is this meant to be surreal? Is there some statement intended about the tides washing away the remains of humanity? Are the graves already underwater? Or is this perhaps a more familiar sort of landscape in some other part of the world that I’ve simply never seen?

I definitely agree with the first two sentiments. I don’t really see the water, I perceive it as more of a serene (because of the sheer scale of the hills made even more vast by them stretching beyond the ethereal fog) yet sinister (because of the forest of graves that swarm the ground) dreamscape.