Cimarron Ridge is a ridge in southern Colorado's San Juan Mountains. The ridge stretches north to south across Gunnison,
Montrose, Ouray, and Hinsdale counties. The ridge runs parallel to US Roadway
550, and parts of it can be seen from the highway. The green and grey tuff
breccia ridge are the "erosional remains of a bigger volcanic pile that
encompassed multiple volcanoes." The ridge gives its name to the Cimarron
Ridge Formation. The elevation is 3710m.
Summary:
Cimarron
Ridge, on the border of Ouray (San Juan Mountain province) and Gunnison
(Paradox basin) counties in Colorado, is named after characteristic exposures.
The remains of a larger volcanic pile that ringed multiple volcanoes in the
Ouray area south and east of Spruce Ridge have been eroded. The majority of the
pile was eroded by early Tertiary erosion. Under younger volcanic, it appears
to spread eastward. Is made up of interbedded air-fall and lauric tuff breccia,
as well as a volcanic-derived conglomerate, sandstone, and mudstone with
thicknesses ranging from 0-600 feet. To the south, the tuff breccia is predominantly
green and grey, with the occasional flow and flow breccia.
In an aphanitic groundmass, the volcanic pieces
are predominantly coarsely porphyritic rhyodacite with phenocrysts of zoned
plagioclase, brown biotite, pyroxene, quartz, and little apatite. Mancos Shale,
Fruitland Formation, and Kirtland Shale are all unconformably overlain.
Telluride Conglomerate and San Juan Formation are
unconformably overlain. Based on pollen and spores, as well as K-Ar age
determinations on rhyodacite of 70.1 +/-2.1 million years for biotite, 61.5
+/-6.2 million years for plagioclase, and 86.9 +/-4.3 million years for
hornblende.
Source:
GNU records (USGS DDS-6; Denver GNULEX).
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