“we should think of everest not as a mountain, but as the geologic embodiment of myth.” what do you think he means by that statement? in what way is everest a “chuck of myth”?

This is most likely a reference to the Everest's status as an unconquerable mission. Whenever we hear of "Everest," we are inclined to think of an extremely challenging and complex task that only few can accomplish. This is due to the status of Everest as the most difficult mountain to climb. It also has this legendary status in the culture of the people that inhabit the region. This makes Everest a type of myth for people who come in contact with it.

remember, the goal of an adjective clause is to add more information to a noun or a pronoun. as you can see from the examples above, you can add information by including a longer adjective clause or tighten up a sentence by turning the adjective clause into an adjective phrase.