I was struck by the same thing.
The land looked completely parched.
Then I thought, well, 1967, maybe they burned everything down or used defoliants to stop infiltration.
I haven’t been to the central highlands, but the hills do resemble the pictures I’ve seen, just minus all the trees and vegetation.
laterite probably. once the soil is removed (by scrapers
or Rome plows) the ground hardens into a red clay that tints everything and is hard as cement. you could tell who was out in the field longest by the redness of their fatigues.