The Tapeats Sandstone is the bottom layer of the nine major formations horizontally stacked on top of one another, beginning with the Kaibab Limestone at the rim of the canyon. The Tapeats sits on top of the Great Unconformity, the great missing geological time gap of the Grand Canyon, first identified and named by John Wesley Powell during his initial exploration of the canyon in 1869. The Tapeats was deposited in a warm, shallow tropical sea over 500 million years ago, piling up on rocks beneath the waves that back then were already over a billion years old.
The formations beneath the Great Unconformity are not so neatly stacked. Another set of sedimentary rocks under the Great Unconformity, the Grand Canyon Supergroup, has its own stacking order, but its layers are not horizontal. Huge ancient geological processes, which many geologist now believe were part of the breakup of the supercontinent Rodinia 750 million years ago, tossed the layers of the Supergroup into all kinds of odd angles in different areas of the Grand Canyon. And underneath the Supergroup lies the oldest rocks of all, the Vishnu Complex, a mishmash of granite and metamorphic rocks, heated and twisted like taffy deep underground sometime in the ancient geologic past.Yet despite all the odd angles and complexity of the rock formations below the Great Unconformity, the entire area where the Tapeats Sandstone was formed had been ground down to a remarkably flat and uniform plain by the time the sea that formed the Tapeats invaded and covered the area. Here we are standing on top of the Tapeats near the Tonto Trail, on the rim of the inner canyon gouged out by the Colorado River, looking across the river to the north. We see the flat layer of Tapeats Sandstone forming the north rim of the inner canyon on the other side of the river. The dark, crinkly layer rising up from the river is the Vishnu Complex. Above it we see the bottom layers of the Grand Canyon Supergroup, the Bass Limestone and the Hakatai Shale, slanting dramatically down towards the river. The Tapeats Sandstone layer is remarkably flat and uniform, but there were at least a few islands in the Tapeats Sea. Here, along the New Hance Trail, we can see one of those ancient islands. You can see the Tapeats Sandstone coming in from the left of the picture, but notice that it gets thinner and thinner until at the center of the picture it is gone. A piece of the hardest rock in the Grand Canyon Supergroup, the Shinumo Quartzite, sticks up above it, not ground down enough in time to be under the water of the Tapeats sea. I find it fun to identify ancient geological islands like this while hiking along in the canyon; in time you can develop an eye to spot them. But to me the greatest pleasure that the Tapeats provides is the scenes that its rim offers to you. I only say offers, since most hikers never see them. When you hike along the Tonto Trail in the inner canyon, usually in the Bright Angel Shale set back just a bit from the Tapeats Sandstone rim, you pass through spectacular scenery provided by all the amazing temples, buttes, and ridges of the canyon rising up above you. But, unless you are willing to a make small investment of time and energy to wander a bit off the trail, you will just get brief glimpses of the Colorado river, and you will never see spectacular scenes like that of the river and Sockdolager Rapids you see above. Nor would you see this scene, the river flowing green instead of brown, looking back towards the temple of Isis below dark clouds massing above the North Rim. For me hiking the Tonto Trail, tracing the Tapeats Sandstone rim of the inner canyon above the Colorado River, is a wonderful movable feast, moving from one spot of spectacular scenery after another. Here we are at a spot that a lot of hikers do see – Plateau Point, which sits on the Tapeats Sandstone rim above the mouth of the canyon formed by Pipe Creek, with a spectacular view of the Colorado River flowing through the inner canyon. It is just an easy 30 minute stroll from the busy, popular campground at Indian Garden to get to it. But Plateau Point is just one of scores of other points close to the Tonto Trail along its entire length that offer equally spectacular scenes, witnessed by only a very few. Anywhere along the Tonto Platform where you have a point sticking out towards the Colorado River, and at each entrance to a major side canyon, both upstream and downstream along the Colorado River, you are likely to find such a scene. Here’s another one at a place I call Point 3808, which sticks out towards the Colorado from the Tonto Platform just west of Grapevine Canyon. To get to this spot, and to nearly all the others, you have to wander through the blackbush a little ways off the Tonto Trail, usually not more than a quarter mile. As you near the Tapeats Rim, the soft Bright Angel Shale will change over to big brown plates of Tapeats. If you hear the faint sound of distant rapids, you will know that the prize is near. Carefully work your way down just a little bit through the highest layers of the Tapeats, before you reach the cliffs, and you will be rewarded with another wonderful view of the Colorado and the inner canyon that you would have never seen from the trail. Most hikers camping along the Tonto Trail pitch their tents conveniently near a source of water. You usually find water, however, only at the head of side canyons, far from the spectacular scenes out on the points and side canyon entrances. I forego the convenience, and lug water out to a point and camp there, hoping for good shots in the best light in the late afternoon or early morning. Here are two panoramas shot out on Grand Scenic Divide Point, one late in the afternoon, and a second from the same exact spot following an overnight snowfall on the rim. For the wonderful scenes it offers, the rim of the Tapeats Sandstone is my favorite part of the canyon. But many times, at the head of side canyons, streams cutting though the Tapeats Sandstone create scenic narrow canyons, such as here along Hermit Creek, where the neatly stacked, softly rounded steep layers of the Tapeats are unmistakable. Some streams, such as Deer Creek, near its mouth on the north side of the Colorado, form much narrower, even more dramatic slot canyons in the Tapeats.
You can see many more dramatic panoramas shot from the Tapeats Rim by wandering along the Tonto Trail within the project. Or to read more detailed geological information about the Tapeats Sandstone, visit the United States Geological Service page for the Tapeats Sandstone.