To refer to the highest point on a hill, one might use the word "crest":
He walked up to the crest of the hill, and surveyed his surroundings.
On the other hand, one might also use "crest" as a verb to describe the action of crossing over the top of that hill:
She looked around as she crested the hill.
I feel as if there should be an equivalent noun/verb pairing to refer specifically to the action of crossing through the bottom of a valley, but I have been unable to find any reference to such a word. Does one even exist?
Examples of base nouns I've considered: