The rocks are Permian limestones, laid down in warm, shallow tropical waters when Utah was about ten degrees north of the equator and the Kaibab Sea covered much of the western edge of ancient Pangaea. Over tens of millions of years, the future Utah would either have been submerged under a mere few meters of water or been barely above sea level.
I honestly do not know for sure if these blocks were quarried from the sedimentary rocks of the older Toroweap Formation or the overlying (and younger) Kaibab Formation, but I expect that the quarries are local. These two formations are quite prevalent in southwestern Utah near St. George, forming the massive Hurricane Cliffs along interstate 15 from near Cedar City south to Anderson Junction. Large tracts of Washington County countryside are Permian limestones, and the rocks can be followed further south into the extreme northwest corner of Arizona, again forming massive cliffs in the northern reaches of the Virgin River Gorge.
|Chert nodules in Kaibab limestone|
|Chert nodules in limestone|
|Silica replacing limestone in nodule|
Calcite is the common rock-forming mineral of calcium carbonate (or limestone). A drop or two from a small bottle of dilute hydrochloric acid comes in handy for checking the “fizz” of calcite and also limestone in general.
These limestones happen to be fairly fossil-rich, , too. Bryozoans, brachiopods, crinoids, corals, and sea urchins are commonly found. Bryozoans were (and still are) colonial animals which secreted a hard, limy skeleton. They are not the same as corals and are not plants.
These fossils in the chert nodule look like they might be bryozoans.
Brachiopods (below the penny) have been around for 500 million years. Many of the species became extinct at the end of the Permian Period (around
|Brachiopod (below penny)|
A few other items also caught my eye as I wandered about in this southern Utah yard… I could not identify this lizard, but wonder if that protrusion is its ear (between its eye and foreleg). Plus – check out those feet!