October 1

Like a sideways baseball cap, an irreverent patch of sandstone sits atop Mount Moran. Thousands of feet below, Jackson Lake reflects the young mountain so clearly that one can discern the cap and the wide black streak that scars its side. Mount Moran is growing. It is of the Teton Range in northwestern Wyoming, one of the youngest ranges in the Rockies, and it rises as a result of the Teton Fault. The Teton Fault is a colossal rip in the earth’s crust that appeared five million years ago. The rent runs north-south, and its appearance disrupted the equilibrium of the crustal blocks on each side of the damage. The western block tipped westward, and it hasn’t stopped tipping yet – the west side of the block is sinking and the east side is rising. On the other side of the Teton Fault, the crust sagged as the magma underneath it was diverted to Yellowstone Park, a few miles to the north, and it sags farther each day. The earth west of the Teton Fault towered above the earth on the other side, creating the Teton Mountains. But as the Tetons rose erosion weathered them down. Layer after layer was stripped from the peaks and washed into the basin below so that today, the topmost layer on Mount Moran is the sandstone cap that was deposited 500 million years ago – before animals learned to live on land. The corresponding layer on the other side of Teton Fault lies 25,000 feet – almost five miles – below. And the two sides continue to offset. Jenny Lake, which lies east of the fault, sank so fast in recent years that it took trees down with it, so that in 1986 divers in the 260-foot deep lake found tree stumps on the bottom. The peaks of the Tetons continue their thrust into the atmosphere even as wind, water and ice tear them down. Before long Mount Moran’s sandstone cap will disappear and the granite below will crest the mountain – the granite that bears Mount Moran’s defiant black scar, an intrusion of magma so ancient that it predates the first multicellular organism. The history of the earth is rising before our eyes.