Geologically speaking, the Tetons are very young mountains. They are the youngest in the Rockies chain. They were formed by a crack (fault) running along the mountains’ eastern front. Earthquakes prompted the east fault to slide down, displacing the earth to the west. Imagine two saloon doors swinging in opposite directions and one slides into the other, thus pushing it wider. This is why there no foothills in the Tetons and why they are so sharp. The mountains just thrust sharply out of the earth. French trappers in the region (who, of course hadn’t been with women in a while) named the central trio of peaks “les Trois Tetons,” or, “the Three Breasts.” The resulting valley -or hole- created by the sinking eastern plate was named Jackson Hole by a trapper named Davey Jackson.
The Grand Tetons were made a National Park in 1950 and is about one-seventh the size of its neighbor to the north, Yellowstone N.P.