These boulders at Pinnacle Peak near Scottsdale, Arizona, are a result of spheroidal weathering. Granitic rocks develop joints in several directions which have the tendency to break into blocks. Weathering caused by wind erosion, mechanical breakdown from freeze/thaw cycles and the chemical weathering of the rocks, round the boulders even more thus creating this landform common in the Arizona desert areas. These rocks are primarily known as middle Proterozoic granitic and include granodiorite, tonalite, quartz diorite, diorite, and gabbro. These rocks commonly are characterized by steep, northeast-striking foliation. See Royse, Chester F., Michael F. Sheridan, and H. Wesley Peirce. Geologic Guidebook. 4, Highways of Arizona, Arizona Highways 87, 88 and 188. Tucson: University of Arizona, 1971. See also, Mineral Resources On-Line Spatial Data.
This type of granitic rock is widely distributed in Arizona with outcrops in 11 of the counties.
I have always been interested in these granitic rocks as rocks. At first, because of the unusual forms and later, as I learned more about the geology, I became more interested in how they fit into the geological structure of the landforms.
This type of granitic rock is widely distributed in Arizona with outcrops in 11 of the counties.
I have always been interested in these granitic rocks as rocks. At first, because of the unusual forms and later, as I learned more about the geology, I became more interested in how they fit into the geological structure of the landforms.
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