slot canyon on north shore follow eroded basalt dykes in granite. true slots with up to 100 foot deep, 5 foot wide canyon in places.
slot canyon in new zealand in all sorts of non sandstone rocks.
granite slot canyons in christmas tree pass area (granite) SE of vegas.
whoever said you gotta have sandstone to slot canyon has his head up his ass geologist or no. all you need is an eroded canyon much deeper than it is wide. hell the north gully of the chief is almost a slot canyon except that it isnt water eroded. there are some wicked almost-slots descending to the squamish highway that one day it will freeze enough to climb on ice all the way from the highway to the summit.
lots of these type of features up near lillooet too (in limestone) and in the cdn rockies ( in limestone).