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Figure 20. Cartoon model showing evolution of the Caetano caldera. Sections are  N-S through the center of the caldera. No vertical exaggeration. (A) ca. 34 Ma shortly before caldera formation. Caldera site underlain by irregular erosional surface on Paleozoic rocks locally cut by Tertiary paleovalleys, partly filled with gravels and andesite lava flows. (B) 33.8 Ma following eruption of the thick lower unit of Caetano Tuff, caldera collapse with megabreccia blocks and meso-breccia lenses shed into the caldera, and eruption of the much thinner upper unit of Caetano Tuff. Caldera collapse was significantly greater in the eastern part of the caldera than in the western part. (C) 33.7 Ma following intrusion of the Carico Lake and Redrock Canyon plutons, resurgent doming around Carico Lake pluton, shedding of breccias off the resurgent dome, circulation of hydrothermal fluids and extensive hydrothermal alteration in western part of caldera probably related to the Redrock Canyon intrusion, and emplacement of small, ring-fracture intrusion; (D) 25.3 Ma following a long period of deposition of sediments and distal outflow tuffs (mostly Bates Mountain Tuffs) in caldera depression. Early sediments may have been lacustrine and deposited in a moat around the resurgent dome. Later sediments are mostly fluvial.
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' quadrangle). East-dipping Caetano Tuff and interbedded mesobreccia lenses composed of Paleozoic clasts (Fig. 13A) are abruptly truncated against Paleozoic Valmy Formation at west-northwest–striking, steeply north-dipping caldera margin. Upper mesobreccia consists of interbedded lenses of Paleozoic clast debris-flow deposits and lithic-rich Caetano Tuff (Fig. 13B). The Red Mountain fault steps abruptly westward at and probably reactivates the caldera boundary fault.
