Cimarron Ridge

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.


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).


Post a Comment