The Kaibab Limestone

In Northern Arizona

(Uploaded 12/27/08)

Covering most of Northern Arizona from the south edge of the Mogollon Rim to the highlands north of Flagstaff, the Permian Kaibab Limestone is part of the Kaibab Formation, which includes sandstones, shales, mud stones and dolomites. The Kaibab is 260 to 255 million years old, and is perched on the Coconino and Toroweap sandstones. We have found much of the limestone is really dolomite, and much of the fossiliferous type is fetid. (produces a petroleum like odor when struck with a rock pick) The Kaibab contains two basic members, the upper Harrisburg member which consists of the older alpha member, and the lower Fossil Mountain member which is derived from the older terminology beta and gamma members. The lithology of each is distinctly different, the Fossil Mountain occurring on the southern edge of the Mogollon Rim, and contains mostly productid brachiopods, burrows of callanassid shrimp, and hexactanellid sponges. The upper Harrisburg member is highly dolomitic, and contains fossils of clams, cephlopods, and brachiopods.


A very scenic panorama of Blue Ridge reservoir, a very good outcrop of the Kaibab Fossil Mountain member. The lake itself is a manmade affair, complete with a boat launch and fish. Examination of the lithology of the area is made much easier by the fine road that cuts through the outcrop, along the lake. We have collected both molluscs, productids, trilobites and sponges at this site, although it is only locally fossiliferous.

Many of the best outcrops of the Fossil Mountain member can be found on the west end of Lake Mary Road up near Flagstaff. It was along this road we found several giant football sized nautiloids, trilobites, sponges, and a variety of brachiopods. The road itself also cuts through a great deal of basalt on the east end, with a bit of Triassic Moenkopi about in the middle.

Numerous low cliffs of Fossil Mountain member Kaibab limestone can be found in the Rim town of Heber. Just north of town is a huge canyon, with many outcrops and exposures. Fossils include large numbers of sea urchin spines, sponges and productids.

Another fine exposure just north of Heber, in the main canyon. Here we can see the more massive cliff forming material overlying a debris slope of softer less resistant material eroding away. Often the more resistant facies are composed of dolomite.

Down Forest Road 86 out of Heber, we find a large number of unique isolated outcrops framed by numerous conifer trees. This exposure of the Fossil Mountain member shows differential weathering of the different levels from a pure white to a dark dingy gray color.

This magnificent outcrop of Fossil Mountain member is down Forest Road 86 outside of Heber. Differential weathering seen here as a dark massive member, and a less resistant crumbling bed in between. We found brachiopod fossils at the base of the cliff, which appeared to originate from the less resistant beds. This is one of our favorite outcrops for its natural beauty.

This road cut was found down Forest Road 86 just outside of Heber. It is unusual because the huge amount of pure white sand that was eroding out of the layers, which were strongly cross bedded, indicating a beach dune deposit or sand bar. The white sand was followed for hundreds of feet down the road which washed out during recent rains. This was a non fossiliferous unit of the Fossil Mountain member.

A close up view of the above road cut, showing the bedding pattern in more detail. The individual slabs were extremely sandy, more of a very sandy limy shale, and pure white sand poured out as you broke the layers apart. Upon seeing the white beach sand in the road, I couldn't help but image the roaring ocean waves that were at one time at this location, and now, 285 million years later I was standing on the ancient sands, now totally silent.

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