If it's raining, and that's most of the time, the rock face of the mountain on the west side of the valley is almost covered with cascading water.
(that; 's; most of the time) (the rock face of the mountain on the west side of the valley; is almost covered; with cascading water)
that the rock face of the mountain on the west side of the valley
's is almost covered
most of the time
with cascading water