field seminar for the AAPG in Arizona and Nevada, and I saw some incredible things.
1.7 billion years ago, fragments of continental crust were colliding to form the core of a new North American continent. Those mountains climbed to the sky, rivaling the Himalaya or the Andes in their grandeur. The time was so ancient that not a bit of life existed on the mountain flanks. The only lifeforms at all were single-celled organisms in the oceans.
The forces pushing the mountains upwards ended, and the ice and rain tore away the flanks. The gigantic peaks eroded to hills, and in hundreds of millions of years, the hills eroded to nearly flat plains. They were gone, but the rocks that formed the roots of those mountains remained. Around 530 million years ago, the continent had begun to break up, and the edges subsided slowly while a shallow sea advanced. The beach sands swirled back and forth across the roots of the ancient mountains.
The problem with the Great Unconformity, as the early geologists called it, is that it is mainly exposed in the bottom of the Grand Canyon. There are only a few ways to see it and touch it: you can float down the Colorado River in a raft, or you can walk down the long difficult trails from the rim of the canyon. Or, as it turns out, you can drive.
If the exposure lacks anything, it is grandeur. The oldest rocks of the Grand Canyon are at the bottom of one of the deepest and longest gorges in the world, and there is much to be said for seeing the rocks in their full perspective, underneath a mile of subsequent sedimentary layers. When time or health is short, hiking or rafting is not feasible. But I was on a mission today, to see the only place in all of the Grand Canyon where one can drive to the Great Unconformity. It is well-known to rafters as it is the take-out point for the river voyagers. It's called Diamond Creek, and Peach Springs Canyon. The road starts at the administrative headquarters of the Hualapai Nation in Peach Springs, and winds 19 miles and 3,500 feet down to the Colorado.
Heading deeper into the canyon, we see some evidence of deformation; in the picture below, we can see a gentle monocline crossing the picture where the layers step down in elevation without splitting. A major fault zone, the Hurricane fault, crosses the canyon in front of the fold. The road turns and follows the fault zone.
I zoomed up the road, picked up Mrs. Geotripper, and sped on to Williams without turning the car off once. Thus, our unexpected night in a motel, and a delay, looking for a saturday mechanic before we head on to Grand Canyon tomorrow. And internet access! We'll see what surprises tomorrow holds for us.
By the way, the ocotillos were blooming in the lower canyon...enjoy!