Joad speeded his pace against the sun, and he started down the declivity.
There are no more uses of "declivity" in the book.
Show samples from other sources
One Heart Breaking "There is a passion for declivity in this world," Tennessee Williams has one of his characters say in Comino Real. The ultimate declivity is death. But the pain that accompanies this descent in Williams’ plays is a sense of what is lost during the journey—honor, gentleness, tenderness, brotherhood, the ability to love, or even communicate with, another human being.
One Heart Breaking, Time Magazine, 1/19/70 -- http://www.time.com/time/magazine/article/0,9171,878685,00.html(retrieved 08/15/09)
Physical declivity takes her from a cane to a walker to a wheelchair.