- Usage in publication:
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- Bakers Bridge Granite*
- Modifications:
-
- Original reference
- Dominant lithology:
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- Granite
- AAPG geologic province:
-
- Southern Rocky Mountain region
Summary:
Pg. A6-A7 (map), A23-A24. Bakers Bridge Granite. Stock of massive, pale-red, medium- to coarse-grained granite and alaskite. Composed chiefly of perthite and quartz with less than 10 percent plagioclase and dark minerals. Accessory minerals are allanite and fluorite. Exposed for about 3 square miles in the Rockwood-Shalona Lake-Bakers Bridge area, La Plata Co., southwestern CO. In southeastern part of area, includes a cross-cutting quartz monzonite that may not be cogenetic. Younger than Twilight Gneiss; older than Uncompahgre Formation; age-equivalent of Tenmile Granite. Age is considered Precambrian X. U-Pb age of 1,720 +/-20 Ma (zircons) reported by Silver and Barker [abs.], 1968, GSA Spec. Paper 115, p. 204-205; Rb-Sr age of 1,692 +/-78 Ma (whole-rock) reported by Bickford and others [abs.], 1968, GSA Spec. Paper 115, p. 14.
Type locality: Bakers Bridge, which spans Animas River 24.1 km northwest of Durango, [Lat. 37 deg. 27 min. 32 sec. N., Long. 107 deg. 47 min. 57 sec. W.], Hermosa 7.5-min quadrangle, La Plata Co., southwestern CO.
[Misprint (US geologic names lexicon, USGS Bull. 1520, p. 16): original reference should be USGS Prof. Paper 644-A, not USGS Bull. 1272-F.]
Source: Publication; US geologic names lexicon (USGS Bull. 1520, p. 16); GNU records (USGS DDS-6; Denver GNULEX).
- Usage in publication:
-
- Bakers Bridge Granite*
- Modifications:
-
- Areal extent
- AAPG geologic province:
-
- Southern Rocky Mountain region
Summary:
Pg. D2 (fig. 1), D6 (table 1). Bakers Bridge Granite. Exposed only in one stock in Needle Mountains, [La Plata County], southwestern Colorado. Age is considered Precambrian X (Bickford and others, 1969, Jour. Geophys. Research, v. 74, no. 6, p. 1660-1676, report an age of 1711 +/-80 Ma).
Source: Publication.
- Usage in publication:
-
- Bakers Bridge Granite*
- Modifications:
-
- Revised
- AAPG geologic province:
-
- Southern Rocky Mountain region
Summary:
Bakers Bridge Granite of Routt Plutonic Suite (new name). Pale-red, coarse-grained, massive, homogeneous granite. Consists largely of microcline perthite and quartz, and small amounts of plagioclase and biotite. Exposed in one stock in Needle Mountains, and is partially exposed 22 km (14 miles) north of Durango, [La Plata County], Animas River Valley, southwestern Colorado. Age is Early Proterozoic (U-Pb age of 1,695 +/-20 Ma and Rb-Sr age of 1,658 +/-78 Ma).
Source: Modified from GNU records (USGS DDS-6; Denver GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).