Fig. 6. (a) Exposures of Bandelier Tuff on the south face of Mesita del Buey at MDA G. Qbt 2, which forms the resistant caprock of the mesa, is made up of moderately welded ash-flow tuffs with numerous high-angle joints. Qbt 1vu is the lighter colored, sloping unit in the lower part of the outcrop. Qbt 1vu is made up of non- to partly welded ash-tuffs with fewer fractures. (b) The sandy surge deposits that occur at the base of Qbt 2. The surge bed is a cross-bedded sandy deposit that is overlain by a nonwelded pumice-rich ash-flow tuff. The 13.5-cm-long pen is for scale.