This dataset accompanies publication 'Geologic Map of the Poncha Pass Area, Chaffee, Fremont, and Saguache Counties, Colorado'.

This dataset accompanies publication "Geologic map of the San Antonio Mountain area, northern New Mexico and southern Colorado". Data presented here include the digital geologic database, 40Ar/39Ar geochronology and major and trace element chemistry from lava flows and an ignimbrite. The geologic database includes spatial feature classes and non-spatial tables that collectively contain the geologic information presented in the map plate. 40Ar/39Ar geochronologic analyses and geochemical data constrain temporal and stratigraphic relations for deposits associated with the Taos Plateau volcanic field, late Oligocene to Miocene basaltic volcanism, and the San Juan Mountains locus of the Southern Rocky Mountains volcanic field along the western margin of the San Luis Basin situated in northern New Mexico and southern Colorado, USA.

This dataset accompanies publication "Geologic map of the San Antonio Mountain area, northern New Mexico and southern Colorado". Data presented here include the digital geologic database, 40Ar/39Ar geochronology and major and trace element chemistry from lava flows and an ignimbrite. The geologic database includes spatial feature classes and non-spatial tables that collectively contain the geologic information presented in the map plate. 40Ar/39Ar geochronologic analyses and geochemical data constrain temporal and stratigraphic relations for deposits associated with the Taos Plateau volcanic field, late Oligocene to Miocene basaltic volcanism, and the San Juan Mountains locus of the Southern Rocky Mountains volcanic field along the western margin of the San Luis Basin situated in northern New Mexico and southern Colorado, USA.

This geodatabase contains all the geologic map information for the Geologic Map of the San Juan caldera cluster, southwestern Colorado and is part of U.S. Geological Survey Geologic Investigations Map Series I-2799. The San Juan Mountains are the largest erosional remnant of a composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time. The San Juan field consists mainly of intermediate-composition lavas and breccias, erupted about 35-30 Ma from scattered central volcanoes (Conejos Formation) and overlain by voluminous ash-flow sheets erupted from caldera sources. In the central San Juan Mountains, eruption of at least 8,800 km3 of dacitic-rhyolitic magma as nine major ash flow sheets (individually 150-5,000 km3) was accompanied by recurrent caldera subsidence between 28.3 Ma and about 26.5 Ma. Voluminous andesitic-dacitic lavas and breccias were erupted from central volcanoes prior to the ash-flow eruptions, and similar lava eruptions continued within and adjacent to the calderas during the period of more silicic explosive volcanism. Exposed calderas vary in size from 10 to 75 km in maximum dimension, the largest calderas being associated with the most voluminous eruptions.

This geodatabase contains all the geologic map information for the Geologic Map of the San Juan caldera cluster, southwestern Colorado and is part of U.S. Geological Survey Geologic Investigations Map Series I-2799. The San Juan Mountains are the largest erosional remnant of a composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time. The San Juan field consists mainly of intermediate-composition lavas and breccias, erupted about 35-30 Ma from scattered central volcanoes (Conejos Formation) and overlain by voluminous ash-flow sheets erupted from caldera sources. In the central San Juan Mountains, eruption of at least 8,800 km3 of dacitic-rhyolitic magma as nine major ash flow sheets (individually 150-5,000 km3) was accompanied by recurrent caldera subsidence between 28.3 Ma and about 26.5 Ma. Voluminous andesitic-dacitic lavas and breccias were erupted from central volcanoes prior to the ash-flow eruptions, and similar lava eruptions continued within and adjacent to the calderas during the period of more silicic explosive volcanism. Exposed calderas vary in size from 10 to 75 km in maximum dimension, the largest calderas being associated with the most voluminous eruptions.

The Pagosa Springs geologic map is of the 7.5-minute quadrangle of the same name. It is located in southwestern Colorado, USA and shows the town of Pagosa Springs. The mapped area is southwest of the San Juan volcanic mountains (Oligocene) and north of the San Juan Basin. All bedrock units exposed in the map area are Upper Cretaceous in age except a minor canyon outcrop of Upper Jurassic rock. Pre-Holocene Quaternary age deposits are mainly alluvial gravels and outwash on terraces. Structure is simple: shale and sandstone beds dip at low angles east to northeast as a broad limb of the north-northwest striking Archuleta Anticline. Three geologic cross sections controlled by drill holes are included and depict Mesozoic bedrock and faults down to and including shallow Precambrian basement rock. A brief geologic history of the region is described.

The Pagosa Springs geologic map is of the 7.5-minute quadrangle of the same name. It is located in southwestern Colorado, USA and shows the town of Pagosa Springs. The mapped area is southwest of the San Juan volcanic mountains (Oligocene) and north of the San Juan Basin. All bedrock units exposed in the map area are Upper Cretaceous in age except a minor canyon outcrop of Upper Jurassic rock. Pre-Holocene Quaternary age deposits are mainly alluvial gravels and outwash on terraces. Structure is simple: shale and sandstone beds dip at low angles east to northeast as a broad limb of the north-northwest striking Archuleta Anticline. Three geologic cross sections controlled by drill holes are included and depict Mesozoic bedrock and faults down to and including shallow Precambrian basement rock. A brief geologic history of the region is described.