According to Austin Elliott, an Oxford geo-scientist who knows these sorts of things, the Wasatch Fault is the world’s best-studied normal fault. Thus, people like Elliot know quite a lot about the seam in the Earth’s crust that defines the Wasatch Front. Most of us actually living on or near the Fault, however, don’t know squat. So here’s a short version of the essential info, without too many big scientific words.
The Wasatch Fault forms a boundary between the relatively stable North American plate and the collapsing crust of the Great Basin and Range to the west. Slowly, so slowly we seldom notice it, the Salt Lake Valley is sliding away to the west, slipping off the Wasatch Mountains earthquake by earthquake. That’s what’s happening and has been happening for millennia.
Of course, lots of other forces have been at work on the Wasatch, too, making the mountains we know now. Ancient glaciers formed the smooth U-shaped valleys. Much, much later, rivers cut V-shaped valleys as they found their way downhill to the Prehistoric Lake Bonneville and its remains, The Great Salt Lake, and carved the floor of the big valley between the Wasatch Front and the Oquirrhs. Erosion by wind, rain, snow, hail and avalanches have sculpted the rock, stripped it away and worn it down to dirt.
But the big work was done when the Wasatch Fault’s movement cut through the moraines, slicing through them and lifting them up into the steep, jagged cliffs that give us a view of the interior history of the Earth. You can see the Jurassic Period in the reddish rocks up Parley’s Canyon. Near the mouth of the canyon, Suicide Rock is a relic of the earlier Triassic age. Lower portions of Big Cottonwood Canyon have billion-year-old Precambrian rock. The exposed portion of Timpanogos is limestone and dolomite from the Pennsylvanian period, about 300 million years old. Little Cottonwood Canyon has relatively newer rock: A molten igneous mass bubbled up near the surface a mere 32 million years ago. This is the granite that was used to build the Salt Lake City Temple which came to be called “Temple stone.”
And our Fault is what caused the stair stepping Benches, defining the value of Valley’s real estate. The higher your house, the higher the price.
We’ve known about the Wasatch Fault in theory since the 1890s, but that hasn’t stopped us from building steadily on it and around with little heed to the whole earthquake thing. We all feel them occasionally, little shivers that cause the pictures on our walls to go crooked, harbingers of the big one to come.
