Re: California Geology Magazine
Posted by Kent on December 18, 2001 at 18:16:59:
In Reply to: California Geology Magazine posted by dave on December 12, 2001 at 22:08:34:
Hey Dave, came across this on a geology instructor's web site:
"Mushroom rock (picture) got its name from its unusual shape. The narrowing at the base is formed from small, wind blown sand grains wearing away at the base of the rock. The top of the rock is not effected because the sand rolls and bounces along the ground, and cannot be lifted that high. The rock itself is a basalt. Basalt is a very dense, black, rock that is derived from the mantle. It is here because the faulting is very deep rooted, allowing mantle material to penetrate the crust. The denser basalt is causing the valley floor to drop lower, and has the potential to transform the basin floor into a more ocean like crust."
So, the base of Mushroom Rock could be considered a ventifact, but the top isn't. ;-)