文構造と、訳を教えて下さい

But as the trail curved around the mountain, the trees and foliage to her left disappeared and became flat rock and jutting stones.

But
as the trail curved around the mountain,
the trees and foliage (to her left) disappeared
and
(the scene of the trees and foliage) became flat rock and jutting stones.

ということです。
left は to her left = 彼女の左側に、というところの「左」という意味で、
became の主語は、ちょっと取りにくいですが、つまりは the trees and foliage だった景色が、ということです。