The Molalla River, Oregon

The Molalla River at dusk

This week my partner and I had the chance to visit the Molalla river with Holly, a close friend of ours. She grew up close to the river and told us stories of her time here as a kid. The one I found most fascinating was about the major flooding in 1996 that pretty much changed the dynamics of the Molalla. As a tributary of the Willamette River, the Molalla was adversely affected by the flood of 1996. This was that once a century flood that nearly inundated downtown Portland, Corvallis, Salem, Eugene and smaller towns along the Willamette.

The Molalla River from the opposite direction. Notice the large cobbles the further up the beach from the river?

Prior to the flood there used to some small rapids in the direction of the grassy area on the water. I’m not a hydrologist, so I can’t really elucidate as to how the rapids were affected by the flood waters. I can speculate that some large rocks, portions of the river bank and some trees were probably displaced from along the river bed and that somehow changed the dynamics of the river. What I found really interesting was the juxtaposition of the cobble sized sediments against the sand particles closer to the water. I imagine those cobbles were deposited by the flood when the water had the energy necessary to move sediment of that size. The sand was deposited at times when the Molalla didn’t have enough energy to keep the particles suspended and carry it further down river. Like I said, I’m not a hydrologist so my interpretation is probably flawed. Suggestions anyone? (I’m looking at you Lockwood and Anne 😉 )

For the love of Southern Oregon

Glide 1
Last week I had the opportunity to travel to Glide, OR. and see my partner’s family. Glide is located in the Umpqua Valley of Southern Oregon and, in my opinion, has some of the best geology the state has to offer. I realize I’m making a tall statement when the Columbia River Gorge, Mt. Hood, and the John Day Fossil Beds (just to name a few) reside within the state boundaries. However, I love this part of the state because a lot of it resides on what used to be the ocean floor. Thanks to uplift and erosion (either man made or river cut), that ocean floor can be seen at the surface. And with some help from fellow geo tweep, Ron Schott, I was able to learn more about the geology of the area.

Glide basically lies at the foot of the Western Cascades on what was probably Oregon’s old coast line. Most of the rocks are from the Eocene era (~30-50 mya) and are composed primarily of basalt and sedimentary rocks.
Glide 2
Interestingly enough these same basalt flows are roughly the same age as the Clarno Formation of central Oregon.

Both of these images are of the same out crop exposed at the road cut in Glide. I can’t get into the details of the geology too much because, quite frankly, I don’t understand it well enough to offer up a sound explanation, but I’m working on it.