A quick post as the semester wraps up (finally!), illustrating tafoni! Huzzah! The two pictures below are from the Wilkins Peak Member of the Green River Formation, in SW Wyoming.
Tafoni are scoopish-pits in granular rocks (like sandstones...) that are (probably) caused by weathering of differentially cemented zones in the rock.
And by the way, "tafoni" is apparently the plural...the singular is "tafone". Now you know!
EDIT: Yet more Tafoni on the internets! Check out Michael's post on his blog, Through The Sandglass!
EDIT EDIT: Jumpin' Cats! Michael is the Tafoni King at his blog...AND I HAD NO IDEA! Here and Here! Read!