Wheat fields at sunrise in Teton Valley, Idaho on the western side of the Grand Tetons.
The Cathedral group of the Grand Tetons rose along a normal fault over the last 5 million years and were sculpted to their sharp angular form by glaciers over the last 2 million years with the last major glaciers receding 15,000 years ago. They are composed largely of quartz monzonite (a type of granite) which was the core of a previous mountain range that was raised by tectonic compressive forces 55 million years ago and then eroded. This metamorphic core of the mountains arose originally from volcanic and sedimentary rocks 2-3 billion years ago.
Major mountain peaks named.
Snake River with Grand Tetons in background. Snake River terraces are formed from glacial outwash gravels.
Mt. Moran with Jackson Lake in the foreground.
Mount Moran is composed of gneiss and granitic gneiss with dikes and sills of granite and pegmatite of igneous origin. A thick diabase dike running vertically throughout the mountain arose from basaltic magma intrusion into the older Precambrian metamorphic rock 600 million years ago.
From left to right: Teewinot, Grand Teton, Cascade Valley and Mt. St. John.
Teewinot Mountain.
