Visualize the Great Pyramids at Giza in Egypt. Giant blocks piled on top of one another that you must scramble up one after another to reach the top. That is how I think of the Supai Formation in the Grand Canyon.Here we see the Supai Formation along the North Kaibab Trail, with its characteristic reddish color, and tier upon tier of giant blocks. But there is a distinct pattern within the formation throughout the park which you can just make out here: a steep cliff at the top, the Esplanade Sandstone, a section of sloping tiers below it, the Wescogame Formation, then a second major cliff band, the Manakacha Formation, and finally a second sloping area below that, the Watahomigi Formation, ending at the top of the Redwall Limestone. Everywhere you go in the park the color and blocky nature of the entire Supai remains the same, but the proportions of the sublayers vary tremendously. Here, on the Nankoweap Trail, the Esplanade Sandstone cliff is huge, and remains that way for the entire length of a 4 mile traverse the trail makes clinging to a narrow sloping area at its base. A large number of other trails also have long traverses in the Supai, as they head for a spot to finally pass though the Redwall.
In the western portion of the park, a thick layer of soft Hermit Shale erodes away and exposes a wide shelf of Esplanade Sandstone at the top of the Supai that erodes, like here along the Thunder River Trail, into lovely and sensuous shapes. This pattern of erosion also creates depressions where rainwater will collect into welcome pools that can persist for quite some time in the cooler months, but disappear almost immediately in summer heat.
Here, along the Thunder River Trail, it is the Manakacha Formation that forms the highest cliffs within the Supai. As you near the boundary between the Supai and the Redwall Limestone below it, you may begin to see outcrops or narrow cliff bands of flinty, gray stone that may make you think that you have already slipped down into the Redwall layer. But it is more likely that, like here on the South Bass Trail, you remain in the Watahomigi at the base of the Supai. There’s what looks like a transition zone at the bottom of the Watahomigi into the Redwall, but in fact there is time gap between the formations of some 15 to 20 million years. But you know with certainty, that you’re in the Redwall when you reach the high cliffs. The Supai tends to erode into large blocks, like you see here on top of Cardenas Butte along the Tanner Trail. As you gain experience as a Grand Canyon hiker, you learn to recognize Supai rocks that have made their way down much deeper into the canyon and you are grateful for them: big Supai boulders far from their home higher up in the canyon often create a welcome resting spot for you and your backpack.
To read more detailed geological information about the Supai Formation, visit its page at the United States Geological Service.