Down in those vine maples, you can see the contact between the edge of the Collier Cone Lava Flow (right) and the older, glacially carved, volcanic rock of the valley floor (left). The question is, has this contact been modified by rare to occasional burst floods from above the valley? It seems clear to me that there has been no such activity recently; the thick-bedded moss would not be so consistent. Likewise, there's some down logs in pretty advanced states of decay near the center of the photo. Any recent (past decade or so) would have left both of those features more chewed up. The contact seems rounded, which might indicate erosional modification... but look at all that living and dead plant material! Surely that might be the explanation for the apparent rounding.
In the end, as is so often the case, the answer is, "I don't know; I need more information." I'm okay with that. It means I have a reason to go look again.