Arizona’s China Wall

October 12, 2022



Photographer: Thomas McGuire 

Summary Author: Thomas McGuire 

Shown above is China Wall, a rock formation in the Tonto National Forest, north of Scottsdale, Arizona. It forms a broken vertical wall nearly a mile long (1.6 km), and about 10 feet high (3 m) and 5 feet wide (1.5 m), draped over the summit of Bronco Butte (satellite photo below). It was so-named because of its resemblance to the ruins of the Great Wall of China, which is about two to three times larger.

China Wall is a sill intrusion of rhyolite, a relatively common igneous rock. Rhyolite has a composition similar to granite, but due to relatively rapid cooling, the crystals are much smaller than granite. The China Wall magma was injected into meta-sedimentary rocks that are nearly half as old as Earth itself. Although the layer of rock is oriented vertically, it’s inferred that the sill was injected horizontally and the whole regional package was rotated into the vertical position by a billion years of plate tectonic forces. With the sparse vegetation found in the U.S. Southwest, bedrock exposures often reveal the orientation of the layers.



Bronco Butte, Arizona Coordinates: 33.901794, -111.874248

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