From my stat/sed prof....
"Slot canyons don't seem to be a speciality of anyone around WWU,
and I
don't know of any web sites specifically covering them or how they
form. (There are some pretty pictures out there, though.) I do know
that
they aren't restricted to sandstones, since I've seen them in limestone
and Doug remembers one in marble in Death Valley. In order to
form
a slot canyon, there must be rock that can be eroded but that is strong
enough to hold near-vertical slopes. It must also be relatively
homogenous, with no weak strata along which mass-wasting can cause
slope
failures. To the best of my knowledge, they are characteristic of arid
regions, as a guess, that could be because running water is restricted
rather than there being a lot of overland flow."
took her almost a month to say this....geologists are such slackers!