed by thousands for its unmatched beauty and large “tetons” that offer to the visitor the awe inspiring nurture of mother nature. Let all who come to this majestic area milk it for all the many wonderful things the range has to offer from skiing to multi trad climbing routes there is something of interest to any party that comes her way.