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The Geologic Map of the Mount Taylor Volcano Area, New Mexico is a 1:36,000 compilation of six recent NMBGMR 1:24,000 geologic quadrangles that encompass this extinct composite stratovolcano. Mount Taylor is New Mexico's second-largest volcano after the Valles Caldera in the Jemez Mountains. This timely map and accompanying report, resulting from over a decade of thorough work, synthesizes the current geologic understanding of such an important landscape feature of the state.For such a complex volcanic landform, the report provides an exhaustive description of the volcano area in an easy-to-read format. In addition to providing a detailed description of each of the map's 339 units and dikes, it documents the volcano's history and history of research, its geochemical and petrographic composition, the phases of its construction ranging from the initial to the terminal eruptions, 3.72-1.26 million years ago, and its subsequent erosion, resulting in the summit Amphitheater and its extensive apron of debris. It describes the surrounding volcanic centers, the structure of the area, and the extensive dikes and maars. After touching on the water resources, hydrothermal alteration and mineralization, and geothermal potential, the report concludes with a conceptual model of volcano evolution.

Quantitative X-ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the Valles caldera resurgent dome. The alteration assemblage consists primarily of smectite–clinoptilolite–mordenite–silica, which replaces groundmass and fills voids, especially in the tuffs and lacustrine rocks. Original rock textures are routinely preserved. Mineralization typically extends to depths of only a few tens of meters and resembles shallow “caldera-type zeolitization” as defined by Utada et al. [Utada, M., Shimizu, M., Ito, T., Inoue, A., 1999. Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan — with special reference to “caldera-type zeolitization.” Resource Geol. Spec. Issue No. 20, 129–140]. Geology and 40Ar/39Ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed (ca. 1.25 to 1.22 Ma). Zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water (a mixture of meteoric waters and degassed hydrothermal fluids) and by high thermal gradients caused by cooling of the underlying magma body and earliest post-caldera rhyolite eruptions. Zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat (≤ 0.8 Ma) suggesting that later lake waters were cooler and less alkaline. The shallow zeolitic alteration does not have characteristics resembling classic, alkaline lake zeolite deposits (no analcime, erionite, or chabazite) nor does it contain zeolites common in high-temperature hydrothermal systems (laumontite or wairakite). Although aerially extensive, the early zeolitic alteration does not form laterally continuous beds and are consequently, not of economic significance.

Many geothermal systems are intimately associated with intrusion and volcanism along convergent plate margins, within rifts, and at hot spots. Areas of active structural deformation, especially extension and transtension, localize shallow intrusion and favor formation and maintenance of fracture networks that promote convection of deeply circulated meteoric water. Such systems efficiently deliver heat and mass flow from the intrusive realm at depths >3 km to the Hydrosphere. Extensive fracture networks are formed and maintained by the interplay of tectonic stresses with magma emplacement, and the episodic expulsion of magmatic fluids during recharge, eruption, and crystallization. Hydrothermally driven fluid flow along upflow and outflow paths alters reservoir rocks to characteristic secondary mineral assemblages that reflect the chemistry and temperature of the system. A capping hydrothermal clay-rich layer commonly limits communication of deep (>0.6 km), high-temperature (220–350 °C) neutral-chloride brine from near-surface groundwater circulating above this altered zone. The chemical characteristics of fluids reaching the surface locally along structures, and the distribution of clay alteration as revealed by electrical resistivity surveys, are used to prospect for exploitable systems. Of all geothermal systems, those related to magmatic intrusion are the most prolific source of electricity worldwide. If properly developed and managed, they provide a very long-term source of indigenous energy without combustion of fossil fuels.