The soft, dark red rocks of the Hermit Shale formation form slopes that begin at the base of the Coconino Sandstone cliffs above it, and end where the top layer of the Supai formation, the Esplanade Sandstone, begins below it. Trails find routes through the Hermit Shale easily, with no cliffs to contend with and soft ground that will form a trail just about anywhere you want.The boundary between the Coconino and the Hermit Shale is quite remarkable. Here, on the North Bass Trail, we are just a few feet away from the boundary, and you can see that the rocks switch completely from the light tan Coconino to the dark red Hermit in just the space of a few inches. You might think that some huge environmental change took place in the geological blink of an eye to create this sharp boundary, but in fact there is an unconformity between the formations, meaning that the Hermit Shale was exposed on the surface and eroded away for some millions of years before the sands that formed the Coconino began to be deposited. You can also see that sharp boundary here, along a long traverse that the Boucher Trail follows though the Hermit Shale on its way out to Yuma Point. Also note the big blocks of Coconino littering the Hermit Shale slope. They come crashing down when the soft Hermit Shale erodes away and undermines the hard, resistant Coconino, and can turn a traverse across the Hermit into an obstacle course. You also see the ground here at your feet littered with small reddish blocks typical of the Hermit. In places where the Hermit Shale flattens out and forms a bit of a platform, scattered blackbrush contrast dramatically with the red Hermit Shale and form a beautiful scene, as here along the Dripping Spring Trail. The Hermit Shale formation thickens dramatically as you travel from east to west within the canyon. And that thickness has a dramatic effect on the character of the canyon. East of a tongue of land called the Grand Scenic Divide near the South Bass Trail, the Hermit Shale is fairly shallow, creating patterns of erosion that create the dramatic peaks and buttes that form much of the stunning beauty of the eastern canyon. West of the Grand Scenic Divide, however, the thicker layer of Hermit Shale erodes to form a wide shelf, the Esplanade, that dominates the western portion of the canyon. Here, looking down from the Kaibab Limestone near the rim along the Jim Hall Trail, we can see the wide, curving slope formed by the Hermit Shale, eroding away and exposing a wide area of Esplanade Sandstone. This wide expanse, from the lower, flatter portions of the Hermit Shale, and the flat upper portion of the Supai exposed where the Hermit Shale has eroded away completely, is the Esplanade.
To read more detailed geological information about the Hermit Shale, visit its page at the United States Geological Service.