Here are a few metaphors from the poem "David"

Lines 35-37

We crawled astride

The peak to feast on the marching ranges flagged

By the fading shreds of the shattered stormcloud. 

Hundred feet we fought the rock and shouldered and kneed Our way for an hour and made it.

Lines 49-52

...There it was too that David
Taught me to read the scroll of coral in limestone
And the beetle-seal in the shale of ghostly trilobites,
Letters delivered to man from the Cambrian waves

The coral in the limestone, the beetle-seal, and the ghostly trilobites are all fossils preserved in the sedimentary rock that David and Bob pass. The references to reading "the scroll" of fossils, "letters" from the Cambrian period, describes the wealth of information about ancient pre-history that can be gleaned from the fossils once you decode their 'language.'

Lines 138-139

The glistening hair of a creek on the rug stretched
By the firs, 

This is another visual metaphor. Picturing a creek as a hair on a green rug gives a sense David and Bob's height in the mountains; they are so far up that entire geographical features look as small and thin as hairs.