yellowstone-morels_w Published November 15, 2018 at 2143 × 2400 in Yellowstone To Southwest Montana Autumn Field Photo Snaps Tertiary sediments and Quaternary sediments and basalts of “The Narrows” adjacent to the Yellowstone River, northern YNP. Columnar basalt capped by auto-brecciated basalt makes a morel-like image for these geological units.