Friday Field Foto: A little volcanic geopuzzle

Since it seems to be geopuzzle day, I thought I'd pitch in with something for the more igneous-inclined. (And it's an excuse to post a cool photo - always a good thing.)


So what's going on here? Click on the image for a larger version (somehow larger than I wanted, but it'll do for now). Wild conjecture and serious exposition are equally welcome; I'm going to withhold hints for the moment, since I don't know how easy or difficult this will be for everyone. (For a sense of scale, though, I will say that the two red rocks at the top left are about 4 or 5 cm wide.)

PS - If you've been to see these, no ruining it for the guessers. I'll throw in a poster of "Volcanoes in the National Parks" for the correct answer!