Palouse Falls

The first year we lived here in Oregon, just after one of my geology classes had covered the Columbia River Basalts, a couple of my students took a weekend trip to Palouse Falls. They came back from their trip excited because they had been able to take what we had talked about in class and apply it to what they saw at the falls.

Because the Falls are nominally on the way to Spokane, WA or Moscow, ID, I would try and make a side trip to the falls on one of our trips for one of Sam's athletic competitions. Every time we would make the trip, I would plan on stopping on the way home, but something always came up (a snowstorm, a sick traveling companion, cold weather, a wrong turn, a snowstorm, lack of daylight due to a championship softball game, another snow storm) and I hadn't yet made it to the falls. I was finally able to make it this years when I had a couple of extra hours on a trip to Spokane.

The Palouse River cuts a narrow canyon through several prominent layers of Columbia River Basalts, and at the lower falls, there is an alcove where the river drops 56.6m (186ft) into a large plunge pool. From the falls, the river continues about 6 miles to where it empties into the Snake River above Lower Monumental Dam.

Lower Palouse Falls

It was a nice spring day, so marmots were out sunning themselves on the cliff side. It was a great lesson in camouflage that when we got about 5 meters away it took a while to pick the two marmots out from the dark basalt rocks along the edge.

Two marmots enjoy the spring sun.

From the main parking area, a short trail heads north to an overlook of the Upper Falls. From the overlook, a trail leads down into a wide side canyon and to the upper falls. Because we were limited on time, we only hiked down to the level of the UP Railroad grade for a view down the canyon.



View of Upper Palouse Falls from the Railroad grade.

At the base of the cascades of the North Falls, the river makes an almost 90 degree bend. This bend is because during the Ice Age Floods, the path of the Palouse River was diverted into a series of NW-SE trending faults.

The ancestral Palouse River used to follow the Washtucna Coulee to Kahlotus and Connell some 50 miles before ultimately discharging into the Columbia River near Hanford). But the volume of water resulting from the Ice Age Flood pushed the river out of its ancestral channel. The steeper gradient of the fault dominated channel allowed river to carve a deep enough canyon to capture the flow path after the floods receded. The abrupt transition from the ancestral channel into the nearly straight fault driven system can be seen in this Google Earth screen shot.

Google Earth image showing the fault channel of the modern Palouse River

Fall Field Trip Part I - Pendleton to Ukiah

Last week I took two students on a drive to look at some of the rock outcrops in the area. I often complain that all you ever see around the area are Columbia River Basalts, but we did find some other outcrops too. Our first stop was a whole 1/4 mile from the college parking lot, at the bottom of the hill. From there we got a close up look at the ubiquitous CRBs in the area. The three layers seen in this photo are accross the river valley from the same (but better) formation I posted about in September.

The top layer, characterized by the grayer more blocky rock is the Frenchman Springs member of the  Wanapum flow. The broad reddish band in the middle is the Vantage soil horizon, on the edges of the horizon there are some baked contacts where the clayey soils have been baked into a marble. At the bottom, looking more like a talus field in this image is the Sentinel Bluffs Member of the Grande Ronde Flow.

In class we have been talking about weathering and sediment transport in class so our next stop was at some Late Miocene deposits in the McKay formation. The alluvial beds are mostly sand, gravel, and cobble, but on some of the north facing slopes there is also Pleistocene Loess.

While poking around, one of the students noticed some mechanical weathering on one of the cobbles, so we could nicely compare the differences between material that had freshly weathered and materiails that had been rounded through transportation. 

The next stop on our field trip was a road cut through Cretaceous aged intrusive outcrop of granodiorite just north of Battle Mt. State Park. The outcrop is heavily weathered with a 5m pile of scree at the bottom, and a nonconformity with the Miocene Grand Ronde Basalts above it.

From the road, the cliff looks real nice, but when you get up close to the rock you notice it is full of quartz veins and really crumbly. We investigated whether it was just excessive surface weathering by digging in 10-15cm with the rock hammer, but it still came out crumbling in our hands. Because the formation is near some thermal springs, we posited that much of the rotten nature of the rock was due to historical contact with some of these thermal features.

Eddie Looking at the quartz veins, note a small bird hole just above his hand

Most of the quartz veins were fairly competent, but there were some that had almost pure quartz powder. This vein was fillled with quartz grains that had the size and texture of white flour.

After Battle Mountain we continued on 395 to  Ukiah and the second part of the Field Trip was over the Blue Mountain Scenic Highway from Ukiah to Heppner.

What I see on the way home from work

So every day coming home from work, I see this outcropping on the side of the interstate.

In the big picture it is a fairly typical outcrop of Columbia River Basalts that are ubiqitous in our area, but there is more to the story. There are really two layers of Basalts here separated by a layer of baked paleosoils.

What is interesting about this picture is it represents the horizon between two separate flows. The upper layer represents the Frenchman Springs Basalt, the lower member of the Wanapum Flow. The Wanapum flow originated from dikes between Pendleton and Kennewick, WA about 15.3Ma and covered.

In between the two basalt flows, there is a baked layer of paleosoils 0.5-1.0 m thick. This red layer is the Vantage Soil Horizon and represents soils weathered in 200,000 years between flood basalts.

The older  (lower) Grande Ronde Flow originated NE Oregon ending about 15.5 Ma.  The Grande Ronde flow was the most extensive of the CRBs with as many as 18 individual flows covering up to 160,000 km2 with at basalts. Sentinel Bluffs layers are generally only 10-30m thick, but some of the lower Grande Ronde flows were over 80m thick.



Figure Taken From http://geology.isu.edu/Digital_Geology_Idaho/Module10/mod10.htm



This particular member of the Grande Ronde Flow originated from the Chief Joseph Dike Swarm, a series of dikes about 100 miles NE of this outcrop. This is interesting in the fact that today, these dikes are separated from this outcrop by the broad anticline which makes the core of the Blue Mountains

.