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 dataset is intended to provide seamless, integrated, surficial geologic mapping of the U.S. Intermountain West region and is supported by the National Cooperative Geologic Mapping Program of the U.S. Geological Survey. Surficial geology included as part of this data release as independent of bedrock geologic mapping and is compiled at a variable resolution from 1:50,000 to 1:250,000 scale. No original interpretations are presented in this dataset; rather, all interpretive data are assimilated from referenceable publications. Initial contributions to this data release are along an east-west transect that parallels 37-degrees north latitude extending from the Rio Grande Rift and Great Plains in the east to the Basin and Range and Sierra Nevada to the west. Other areas of the Intermountain West region will be incorporated over time. Data are presented as a downloadable file geodatabase (*.gdb) and as features services that can be directly ingested into GIS software for analysis. This dataset is intended to be versioned regularly as new geologic map data is integrated. The data structure follows the Seamless Integrated Geologic Mapping extension (SIGMa) (Turner and others, 2022) to the Geologic Map Schema (GeMS) (USGS, 2020). U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10. Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/10.3133/ sir20225115.

This dataset is intended to provide seamless, integrated geologic mapping of the U.S. Intermountain West region as a contribution to The National Geologic Map supported by the National Cooperative Geologic Mapping Program of the U.S. Geological Survey. Surficial and bedrock geology are included in this data release as independent datasets at a variable resolution from 1:50,000 to 1:250,000 scale. No original interpretations are presented in this dataset; rather, all interpretive data are assimilated from referenceable publications. Derivative polygon features created for this dataset demonstrate the distribution of SIGMa-GeMS Geologic Provinces derived from the distribution of map units. Initial contributions to this data release are along an east-west transect along 37-degrees north latitude that extends from the Rio Grande Rift and Great Plains in the east to the Basin and Range and Sierra Nevada to the west. Other areas of the Intermountain West region will be incorporated over time. Data are presented as downloadable file geodatabases (*.gdb) and as features services that can be directly ingested into GIS software for analysis. This dataset is intended to be versioned regularly as new geologic map data is integrated. The data structure follows the Seamless Integrated Geologic Mapping extension (SIGMa) (Turner and others, 2022) to the Geologic Map Schema (GeMS) (USGS, 2020). U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10. Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/10.3133/ sir20225115.

This dataset is intended to provide seamless, integrated, surficial geologic mapping of the U.S. Intermountain West region and is supported by the National Cooperative Geologic Mapping Program of the U.S. Geological Survey. Surficial geology included as part of this data release as independent of bedrock geologic mapping and is compiled at a variable resolution from 1:50,000 to 1:250,000 scale. No original interpretations are presented in this dataset; rather, all interpretive data are assimilated from referenceable publications. Initial contributions to this data release are along an east-west transect that parallels 37-degrees north latitude extending from the Rio Grande Rift and Great Plains in the east to the Basin and Range and Sierra Nevada to the west. Other areas of the Intermountain West region will be incorporated over time. Data are presented as a downloadable file geodatabase (*.gdb) and as features services that can be directly ingested into GIS software for analysis. This dataset is intended to be versioned regularly as new geologic map data is integrated. The data structure follows the Seamless Integrated Geologic Mapping extension (SIGMa) (Turner and others, 2022) to the Geologic Map Schema (GeMS) (USGS, 2020). U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10. Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/10.3133/ sir20225115.

The San Juan Mountains in southwestern Colorado have long been recognized as a site of exceptionally voluminous mid-Tertiary volcanism, including at least 24 major ignimbrite sheets (each 150-5,000 km3) and associated caldera structures active at 33-23 Ma. More recent volcanologic and petrologic studies in the San Juan region have focused mainly on several ignimbrite-caldera systems: the southeastern area (Platoro complex), western calderas (Uncompahgre-Silverton-Lake City), the central cluster (La Garita-Creede calderas). The northeast San Juan region that was far less studied until recently occupies a transition between earlier volcanism in central Colorado and the larger-volume younger ignimbrite-caldera foci farther south and west. The present study of the Bonanza area evaluates eruptive and magmatic processes of silicic Cordilleran volcanism in this northeast region, based on new geologic mapping (mainly summers of 2007-12) and concurrent petrologic and geochronologic analysis. The resulting map is based on new field mapping of volcanic rocks in thirteen 7.5-minute quadrangles in northeastern parts of the volcanic field, petrologic studies involving several hundred new chemical analyses, and high-resolution age determinations for about 130 sites. The Bonanza center contains exceptionally complete and diverse features of an ignimbrite caldera cycle, including voluminous andesite erupted before and after ignimbrite eruptions, complex compositional zonation within both the outflow ignimbrite sheet and the tuff concurrently ponded within the caldera, extensive portions of the ring-fault system that accommodated subsidence, thick compositionally diverse lavas that filled the caldera after subsidence, remnants of the original topographic caldera rim, widespread erosional exposure of caldera-floor features, and postcaldera granitic intrusions that generated a notably steep resurgent dome within the caldera.

The San Juan Mountains in southwestern Colorado have long been recognized as a site of exceptionally voluminous mid-Tertiary volcanism, including at least 24 major ignimbrite sheets (each 150-5,000 km3) and associated caldera structures active at 33-23 Ma. More recent volcanologic and petrologic studies in the San Juan region have focused mainly on several ignimbrite-caldera systems: the southeastern area (Platoro complex), western calderas (Uncompahgre-Silverton-Lake City), the central cluster (La Garita-Creede calderas). The northeast San Juan region that was far less studied until recently occupies a transition between earlier volcanism in central Colorado and the larger-volume younger ignimbrite-caldera foci farther south and west. The present study of the Bonanza area evaluates eruptive and magmatic processes of silicic Cordilleran volcanism in this northeast region, based on new geologic mapping (mainly summers of 2007-12) and concurrent petrologic and geochronologic analysis. The resulting map is based on new field mapping of volcanic rocks in thirteen 7.5-minute quadrangles in northeastern parts of the volcanic field, petrologic studies involving several hundred new chemical analyses, and high-resolution age determinations for about 130 sites. The Bonanza center contains exceptionally complete and diverse features of an ignimbrite caldera cycle, including voluminous andesite erupted before and after ignimbrite eruptions, complex compositional zonation within both the outflow ignimbrite sheet and the tuff concurrently ponded within the caldera, extensive portions of the ring-fault system that accommodated subsidence, thick compositionally diverse lavas that filled the caldera after subsidence, remnants of the original topographic caldera rim, widespread erosional exposure of caldera-floor features, and postcaldera granitic intrusions that generated a notably steep resurgent dome within the caldera.

This dataset is intended to provide seamless, integrated bedrock geologic mapping of the U.S. Intermountain West region and is funded by the National Cooperative Geologic Mapping Program of the U.S. Geological Survey. Bedrock geology are included in this data release as an independent dataset at a variable resolution from 1:50,000 to 1:100,000 scale. No original interpretations are presented in this data set; rather, all interpretive data are assimilated from referenceable publications. Initial contributions to this data release are along an east-west transect that parallels 37-degrees north latitude extending from the Rio Grande Rift and Great Plains in the east to the Basin and Range and Sierra Nevada to the west. Other areas of the Intermountain West region will be incorporated over time. Data are presented as downloadable file geodatabase (*.gdb) and as features services that can be directly ingested into GIS software for analysis. This dataset is intended to be versioned regularly as new geologic map data is integrated. The data structure follows the Seamless Integrated Geologic Mapping extension (SIGMa) (Turner and others, 2022) to the Geologic Map Schema (GeMS) (USGS, 2020). U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10. Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/10.3133/ sir20225115.

This dataset is intended to provide seamless, integrated bedrock geologic mapping of the U.S. Intermountain West region and is funded by the National Cooperative Geologic Mapping Program of the U.S. Geological Survey. Bedrock geology are included in this data release as an independent dataset at a variable resolution from 1:50,000 to 1:100,000 scale. No original interpretations are presented in this data set; rather, all interpretive data are assimilated from referenceable publications. Initial contributions to this data release are along an east-west transect that parallels 37-degrees north latitude extending from the Rio Grande Rift and Great Plains in the east to the Basin and Range and Sierra Nevada to the west. Other areas of the Intermountain West region will be incorporated over time. Data are presented as downloadable file geodatabase (*.gdb) and as features services that can be directly ingested into GIS software for analysis. This dataset is intended to be versioned regularly as new geologic map data is integrated. The data structure follows the Seamless Integrated Geologic Mapping extension (SIGMa) (Turner and others, 2022) to the Geologic Map Schema (GeMS) (USGS, 2020). U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10. Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/10.3133/ sir20225115.

The dataset includes whole-rock geochemistry and 40Ar-39Ar geochronology for Pleistocene to Oligocene volcanic and intrusive rocks. These data support figures and tables in days 2 and 3 of the Field-trip guide to continental arc to rift volcanism of the southern Rocky Mountains-Southern Rocky Mountain, Taos Plateau, and Jemez Mountains volcanic fields of southern Colorado and northern New Mexico (Thompson and others, 2022). Additional 40Ar-39Ar geochronology data are included for age reported in the Geologic map of Ute Mountain quadrangle (Thompson and others, 2014b) and the Geologic map of Sunshine quadrangle (Thompson and others, 2014a). Other samples not associated with any of these referenced publications are also included. > There may be slight variation in the ages reported here and other previously reported ages on the geologic maps for the Sunshine and Ute Mountain quadrangles (Thompson and others 2014a,b) and some ages originally reported on the Geologic map of the San Antonio Mountain area (Turner and others, 2017) due to statistical methods used in calculating the age.

The dataset includes whole-rock geochemistry and 40Ar-39Ar geochronology for Pleistocene to Oligocene volcanic and intrusive rocks. These data support figures and tables in days 2 and 3 of the Field-trip guide to continental arc to rift volcanism of the southern Rocky Mountains-Southern Rocky Mountain, Taos Plateau, and Jemez Mountains volcanic fields of southern Colorado and northern New Mexico (Thompson and others, 2022). Additional 40Ar-39Ar geochronology data are included for age reported in the Geologic map of Ute Mountain quadrangle (Thompson and others, 2014b) and the Geologic map of Sunshine quadrangle (Thompson and others, 2014a). Other samples not associated with any of these referenced publications are also included. > There may be slight variation in the ages reported here and other previously reported ages on the geologic maps for the Sunshine and Ute Mountain quadrangles (Thompson and others 2014a,b) and some ages originally reported on the Geologic map of the San Antonio Mountain area (Turner and others, 2017) due to statistical methods used in calculating the age.