Everything in this poem happens fast. A gray fox stands on a stonepile, and then it's gone. The speaker blinks again and the whole forest seems to vanish, leaving only a faint afterimage and a pair of cold, technical words in parentheses: "biomass" and "overburden." Those words suggest how easily a living place can be flattened into a resource or a pile of material to be cleared away.
What remains is sound. A drumming grouse beats its wings, and the speaker describes the noise as a "cellar hole" and a "palpitation," as if the dark and the heartbeat had become one thing. The sound is then compared to something heavy dropped from a height, bouncing a little less each time until the bounces blur into a roll.
The mood is uneasy and breathless, with a quiet sense of loss. The speaker seems to watch the world slip away and can only describe it, ending on the flat, detached idea of inertia.