Rounded Rocks On Hwy 87 Between Phoenix And Payson, Arizona
Rounded Boulders And The Biblical Flood
I often drive past piles of large granite boulders on my way to Northern Arizona on Hwy 87 between Phoenix and Payson. Many times I have heard creationists claim these could have only formed and been deposited by a flood of biblical proportions (image 1).
Spheroidal weathering is most common among coarse grained igneous rocks like the type of granite that has been exposed in places along Highway 87 between Phoenix and Payson, Arizona. Joints (or cracks) are formed in the granite as the area became uplifted and the sandstone above the granite eroded away reducing pressure on the underlying igneous rock. We can look at road cuts in the area and clearly see the layer of granite that lies below the surface (image 2).
Once the granite is completely exposed, chemical weathering begins to break down and change the granite into rounded shapes by affecting the minerals present in the rock. If you have ever seen a rusty nail you have witnessed the effects of chemical weathering. Many minerals that formed when these igneous rocks were deep inside the earth are unstable when exposed to the atmosphere. Minerals that form at the highest temperatures and pressures are the least stable at the surface. Chemical weathering can change these minerals to clay over thousands of years. The clay is easily eroded by the elements and the rock becomes rounded at the joints and on the exposed top and sides. I was able to take a photo of a perfect example of jointed rock with weathered spherical boulders directly above (image 3).
No worldwide flood was needed to create these rounded boulders, although that explanation might seem plausible to those untrained in geology. Flood geologists would have a hard time explaining why such boulders are ONLY found where granite has been exposed and there is no evidence they have moved other than by gravity since they were formed. You can go just a few hundred yards away from the exposed granite and find no boulders at all in the areas where the sandstone has not eroded (image 4).