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Radial Dikes of the San Luis Valley - the Summer Coon Volcano 
This image illustrates what the Summer Coon Volcano may have looked
like 32 million years ago. Image: V. Matthews
North of the town of Del Norte, Colorado are exposures which provide the opportunity to observe the insides of a stratovolcano about the size of Mount Shasta in California.

The original extent of the volcano was 12 to 15 miles across, with a central intrusive complex in the throat of the volcano.  The stratovolcano has been mostly eroded away and all that is left are the radiating dikes and central plug that are the roots of the volcano.

Radiating out from the central intrusives are hundreds of dikes of varying composition; ten of the larger ones can be identified from the aerial photograph below(red arrows).

Aerial photograph of the Summer Coon radial dike swarm. Red arrows point to the more prominent dikes. Click image to enlarge.

Geologic Map of the Summer Coon radial dike swarm.
Click image to enlarge.


On-the-ground view of one of the northern rhyolitic dikes of the Summer Coon Volcano.

Simplified Geologic map of the Summer Coon Volcano showing typical pattern of radial dike swarm with central core.  Click image to enlarge.

R.P. Smith, Dyke emplacement at Spanish Peaks, Colorado, in: H.C. Halls, W.F. Fahrig (Eds.), Map of Dyke Swarms, Geol. Soc. Can. Spec. Pap. 34 (1987) pp. 47-54.
31 (1988) pp. 65-75.

W.P. Moats, Geometry and Emplacement of Silicic Dikes at Summer Coon Volcano, Rio Grande and Saguache Counties, Colorado, M.S. Thesis, Arizona State University, Tempe, AZ, 1990, unpublished.

P.W. Lipman, T.A. Steven, L.H. Mehnert, Volcanic history of the San Juan mountains, Colorado, as indicated
by potassium-argon dating, Geol. Soc. Am. Bull. 81 (1970) pp. 2329-2352.

F.V. Perry, G. Woldegabriel, G.A. Valentine, E.K. Desmaraus, G. Heiken, M. Heizler, M. Yamakawa, K. Ume-168., M.P. Poland et al. /Earth and Planetary Science Letters 219 (2004) pp. 155-169 da, High-level radioactive waste disposal and volcanic hazard in Japan: A natural analog study of Summer Coon volcano, Colorado, Geol. Soc. Am. Abstr. Programs 31 (1999) A478.

P.W. Lipman, Geology of the Summer Coon volcanic center, eastern San Juan Mountains, Colorado, Colorado Sch. Mines Q.63 (1968) pp. 211-236.

S.A. Mertzman, The Summer Coon volcano, eastern San Juan mountains, Colorado, in: H.L. James (Ed.), San Luis Basin Guidebook, New Mexico Geological Society,
Socorro, NM, 1971, pp. 265-272.

Last Updated: 10/29/2012 10:33 AM 
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