Big Obsidian Flow, Oregon

If we head north, we reach another bimodal caldera that sits behind the main arc of Cascade volcanoes -- this time, Newberry Caldera in Oregon. On the southern wall of the caldera spreading into the caldera itself is the aptly named Big Obsidian Flow that erupted ~1320 years ago. When this flow was erupted, it produced pyroclastic flows that spread down towards Paulina Lake (and two campgrounds are built on the Big Obsidian Flow deposits). The Big Obsidian Flow is nearly aphyric -- meaning you'd be hard-pressed to find any crystals in it (and trust me, I've looked at it hoping to get zircon) -- meaning it was likely hot when this rhyolite lava erupted, preventing many (if any) crystals from forming in the lava.

Image: USGS