I didn't know what to expect from the Bitterroot Mountains of Montana. But from the moment I arrived in the Bitterroot Valley, I was nothing but amazed until I left three weeks later. Representing my time in Montana are three rolls of film from which I have chosen pictures to post on three web pages.
The reason I was sent to Montana was to be a field assistant to Donald Sidman, a PhD student at the University of Minnesota. His research area is the Bitterroot Shear Zone, which I will explain briefly. Millions of years ago, the rocks that now comprise the Bitterroot Mountains were many kilometers underground. On top of the Bitterroot Mountain rocks, which consist of crystallized magma (igneous rocks), were rocks formed from sediments deposited on the surface of the earth. These sedimentary rocks would eventually become the Sapphire Mountains. Very gradually, all these rocks were uplifted, as were many areas of the Rocky Mountains to form the high peaks we see today. As the rocks rose higher and higher, the sedimentary rocks began to slide east, off the top of the igneous Bitterroot Mountain rocks. It was in this process of sliding that the Bitterroot Shear Zone was formed. The shear zone is the area of mangled rocks near the sliding surface between the two rock bodies.
In terms of today's landscape, the Sapphire Mountains ended up across the Bitterroot Valley to the east. The shear zone is exposed in the eastern front of the Bitterroot Mountains, so shear zone rocks form the formidable wall of mountain forming the western border of the Bitterroot Valley near Hamilton, Montana. The shear zone itself is an area on the order of a kilometer or more thick (in terms of depth), that is angled such that it dips into the valley at the same angle that the mountain front dips. If this didn't make any sense, hopefully the photos will illustrate what I've been trying to say. Also, this has been a gross simplification of what actually happened and is not necessarily 100% correct, but it was the best way I could think of to simply explain the events. Write me if you have any further questions. brs8@dana.ucc.nau.edu
Let's start looking at these pictures and I'll explain a little more geology along the way.
Here are the two main characters. That's me, of course, on the left and that's Donald on the right. Both of the places featured in these two photos no longer exist the way they appear here. In what thay're calling the worst fire season since 1910, the majority of Donald's field area was consumed in the Blodgett fire. The sign I'm leaning against is the wilderness boundary sign on the Canyon Creek trail, the southern boundary of the fire. The ridge on which Donald's sitting is above and to the south of Mill Creek, right in the middle of the fire.
This photo is from near where the picture of Donald was taken, but looking east instead of west. From the ridge above Mill Creek you can see the Bitterroot Valley and the town of Hamilton, MT. In the foreground is the forested mountain front that dips into the valley mentioned above. Across the valley are the Sapphire Mountains.
The photo on the left shows a pinnacle on the canyon wall north of Mill Creek. All of the north canyon walls have rugged features such as these, while the south walls are generally forested and gently sloped. We have no idea why this is. We do know, though, that the feature shown in both above photos of peeling like a onion is an erosional feature called exfoliation. In these rocks it was probably caused by alpine glaciation over hundreds of thousands of years.
On several days we had thunderstorms. In this photo you can see the northeast corner of Canyon Lake and a section of the man-made dam that holds it in. The trail to this lake is very steep and rugged, but there's evidence of a narrow-scale rail car system near the dam so my guess is that pack animals had to haul those heavy iron parts up the hill.
This is another nice view of the rugged north wall of Mill Creek Canyon. A few days before I took this photo I was looking down from the upper canyon wall. The entire depth of the shear zone is exposed in this wall, but since we're not rock climbers it wasn't easy to sample it.
Again, this is looking up Mill Creek from a nice perch high on the canyon wall. This hike/scramble took so much longer than we thought it would that it was completely dark when we got back to the car. In over two miles distance, we climbed nearly 3000 vertical feet following the ridgetop of Mill Creek's north canyon wall to its highest point. While many mountain trails are this steep, we were not following a trail so it took us much longer. When we summited the ridge I took the photo being used as a header on the page. You can see Mill Creek Canyon on the left and Sheafman Creek Canyon on the right. The photo looks west toward Idaho.
