The 22-km-diameter Valles caldera is the world's type resurgent caldera and is host to a 280°C liquid-dominated hydrothermal system [Smith and Bailey, 1968; Goffand Gardner, 1994]. The caldera also contains various lacustrine sediments and hydromagmatic deposits dating from the inception of caldera formation to roughly 50 ka. More recent bog deposits are also present. Many of these deposits are presumably buried within the caldera moat and overlain and interbedded with post-caldera moat rhyolite eruptions. New geologic mapping at the 1:24,000 scale shows that the best exposures of lacustrine rocks occur on the uplifted flanks of the central resurgent dome [Goff et al., 2003] and as eroded remnants within the encircling valleys.