GEOLEX

Summary of Citation: Potosi

Publication:
Cross, C.W. and Howe, Ernest, 1905, Geography and general geology
   of the quadrangle, IN Description of the Silverton quadrangle
   [Colorado]: U.S. Geological Survey Geologic Atlas of the
   United States, Silverton folio, no. 120, 34 p.

Usage in Publication:
Potosi volcanic series*

Modifications:	Geologic Province:	Dominant Lithology:
Named	San Juan Mountain province Paradox basin	Quartz latite Rhyolite

Summary:
Named for high peak [Potosi Peak] north of Canyon Creek, San Juan Co, CO in the San Juan Mountain province. No type locality designated. Consists mostly of quartz latite and has subordinate amount of rhyolite. In northwest part of quad, Potosi is a 1,200+ ft thick unit divisible into: 1) a basal gray, coarse-grained tuff and overlying flow breccia; 2) middle gray, banded, cliff-forming flows that are separated by thin tuffs; and 3) upper red to pink, slope-forming, thin flows and tuffs. In southeast part of quad, it is composed of quartz latite and felsitic rhyolite. Unconformably overlies San Juan tuff or Silverton volcanic series. Chemical analyses. Columnar section. Mapped in southeast, northern and west-central parts of quad in San Juan and Hinsdale Cos, CO in the San Juan Mountain province and in San Miguel Co, CO in the Paradox basin. Geologic map. Tertiary age.

Summary of Citation: Potosi

Publication:
Emmons, W.H. and Larsen, E.S., 1923, Geology and ore deposits
   of the Creede district, Colorado: U.S. Geological Survey
   Bulletin, 718, 198 p.

Usage in Publication:
Potosi volcanic series*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	San Juan Mountain province

Summary:
Divided into (ascending): Alboroto and Piedra groups in the Creede district, Mineral Co, CO in the San Juan Mountain province. The oldest unit in area is the newly named Outlet Tunnel quartz latite, basal formation of Alboroto. The newly named Creede formation overlies the newly named Nelson Mountain quartz latite, upper formation of Piedra. Alboroto divided into (ascending): Outlet Tunnel quartz latite; Willow Creek and Campbell Mountain rhyolites (both named); unnamed intrusive rhyolite; Phoenix Park and Equity quartz latites (both named). Piedra divided into: 1) Mammoth Mountain rhyolite (first used); and 2) unnamed rhyolite tuff, and their equivalents the unnamed hornblende quartz latite and Windy Gulch rhyolite breccia (named); 3) unnamed tridymite latite; 4) unnamed intrusive andesite; 5) unnamed andesite; 6) unnamed quartz latite tuff; 7) Rat Creek quartz latite (named); and 8) Nelson Mountain quartz latite. Geologic map. Stratigraphic chart. Miocene age.

Summary of Citation: Potosi

Publication:
Cross, C.W. and Larsen, E.S., 1935, A brief review of the geology
   of the San Juan region of southwestern Colorado: U.S. Geological
   Survey Bulletin, 843, 138 p., Also, U.S. Geological Survey
   Professional Paper 258.

Usage in Publication:
Potosi volcanic series*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	San Juan Mountain province San Luis basin Paradox basin Piceance basin

Summary:
Erupted after a period of erosion following eruption of the Silverton volcanic series. Divided into: Conejos andesite (formerly called Conejos formation), at base; Treasure Mountain quartz latite (formerly called Treasure Mountain latite); Sheep Mountain andesite (formerly called Sheep Mountain formation); Alboroto quartz latite (formerly called Alboroto formation); Huerto andesite (formerly called Huerto formation); and Piedra rhyolite (formerly called Piedra formation). These formations are present in the San Juan Mountain province, Paradox, Piceance, and San Luis basins of CO. Is made up of alternating andesite and rhyolite latite. Thought to have covered an area of 10,000 sq mi. Has a volume of 5,600 cubic miles. Is older than Creede formation. Of Miocene age. Geologic map.

Summary of Citation: Potosi

Publication:
Luedke, R.G. and Burbank, W.S., 1963, Tertiary volcanic stratigraphy
   in the western San Juan Mountains, Colorado; Article 70, IN
   Geological Survey research 1963; short papers in geology and
   hydrology; Articles 60-121: U.S. Geological Survey Professional
   Paper, 475-C, p. C39-C44

Usage in Publication:
Potosi Volcanic Group*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	San Juan Mountain province

Summary:
Name changed from Potosi Series to Potosi Volcanic Group [in accord with Article 9f, Code of Stratigraphic Nomenclature, 1961]. Divided into Gilpin Peak Tuff (new) and Sunshine Peak Rhyolite (newly assigned to Potosi) in the San Juan Mountain province, southwest CO. Use of Gilpin Peak geographically restricts Treasure Mountain Rhyolite (or Quartz Latite). Use of Sunshine Peak geographically restricts use of Alboroto Rhyolite. Overlies Silverton Volcanic Group (name changed from Silverton Volcanic Series). Gilpin Peak is related to development of Lake City caldera. Assigned a middle and late Tertiary age.

Summary of Citation: Potosi

Publication:
Steven, T.A. and Ratte, J.C., 1964, Revised Tertiary volcanic
   sequence in the central San Juan Mountains, Colorado; Article
   132, IN Geological Survey research 1963; short papers in
   geology and hydrology; Articles 122-170: U.S. Geological
   Survey Professional Paper, 475-D, p. D54-D63

Usage in Publication:
Potosi Volcanic Series

Modifications:	Geologic Province:	Dominant Lithology:
Not used

Summary:
Not used in Creede area, Mineral Co, CO, San Juan Mountain province. Not able to accommodate to the revised volcanic sequence as determined by authors in this report.

Summary of Citation: Potosi

Publication:
Olson, J.C., Hedlund, D.C. and Hansen, W.R., 1968, Tertiary
   volcanic stratigraphy in the Powderhorn-Black Canyon region,
   Gunnison and Montrose Counties, Colorado, IN Contributions
   to general geology, 1967: U.S. Geological Survey Bulletin,
   1251-C, p. C1-C29

Usage in Publication:
Potosi Volcanic Series*

Modifications:	Geologic Province:	Dominant Lithology:
Not used

Summary:
Ash-flow tuffs of Tertiary age formerly assigned to Potosi Volcanic Series in Montrose Co, CO in Paradox basin and in Gunnison Co, CO in Piceance basin reassigned to five new formations. Blue Mesa (base), Dillon Mesa, and Sapinero Mesa Tuffs replace the lower member of Alboroto. Fish Canyon Tuff replaces upper member of Alboroto. Carpenter Ridge Tuff replaces Piedra Rhyolite. Alboroto, Piedra, and Potosi not abandoned; they are not used.

Summary of Citation: Potosi

Publication:
Luedke, R.G., 1972, Geologic map of the Wetterhorn Peak quadrangle,
   Colorado: U.S. Geological Survey Geologic Quadrangle Map,
   GQ-1011, 1 sheet, scale 1:24,000

Usage in Publication:
Potosi Volcanic Group*

Modifications:	Geologic Province:	Dominant Lithology:
Mapped 1:24k (Hinsdale and Ouray Cos, CO)	San Juan Mountain province	Tuff Quartz latite

Summary:
Is Oligocene volcanic group mapped as a single map unit in scattered areas throughout quadrangle in southeast Ouray and western Hinsdale Cos, CO (San Juan Mountain province). Overlies Henson Formation of Oligocene Silverton Volcanic Group; is youngest formal bedrock unit mapped in the quadrangle. Map unit described as light-gray to grayish-brown predominantly devitrified quartz latite welded ash-flow tuffs; moderately crystal rich with biotite, pyroxene, feldspar, and quartz most common in a eutaxitic and vitroclastic matrix; vertically columnar jointed; locally absent in map area owing in part to nondeposition and in part to erosion. [Thickness is not given; appears to be as thick as 1,120 ft based on map expression.]

Summary of Citation: Potosi

Publication:
Lipman, P.W., Steven, T.A., Luedke, R.G. and Burbank, W.S.,
   1973, Revised volcanic history of the San Juan, Uncompahgre,
   Silverton, and Lake City calderas in the western San Juan
   Mountains, Colorado: U.S. Geological Survey Journal of
   Research, v. 1, no. 6, p. 627-642

Usage in Publication:
Potosi Volcanic Group*

Modifications:	Geologic Province:	Dominant Lithology:
Abandoned

Summary:
Abandoned as a rock-stratigraphic unit in the San Juan volcanic field, San Juan Mountain province, CO. As redefined by Burbank and Luedke (1963), Potosi consisted of Gilpin Peak Tuff (base) and Sunshine Peak Rhyolite (top). Gilpin Peak consists of four ash-flow sheets, known as the Ute Ridge, Blue Mesa, Dillon Mesa, and Sapinero Mesa Tuffs; these four tuffs were derived from four unrelated calderas. The name Gilpin Peak is abandoned. The Sunshine Peak is known to overlie Potosi and to be younger than Henson Formation.