It has an oiliness, and always seems to occur near strata of barely-altered Cretaceous swamp not compressed enough to be coal. Yet I’ve heard many a desert rat say, “That’s rattler smell.” It has always made me aware of my ankles.
But it’s a plant. Thick, small, dark green leaves in pairs on a red stem. I couldn’t find it in Weeds of the West, but it looks like a vetch.