DELINEATION OF ADDITIONAL VOLCANIC CENTERS AND STRATIGRAPHIC VARIATIONS IN BIG BEND NATIONAL PARK, TEXAS
Additional volcanic vents and volcanic materials have been remapped as summarized below. Both intrusive and extrusive materials have been noted around Cerro Castellan that possibly are related to a lava dome. A small volcanic structure on the north end of Burro Mesa contains materials that are, at least in part, younger than the Tule Mountain Trachyandesite Member (Ttmt) of the Chisos Formation. Feeder dikes and numerous layers of Ttmt are found along Punta de la Sierra and hence are likely related to a volcanic source. A small mafic plug at Croton Spring Road contains both intrusive and extrusive components that may be a source for mafic lavas within the Chisos Formation. A few other stratigraphic variations have been documented. In the northern part of Burro Mesa there occurs at least one previously-unmapped mafic lava flow above Tmet. In several areas around the Sierra Quemada, additional pyroclastic flow deposits apparently not related to Tmet are found below and slightly above the Bee Mountain Basalt Member of the Chisos Formation. Finally, faults, mostly minor, are more abundant than previously mapped.