Wednesday, October 31, 2007

GSA: getting there is half the fun

I live a seven-hour drive from Denver. There's an airport near me, but the flights are expensive and frequently delayed or cancelled, so when I have to go to Denver, I drive.

A seven-hour drive can be rough... unless it looks like this:

My drive takes me up into the headwaters of the San Juan River, over the continental divide, and into the headwaters of the Rio Grande, Arkansas River, and South Platte River. People go out of their way to vacation in the places that I have to drive through to get to Denver.

The photo is of the northern Sangre de Cristo mountains, on the eastern side of the Rio Grande Rift. The peaks are Precambrian igneous and metamorphic rocks, sillimanite grade and partially melted - I did my senior thesis research in the area. Further to the south, the Precambrian is covered by layers of sedimentary rock, all tilted towards the east, away from the fault. The range front is a normal fault, possibly still active. The valley is filled with sediments: lots of alluvial fan gravels, interbedded with lake sediments from wetter times. The western side of the valley is much less dramatic: hills of Tertiary volcanic rocks from the San Juan field are partially buried by the young gravels. Streams in the area feed an artesian groundwater system - as I drove across yesterday, I could see crusts of white minerals on the soil, left behind from evaporation of standing water. The Great Sand Dunes National Park is along the range front - the sand is carried into the valley by streams, and then blown back along the valley by the prevailing west winds. It's a particularly beautiful example of a half graben.

There was a session (that I missed, unfortunately) on groundwater and tectonics of the Rio Grande Rift. It focused more on the Albuquerque area (for good reason: there are a lot of people using that groundwater down there); the abstracts for the session are here.

I love that valley. High, open, dry. Snow-capped peaks. And a little bit of tectonics, where North America has been pulled a little bit apart, west of the plains and east of the Colorado Plateau.


Sabine said...

Some of my field camp mapping work was in those mountains! It is by far one of the most beautiful places I've ever seen. Colorado is so magical.

Kim said...

They really are beautiful, aren't they? And a nice spot for field camp.