Geologic units in Archuleta county, Colorado

Additional scientific data in this geographic area

Pictured Cliffs Sandstone and Lewis Shale (Cretaceous) at surface, covers 14 % of this area

Pictured Cliffs Sandstone and Lewis Shale

Mancos Shale (Cretaceous) at surface, covers 14 % 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)

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 14 % of this area

Includes several named units

Animas Fm (Tertiary-Cretaceous) at surface, covers 11 % of this area

Arkosic sandstone, shale, and conglomerate; contains abundant volcanic materials; Upper Cretaceous volcaniclastic McDermott Member at base

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 9 % of this area

Sandstone, shale, and conglomerate. In northwest and west-central: Lower Cretaceous. In southwest: Lower and Upper Cretaceous.

San Jose Fm (Tertiary) at surface, covers 8 % of this area

Siltstone, shale, and sandstone

Mesaverde Fm, undivided (Cretaceous) at surface, covers 8 % of this area

In northwest and west-central: Major coal beds in lower part; Rollins Sandstone Member at base in Delta, Gunnison, and Pitkin Counties. In southwest: sandstone and shale.

Landslide deposits (Quaternary) at surface, covers 6 % of this area

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

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 4 % of this area

Morrison, Wanakah, and Entrada Fms

Modern alluvium (Quaternary) at surface, covers 4 % of this area

Includes Piney Creek Alluvium and younger deposits

Kirtland Shale and Fruitland Fm (Cretaceous) at surface, covers 2 % of this area

Shale, sandstone, and major coal beds

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 1 % of this area

Intermediate to felsic compositions

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 1 % of this area

Includes many named units

Rico and Hermosa Fms (Pennsylvanian) at surface, covers 0.9 % of this area

Arkosic sandstone, conglomerate, shale, and limestone. Includes at base in some areas siltstone and shale of Molas Fm or Larsen Quartzite

Cutler Fm (Permian) at surface, covers 0.9 % of this area

Arkosic sandstone, siltstone, and conglomerate

Eocene prevolcanic sedimentary rocks (Tertiary) at surface, covers 0.9 % of this area

South-central: Arkosic sand and bouldery gravel of Echo Park Alluvium. Southwest: includes Telluride Conglomerate and Blanco Basin Fm (arkosic mudstone, sandstone, and conglomerate)

Dolores Fm (Triassic) at surface, covers 0.6 % of this area

Red siltstone, shale, sandstone, and limestone-pellet conglomerate

Older gravels and alluviums (Quaternary) at surface, covers 0.3 % of this area

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

Older glacial drift (Quaternary) at surface, covers 0.3 % of this area

Older glacial drift

Glacial drift (Quaternary) at surface, covers 0.1 % of this area

Includes some unclassified glacial deposits

Animas Formation (Paleocene and upper Cretaceous) at surface, covers < 0.1 % of this area

Volcaniclastic sedimentary rocks of intermediate composition in northern San Juan Basin.

San Jose Formation (Eocene) at surface, covers < 0.1 % of this area

San Juan Basin

Morrison Fm and Wanakah Fm (Junction Creek Sandstone Member at or near top; Pony Express Limestone Member at base) (Jurassic) at surface, covers < 0.1 % of this area

Wanakah Fm: Sandstone, shale, limestone, and local gypsum

Intra-ash flow andesitic lavas (Tertiary) at surface, covers < 0.1 % of this area

Intra-ash flow andesitic lavas

Uncompahgre Fm (Early-Middle Proterozoic) at surface, covers < 0.1 % of this area

Quartzite, slate, and phyllite

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers < 0.1 % of this area

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

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

Mesaverde Group (Campanian to Turonian) at surface, covers < 0.1 % of this area

Includes Cliff House Sandstone, Menefee Formation, and Point Lookout Sandstone.

Lewis Shale (Campanian) at surface, covers < 0.1 % of this area

Marine shale and mudstone.

Landslide deposits and colluvium (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

Landslide deposits on western flanks of Socorro Mountains not shown for clarity.

Mancos Shale (Cenomanian to Campanian) at surface, covers < 0.1 % of this area

Divided into Upper and Lower parts by Gallup Sandstone.

Tertiary mafic intrusive rocks (Pliocene to upper Eocene) at surface, covers < 0.1 % of this area

Includes many long basaltic andesite dikes of Oligocene age near Pie Town, Acoma, Riley, Chupadera, Truth or Consequences, Roswell, Raton, and Dulce; and several elongate or shoestring-like sills of basalt or basaltic andesite. Also includes basaltic necks of Pliocene age that dot the landscape northeast of Mount Taylor. Where dikes extend into Quaternary alluvium the contact is an unconformity.

Lower middle Tertiary volcanic rocks (Lower Oligocene to upper Eocene (older than 31 Ma)) at surface, covers < 0.1 % of this area

Mostly intermediate lavas of the lower Datil Group and intermediate volcaniclastic sediments of the lower Spears Group (Tla+Tvs). Locally includes ash-flow tuffs of the upper Datil Group (Tlrp). Includes intermediate volcaniclastic sedimentary rocks of the Conejos Formation in northern New Mexico.

Piedmont alluvial deposits (Holocene to lower Pleistocene) at surface, covers < 0.1 % of this area

Includes deposits of higher gradient tributaries bordering major stream valleys, alluvial veneers of the piedmont slope, and alluvial fans. May locally include uppermost Pliocene deposits.

Paleogene sedimentary units (Paleogene) at surface, covers < 0.1 % of this area

Includes Baca, Galisteo, El Rito, Blanco Basin, Hart Mine, Love Ranch, Lobo, Sanders Canyon, Skunk Ranch, Timberlake, and Cub Mountain Formations.

Pictured Cliffs Sandstone (Campanian) at surface, covers < 0.1 % of this area

Prominent cliff-forming marine sandstone.

Kirtland and Fruitland Formations (Campanian) at surface, covers < 0.1 % of this area

Coal-bearing, primarily in the Fruitland.