Mushroom Rock is an interestingly shaped rock in Death Valley. This rock is fairly well known because it is located just by the road running from Furnace Creek to Badwater Basin (lowest point in the western hemisphere).
There are a number of similarly shaped rocks in the world. Most of them are shaped by wind-blown sand grains and are therefore ventifacts. There are some nice examples of ventifacts in Death Valley nearby (read my post about them: Ventifacts and dreikanters). However, this rock is probably shaped by salt erosion, not wind1. Crystallization of salt crystals can be an effective way to disintegrate rocks.
I read from several sources that the sign erroneously claims that Mushroom Rock is a ventifact (shaped by wind). There is no such sign anymore and not even a place to stop a car. Maybe because the rock was vandalized some years ago. It has been repaired and I did not notice anything wrong while I was there. So it must be a job nicely done.
Small holes in the upper part of the rock (mushroom cap) resemble tafoni to me and may also indicate that salt is responsible for eroding this rock.
Mushroom Rock is carved from igneous rock diabase with a nice porphyritic texture. White phenocrysts are plagioclase crystals. Width of the view is about 25 cm.
References
1. Miller, M. & Wright, L. A. (2012). Geology of Death Valley: Landforms, Crustal Extension, Geologic History, Road Guides