Friday, March 02, 2007
Friday Geology Pic: Lewis, Clark, and Imbricate thrusting
I've been re-reading Undaunted Courage by Stephan Ambrose, a historical summary of the Lewis and Clark expedition. I forgot a lot of the crazy things they did: For example, Lewis was shot in the ass right at the end of the trip.
One interesting point that Ambrose makes (aside from prefacing every fucking thing with "they were the first white men to....") is that Lewis, while being an excellent naturalist, wasn't a very good geologist. Apparently, he did have a copy of Lyell's seminal text with him, but he rarely (almost never) commented on geology.
I thought this unfortunate, because of the route they took. It happens to coincide with where I went to field camp.
Field camp, or the class that teaches you the basics of field geology - the collection of geologic data, is one of the highlights of any geologists training: Love field camp, and you will be a geologist forever, no matter what...Hate it, and you may never be a good geologist.
I personally Loved field camp, and since my own field camp experience, I've been teaching assistant on 3 years of field camp at UNLV, and another 3 years of Leading my own field classes.
Blah blah blah, who gives a shit?
...Back to lewis and clark...During the expedition, Lewis and Clark needed to meet up with the Shoshone Indians near the 3 forks area of montana in order to get a guide and information about crossing the mountains out to Idaho and Oregon from the plains of Montana. Coincidentally, The three forks area in montana is where Sacagawea was from.
its also a place where some of the best exposures of Cretaceous and Tertiary-aged faulting and folding are exposed. my field camp instructors took us up and down the jefferson river valley mapping all sorts and scales of hangingwall and footwall thrust faults, folds, regional scale folding and faulting..its truely the place where I really learned about and loved structural geology. Within the side of entire mountain flanks are exposed massive anticlines and synclines, faults, joints and other stuctures.
There's a complex geologic history in the region, that is brilliantly exposed in the mountains as you travel through the area.
I took a lot of pictures at field camp, but above is one of my favorites. It was taken in the Jefferson river valley, not more than 10 miles from the 3 forks junction. In addition to showing me much younger, skinnier, and healthier, the mountain behind me is a great example of Imbricate Thrust Faults.
if you look just to the left of my head, you see a thick whitish bed of limestone that is dipping to the right side of the picture. On the left side of my head is another thick whitish bed of limestone. Then again more to the right, but less well exposed is another whitish bed of limestone. These are THE SAME rock unit that have been pushed up and faulted next to each other. Its like if you took a piece of floor tile, cut it into pieces, stacked the pieces on top of each other, and then tilted them so that when you looked at the stack edge-on they would be all leaning against each other.
Lewis recognized how great the foothills and mountains in this area, and described them on several occasions, both on the trip to the pacific, and on the trip back. Unfortunately, he didn't know the geology, Its too bad he didn't understand what he was looking at, or his passages would probably have been twice as exciting.