The smooth and strong Kaibab Limestone makes contact with the soft, sloping Toroweap Formation beneath it. NPS Photo by Kristen M. Caldon

Kaibab Formation: Thickness: 200-500 ft.

Deposited 270 million years ago, during the Paleozoic Era - Early Middle Permian Period, the Kaibab Formation is the topmost rock layer at the Grand Canyon.

It is largely made up of light colored limestones and is a cliff forming unit. The Kaibab Formation contains numerous fossils indicative of a warm and shallow water environment, including crinoids, brachiopods, bryozoans, and sponges.

Chert, which forms irregular blobs and nodules, is common in the Kaibab. Chert is composed of silica and, as it is more resistant to weathering, can often be seen protruding from the rock around it.

It often forms where there is an empty space in the rock, such as in a worm burrow. It also forms where an organism made primarily of silica, such as a sponge, has been buried. Most of the sponges in the Kaibab Formation are preserved in chert.

The Kaibab Limestone is also distinct in that it is readily dissolved, resulting in the formation of karst topography on the canyon’s rims.

Numerous caves and sinkholes are present in the Kaibab, particularly on the North Rim. While the Kaibab Limestone now caps Grand Canyon’s rims, many more rock layers once sat above the Kaibab.