Many sandstone cliffs, pillars, and boulders are
undercut towards their bases. In the case of
boulders and pillars, the undercutting produces
mushroom, perched, or pedestal rocks. Processes
invoked to account for the undercutting include
(1) the presence of softer and more effortlessly
weathered bands of rock; (2) abrasion by windblown
sand (cf. p. 317); (3) salt weathering
brought about by salts raised by capillary action
from soil-covered talus at the cliff base; (4) the
intensified rotting of the sandstone by moisture
rising from the soil or talus; and (5) subsurface
weathering that occurs prior to footslope lowering.