These rocks, like the shale shown on the left, cleave in a uniform fashion… right along the layers. They become sharp as knives. Additionally the sedimentary layers of sand stone are sometimes folded upwards over time so that the edges are sticking straight up as pictured below. Driving over these is like driving on razor blades. Add to this the volcanic activity in the area and you have to deal with sharp lava rock too. The best way to avoid punctures is to look real close at the road ahead and drive real slow and have the best tires for your rig.

Most of Utah and Arizona was, at various times, an inland sea. Rivers fed it with runoff from the surrounding mountains. Every few thousand years a new layer of sand or shale was deposited on the old layers. Sediment hardens producing sand stone and shale layers. Uplift created the Colorado Plateau shown below left which is about in the middle of the ancient sea. Erosion exposed the sediments in cross section as seen in the image below right. If you have ever wondered why flag stone is so flat and even then maybe you can see how it got that way now.