The Coconino Sandstone is the first great barrier you encounter as you descend into the Grand Canyon. In most places the Coconino forms a very steep, impassable cliff, up to 500 feet in height. The highest Coconino cliffs are along the South Rim in the eastern portion of the park. The cliffs are somewhat lower along the North Rim, and as you move from east to west they gradually become lower, but never less than 150 feet.The finest spot to see the Coconino cliffs up close is about a mile down from the rim on the Bright Angel Trail, at Tunnel #2. The trail follows switchbacks through a narrow break in the Coconino cliffs formed by the Bright Angel Fault, and you stay very close to unbroken, massive cliffs to both your left and right. Another excellent spot to see the Coconino cliffs that can be hiked to easily is the Coconino Overlook on the North Kaibab Trail, one mile down from the rim. The South Bass Trail has another fine view of the Coconino cliffs trailing away from you to the west as you pass through the break in the Coconino. The easiest way to know that you are in the Coconino is to locate a nearby Coconino cliff band and see if it is level with you. Here we are looking from the South Kaibab Trail back across Pipe Creek Canyon to the cliffs below Mather Point. The Coconino is the second large cliff band down from the rim, You can pick it out as the tannish colored cliff band that is the widest band near the rim, with a sloping area (the Toroweap Formation) above it, and another sloping area (the Hermit Shale) below it. In this picture the sloping areas are white with snow that has collected on their slopes. But take just a few hikes into the canyon as far down as the Coconino and you will quickly learn to recognize the Coconino close up. It has a light, tannish color, with distinct layers. But the layers are not neatly stacked vertically. The Coconino looks just like what it is – sand that was piled up into dunes, and has layers that weave and bob into one another at odd oblique angles, just like you see in sand dunes. And that’s just what the Coconino is: sand dunes that were formed some 275 million years ago.
The Coconino is so hard and the cliffs that it forms so steep that it usually takes some sort of fault line to break it up and form a route that a trail can follow. Locations where trails pass through the Coconino on such a fault are on the Bright Angel, North Kaibab, North Bass, and Tanner trails. But the cross-bedded nature of the Coconino also creates places where big blocks within the formation predominately slope in the same direction, which can then form a slope of blocks instead of a cliff, and a trail route can then pick its way through the blocks. Trails where you see this include the Hermit, South Bass, and New Hance trails. As you get further west in the Grand Canyon and the Coconino layer thins a bit, you find places where big debris fans coming down from formations higher up have entirely covered stretches of the Coconino, forming an easy route, as happens on the Jim Hall and Thunder River trails.
To read more detailed geological information about the Coconino Sandstone, visit the United States Geological Service page on the Coconino.