From the Hall of Disjointed Memories, Part 29: First Look at the San Juans | Southwestern Colorado, USA

The one thing that's certain here is that I took this shot while sticking my head out the passenger-side window of a Chevy Suburban. Exact location: unknown. Direction I'm facing: unknown. What I do recall is that this is the first of three scenes showing the San Juan Mountains. If you know where this locale is, please enlighten me.

Also, note that the position I've put on the geotagging map is very approximate.

One of the main objectives of our circum-Colorado field-course trip was mining localities in the San Juans. As noted in Part 28, economic geology was the great idée fixe of our professors.

At first I was tempted to crop this photo to remove as much of the peripheral blur as possible, but I could not bring myself to cut out a major portion of that lovely cumulus-congestus cloudscape.

I've had the bad habit, which first surfaced in childhood, of taking pictures of mountain ranges and other notable objects the very first time I see them, even if they are barely perceptible. (This shot of the Parthenon, taken one summer previous, is another example of that syndrome.) But I'm pretty sure I was so excited to see the San Juans here I couldn't resist pulling out my trusty Instamatic.

In any event, this image and its companions have inspired me to revisit the geology of the places they show.

It seems remarkable to me now how much geology has changed since I snapped this. At that point the theory of plate tectonics, still in its infancy, had not reached the consciousness or lesson plans of my university instructors. Half a century later, I can wade through an ample literature tying the formation of the San Juans to the magma-generating propensity of the Farallon Plate subducting under western North America.

So at long last I know this. While they seem to be just another picture-postcard-beautiful mountain range in Colorado, the San Juans have a particularly interesting—and violent—origin story. They began as a large cluster of stratovolcanoes that formed in the Oligocene epoch. Eventually almost a score of calderas developed in this volcanic field, including the one produced by the La Garita Supervolcano in one of the most powerful and extensive eruptions recorded in Earth history.

Volcanic activity continued into the Miocene and Pliocene, but the event that probably did much to thrust the range into its present lofty position was the advent of the Rio Grande Rift.

The rift was in turn one particularly dramatic expression of the Basin and Range lithospheric extension that began in this part of the West in the Miocene. As the crust stretched, a succession of uplifted areas (such as these mountains) alternated with down-dropped sections. That said, I should note that the San Juans lie not in the officially designated Basin and Range physiographic province, but in the Southern Rocky Mountains province instead.

In this region there are also imprints of the earlier, compressional phase known as the Laramide Orogeny. For instance, the adjoining San Juan Basin to the south is a structural feature produced during that time, in the late Cretaceous and early Tertiary.

You'll find the other photos and descriptions of this series in my From the Hall of Disjointed Memories album.

Taken in: United States / Colorado / Beartown (historical) (show map)

Taken on: July 1, 1974

Tags:

geology

landscape

Colorado

San Juan Mountains

mountains

mountain range « less

Sets appears in: • From the Hall of Disjointed Memories • Mountains & Hills; Mesas & Buttes; Hogbacks, Cuestas, & Flatirons more » • Natural History: Colorado • Ortsinn: Landscapes & Localities « less

Groups appears in: • Landschaft/Landscape • Rocks and Geology more » • Geology Rockers • Mountains • GeoTagging Flickr • Geotagged • Geology • Colorado Scenery • Geologists • Mountain Scenes • Mountains, Mountains just Mountains... • Mountains Anywhere • USA - UNITED STATES OF AMERICA • nature and landscape photography • North American Nature & Wildlife Photography • Landscapes of the World • Geotagged: Colorado • Geology for all • Geology/EarthScience • Structural Geology • Colorado Landscape & Wildlife Photos • America's Best Landscapes • Mountains in the world • American Photography • Colorado Photography Pool • Nature Photography // • Geology Flickrs • USA Landscape Photography • Colorado Nature Photographers • Nature Album • Landscape Photography: From Snapshots to Great Shots • Landscapes of the earth • On Landscape • Landscapes Only • Photography with a Story • Geology / Geologie • Nature and all that is beautiful • The Very Great Outdoors • We love Nature and Geology • American West Flickrology « less

Camera: MAKER NAME 96660, f/1.8, 1/173 sec, 2.8mm, ISO 50 (more info) (hide info)

Camera:	MAKER NAME 96660
Aperture:	f/1.8
Exposure Time:	0.006 sec (1/173)
Focal Length:	2.8mm
ISO:	50
Exposure Bias:	-0.7 EV
Flash:	Auto, Did not fire
Exposure Program:	Program AE
Metering Mode:	Average
White Balance:	Auto
Color Space:	Uncalibrated
Software:	Inpaint
Show full info

Stats: 245 views

go back