Geologic units in Saguache county, Colorado

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 29 % of this area

Includes several named units

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Quaternary-Tertiary) at surface, covers 21 % of this area

Alamosa Fm: gravel, sand, silt

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 18 % of this area

Includes many named units

Gravels and alluviums (Quaternary) at surface, covers 7 % of this area

Includes Broadway and Louviers Alluviums

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 5 % of this area

Includes metabasalt, metatuff, and interbedded metagraywacke; locally contains interlayered biotite gneiss. Derived principally from volcanic rocks

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 3 % of this area

Includes Boulder Creek -M.Y. AGE GROUP (AGE 1650-1730 M.Y.)--Includes Boulder Creek, Cross Creek, Denny Creek, Kroenke, Browns Pass, Powderhorn, Pitts Meadow, Bakers Bridge, and Tenmile Granites, Quartz Monzonites, or Granodiorites; also, unnamed granitic rocks

Eolian deposits (Quaternary) at surface, covers 3 % of this area

Includes dune sand and silt and Peoria Loess

Landslide deposits (Quaternary) at surface, covers 2 % of this area

Locally includes talus, rock-glacier, and thick colluvial deposits

Sangre de Cristo Fm (Permian-Pennsylvanian) at surface, covers 2 % of this area

Arkosic conglomerate, sandstone, and siltstone

Minturn and Belden Fms (Pennsylvanian) at surface, covers 2 % of this area

Minturn and Belden Fms

Modern alluvium (Quaternary) at surface, covers 1 % of this area

Includes Piney Creek Alluvium and younger deposits

Intra-ash flow andesitic lavas (Tertiary) at surface, covers 1 % of this area

Intra-ash flow andesitic lavas

Intra-ash flow quartz latitic lavas (Tertiary) at surface, covers 1.0 % of this area

Intra-ash flow quartz latitic lavas

Dakota, Burro Canyon, Morrison, and Junction Creek Fms (Cretaceous-Jurassic) at surface, covers 0.8 % of this area

Burro Canyon is locally absent

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 0.7 % of this area

Locally contains minor hornblende gneiss, calc-silicate rock, quartzite, and marble. Derived principally from sedimentary rocks

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.6 % of this area

Intermediate to felsic compositions

Mancos Shale (Cretaceous) at surface, covers 0.6 % of this area

In northwest and west-central: Intertongues complexly with units of overlying Mesaverde Group or Fm; lower part consists of a calcareous Niobrara equivalent and Frontier Sandstone and Mowry Shale Members; in areas where the Frontier and Mowry Members (Kmfm), or these and the Dakota Sandstone (Kfd) are distinguished, map unit (Km) consists of shale above Frontier Member. In Southwest: Lower part contains Juana Lopez Member (Kmj)

Glacial drift (Quaternary) at surface, covers 0.5 % of this area

Includes some unclassified glacial deposits

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone (Mississippian-Ordovician) at surface, covers 0.5 % of this area

Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone

Morrison Fm and Junction Creek Sandstone (Jurassic) at surface, covers 0.4 % of this area

In Gunnison River area east of wedgeout of all units of Wanakah Fm (Jmw) except the Junction Creek Member

Older gravels and alluviums (Quaternary) at surface, covers 0.4 % of this area

Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers 0.3 % of this area

Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences

Dakota Sandstone or Group (Cretaceous) at surface, covers 0.2 % of this area

Dakota Sandstone or Group

Dry Union Fm (Tertiary) at surface, covers 0.2 % of this area

Siltstone, sandstone, and conglomerate. Includes Wagontongue Fm (Miocene) in South Park

Mafic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.1 % of this area

Gabbro and mafic diorite and monzonite

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 0.1 % of this area

Includes Silver Plume, Sherman, Cripple Creek, St. Kevin, Vernal Mesa, Curecanti, Eolus, and Trimble Granites or Quartz Monzonites; also, San Isabel Granite of Boyer (1962) and unnamed granitic rocks

Parting, Fremont, and Harding Fms (Devonian-Ordivician) at surface, covers < 0.1 % of this area

Parting, Fremont, and Harding Fms

Santa Fe Fm (Tertiary) at surface, covers < 0.1 % of this area

Siltstone, sandstone, and conglomerate

Oligocene sedimentary rocks (Tertiary) at surface, covers < 0.1 % of this area

Northwest: includes Duchesne River Fm (sandstone and shale; includes some rocks of Eocene age) and Bishop Conglomerate near Utah border. South-central: includes Florissant Lake Beds (tuffaceous shale and tuff) and Antero Fm (limestone tuff, tuffaceous sandstone, and conglomerate). Southwest: includes Creede Fm (tuffaceous siltstone, sandstone, conglomerate) and gravels interbedded with volcanic rocks northeast and southeast of Gunnison

Dakota and Morrison Fms (Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

Dakota and Morrison Fms

One or more Ordovician fms (Ordovician) at surface, covers < 0.1 % of this area

Fremont Limestone, Harding Sandstone, and Manitou Limestone

Minturn Fm in west-central and south-central and other units (Pennsylvanian) at surface, covers < 0.1 % of this area

Arkosic sandstone, conglomerate, shale, and limestone. Includes Madera Fm and Sharpsdale Fm of Chronic (1958) in Sangre de Cristo Range and Gothic Fm of Langenheim (1952) in Elk Mountains. Other units of Middle Pennsylvanian age.