|STOP 1 - SANDY RIVER CUTBANK|
The first stop on our field trip was only a few miles from our meeting place at Lewis & Clark St. Park. We visited a cut bank along the Sandy River. On the west side of the river, opposite the cut bank, was a point bar containing coarser material at the
top (upstream), and the finer material of the point bar pointing downstream.
There was a house here at one time. Behind us back across the street, we were able to see a very distinct gully. Down this distinct gully of which there was water eroding it, there came a mudslide, and it took the house into the Sandy river. The mudslide was very liquid, very fast moving, and it undermined the house. Word has it that the old man living there was rescued atop his house as it floated down the Columbia River. His wife was never found.
Having a house on a cut bank is definitely a very dangerous desicion. If you have a house on a cutbank, you can be gauranteed that at sometime the land under your house will go away, even if its not neccesarily on a cutbank
|STOP 2 - TROUTDALE FORMATION|
The main rock type at this formation is conglomorate and sandstone. What this tells you about what has happened here is that this is a former cutbank of the Sandy river. The size of the particles tells you that these are channel deposits deposited by th
e river with varying velocities of flow. Of course the conglomerate would be a result of much higher flowrates as opposed to lower flowrates to deposit the sandstone. This area is known as the Troutdale formation. Rocks at this area tell you that this
used to be part of a river bed, a very big river bed, and it is not an incised meander. What we have here are river terraces.
Quartzite, basalt, and some grey andesitic type rocks which would have defintely come from Mt. Hood are present here. The rocks are very smooth and very rounded, and they have been abraded significantly, meaning that they have travelled over long distanc es because quartz, being an extremely hard substance, is not going to be rounded easily. The quartzite found in this area did not come from the immediate area. Quartzite is not a local rock, and most likely came from Canada or from Montana in great flood s.
A nice weathering rind has developed on the rock in the picture to the left, and so that is one of things you are going to have in any kind of water environment. Where you've got water, you're going to have chemical weathering. On this rock you can see both physical weathering of the rounding and the abrasion that a river has done, and you can see the chemical weathering of the material as well in the fact that there is a nice weather rind on this rock.
A few hundred feet south of this area is a concrete barrier erected by ODOT to help stop mass wasting from occuring on this cliff. Ugly as it is, this is an effective method of preventing mass wasteing. They are trying to stop the mass wasting by a vari ety of techniques including netting to keep the cobbles from falling down. In areas where you've got the conglomerate that's undercutting, a good idea is to build it up with reenforced concrete and to put pipes in the concrete to get rid of any water whic h may be in the soil behind the concrete barrier.
|STOP 3a - WOMEN'S FORUM|
Looking across the Columbia River from our 3rd stop at the Women's Forum, you can see a nice rounded hill slope off to the Northeast. This rounded hill is actually a sheild volcano, much like that which Larch Mountain is.
There is a huge amphitheater shape here, and it is an enormous scarp, meaning we are dealing with an event of mass wasting. Most of the material from this event slid downhill and was washed away by the river, leaving us a very nice looking amphitheater s hape. This place is still not stable and it still has a tendency to slide, slump, or move, and probably more than likely this was a slump event, but nonetheless you have a very nice scarp that the road follows, and it follows it out to Crown Point which is why you have viewpoints along these parts overlooking the gorge.
|STOP 3b - CROWN POINT|
What you can see from Crown Point if you look down the river towards the west is there is a point where the river starts to widen. During the end of the latest ice age when the floods came down the river carrying an enormous amount of flood water filled
with boulders and large sized peices of sediment and cobbles, it slowed down, spread out, and deposited these materials when it reached this flat area. Coarser materials are deposited on the east end of the wide area, with finer materials being deposited
further down stream to the west.
As the intense flood waters were passing through this widening depositing huge amounts of material, the flood waters down by St. Helens got blocked off and backed up into the Willamette valley, so the Willamette Valley is where you can find the finest sed iments. All of this and you still had enough water passing through that they scoured out past Rocky Butte. Rock Butte happens to be the result of the scouring by the Columbia River and eroding of that material away.
There is some evidence that during this time at the end of the most recent ice age, along with an intense amount of sediments and boulders being carried down the river there were many instances where there would be a boulder encased in ice, yet only makin g up 20% of the entire mass of the object, meaning that 80% of the mass of the object was ice. This kind of object is very bouyant, and as it happens it is far more bouyant that just a boulder itself flowing down the river.
|STOP 4 - LATOURELL FALLS|
There are 3 different types of Columbia River basalts exposed here at Latourell Falls, those being the Grand Ronde basalts, the Frenchman Springs flow, and the Priest Rapids flow.
In this area at Latourell Falls you can very easily see an abundant amount of columnar jointing, which was formed because of the lava flows that have extensively covered this whole area. The flow ended up cooling, shinking, and then contracting, which it can do so vertically very easily. When the flow is cooling it has a tendency to contract inwards, but in such a large expanse as from Idaho all the way to Latourell Falls it can not contract as a whole and so it ends up contracting inwardly in these nic e hexagonal columns.
Another noticable feature in this area is there is a slight dip in the flow, going down on one side of the waterfall and then up the other side, resembling a valley. One of the theories for the formation of this area is that this is also an intercanyon fl ow. Because of the nice valley shape that this area has, flows most likely filled this up, and you have columnar jointing in this area not at a vertically straight formation, but more at an angle where it has flowed in the erosion-forming v-shape carved by the river.
What you can also see here is how a waterfall is being created. Where the waterfall is cutting back, in the cracks of the columnar jointing, water will collect, freeze, and expand resulting in the lower section craking and breaking off. This is refered to as frost wedging.
At the top of the flow it is not columnar jointed, rather it is brick-brack jointed. The part of the flow that is brick-brack jointed doesn't have the nice, long cracks that the columnar jointed section does, meaning that there is significantly less fros t wedging taking place and as a result the brick-brack jointed portion sustains much less erosion.
Another thing to point out is that it is always easier to erode between flows than in the middle of a flow. When a stream and a waterfall are in the area, it will erode inbetween flows causing them to "step-out." Most of the streams in this area such as Multnomah Falls have steps to them which are present because the fall will erode the top of one flow unit and the bottom of another flow unit at a faster rate than the middle of the flow units, leaving sometimes numerous steps that the waterfall then des ends down upon.
On the way back to the parking lot we stopped along the side of the trail to examine an exposed part of the flows. The first unit we looked at was a 25 million year-old formation, which tends to be more andisitic than basaltic, and is part of the origina l building of the Western Cascades. You are able to see the difference in age between this flow and the Columbia River basalts. The Columbia River basalts were erupted 15 to 16 million years ago. There are 3 different types of Columbia River basalts ex posed here at Latourell Falls, those being the Grand Ronde basalts, the Frenchman Springs flow, and the Priest Rapids flow. The Frenchman Springs flow and the Priest Rapids flow of the Wanapum Basalts are where the upper falls are, meaning that they are significantly younger (about 14 million years old) as opposed to 15 or 16 million years old which the base of Latourell Falls is made up of.
|STOP 5a - MULTNOMAH FALLS|
From our vantage point at Multnomah Falls you could see a large display of pillow basalts. The land here is made up of pillow basalts, meaning the basalt was erupted into water.
One of the things we could see was that off to our left there was some mass wasting that has closed off part of the hiking trail that goes further up the landscape, and as it happens this turns out to be a permanent closure meaning that we will never (leg ally) be able to hike up to that level.
Daina ended up telling a story of a wedding within the Multnomah Indian tribe where a great sickness came over the Multnomah's and the other tribe of the groom, and after much consideration the elders decided to offer up a sacrifice in order to stop the s ickness from taking more lives. The bride, one of the daughters of the Multnomahs was to be sacrificed, but after more consideration it was decided that they would not sacrifice her. As it happened, the night before the wedding she visited her fiance an d saw the sickness upon his face. After that she wandered away from the camp late that night and when she was nowhere to be found the next morning many of the tribesmen ran out to the falls just in time to see her throw herself off. The legend tells that at certain times you can see her face in the falls because of the way the rocks are shaped. Thanks for the folklore lesson Daina!
|STOP 5b - ONEONTA GORGE|
The Oneonta Gorge is a very unique habitat. Ecologically it is a very specialized area and contains some plants growing in it that grow nowhere else in the Columbia Gorge. In reference to the Davidian Cycle, the Oneonta Gorge would be in its youthful st
age while the Columbia Gorge would be in its mature or old age stage.
This gorge differs dramaticaly from the Columbia Gorge in the fact that is much narrower. The cause of a development of this sort lies in the fact that there is a vertical fault in the area. Faults are areas of weakness and where you have an area of wea kness you will have an easier time eroding in that area. Because erosion occurs at a faster rate inbetween two rock units rather than in the middle of any one rock unit, what formed the narrow gorge here was preferential erosion along the vertical fault.
As we walk down a path into the Oneonta Gorge itself we see many holes in the side of the gorge walls. In this area there are aquifers not exactly IN the basalt flows, but rather INBETWEEN the flows. At the point where basalt flows meet often times the soil will be red, which is caused by contact metamorphism, as baked clay turns into brick. Inbetween lava flows these are the basalt aquifers, though not in the basalt itself, most of them are inbetween the basalt flows.
|STOP 8 - CASCADE LOCKS|
Prior to Boneville Dam being constructed, Cascade Locks had funtioning locks on the south side of the Columbia River due to the river being impassable at this point. Various object and obstructions in the river would create huge cascading waterfalls at t
his point along the river, keep in mind the falls were not large and steep but rather consisting of a gentle gradient where there was a consentration of debris which would block passage up the river for boats and barges. Locks were installed so that the
level of the river could be raised and lowered in order to let ships pass.
Looking across the river and a bit to the west from Cascade Locks, we saw a mound of material that was deposited by an enormous landslide, that being the Bonneville Landslide. The source of the Bonneville Landslide was Red Bluff, which is located just sou th of Greenleaf Peak north of the Columbia River in Washington state.
The area of the Bonneville Landslide is slightly tilting south towards the river. In this area you mostly have basalt which is to a certain extent jointed and fractured. This basalt overrides what is called the Ohanapecosh Formation. The Ohanapechosh Fo rmation happens to be a formation that has been weathered and altered now into slipery red clays. When you weather and alter into slippery red clays you have basalts that have fractured on top of the clays that are tilted south towards the river. When wa ter gets involved with this area of basalts on top of the clays it becomes the perfect place for a mass wasting event because of the slick and slippery clays coupled with the fact that they are tilting downward towards the Columbia River.
At this point Daina again went into a Native American story this time dealing with the Kilikat tribe and the Multnomahs. As the story goes, there was a "bridge" that was created over the Columbia River that connected what is now Washington to what is now Oregon, with the Multnomahs on the south side of the river and the Kilikitats on the north side. As history shows, this "bridge" was actually a blockage of the Culombia River caused by an enormous mass wasting event that completely blocked up the river allowing people to literally walk across the river on a natural "bridge". When European-American settlers heard this story, they interpreted the "bridge" as being similar to thier man-made wood and stone bridges that Europeans and European-Americans had been able to build for many centuries now, and the story of a bridge over the Columbia River confused many white settlers to the area. These settlers ended up trying to discount any notion that "these savage types would be able to harmess the will or int elligence to build something so out of place in thier culture." Little did they know that the Native tribes of Oregon had no need to control nature and build a bridge, they were content with adapting to the land instead of manipulating it.
|STOP 9 - STARVATION CREEK|
The rest area at Starvation Creek had been closed, so as we arrived we parked right alongside I-84. Shellrock Mt., located south of the Columbia River in Oregon, and Wind Mt., north of us in Washington, are both creeping towards the river ever-so-slightl
y, causing the river to narrow a bit in this area.
Across the Columbia River to the north from Starvation Creek you are able to see a nice example of a dipping block right into the river. The picture to the left illustrates how this anticline is dipping into the Columbia River. The dip on this section is about 35 to 40 degrees with the strike being perpendicular to that. This is not a true dip though, because it is not on end to the angle. This would be considered and apparant dip (meaning you would say this has an apparant dip of about 35 degrees to t he southeast).
|STOP 10 - MITCHELL POINT|
Across the Columbia River from us (in the background of the above image) you can see a nice flat top section that is part of an intercanyon lava flow that came down the Salmon River and which essentialy filled up the channel of the river. The Salmon Rive r then had to cut a channel along one side of it, that being the west side of the flow where the river now comes out into Drano Lake. The edge of the intercanyon lava flow that blocked up the Salmon River is the easiest place for the river to cut through, and that it where the river cut through and now comes out, whereas it used to come and meet the Columbia in the entire valley there that is now filled with the flow.
Wind Mt. creep, also Wind Mt and Shellrock Mt being diorite stocks. Shellrock Mt. and Wind Mt. creeping present problems from road building on the Washington side of the Columbia River because they are weathering and crumbling and falling, and in some rec ent cases there have been a few major rockslide that have fallen onto the highway along the Washington side of the river. The material in the Washington side of the river is distinctly different from the Columbia River basalts that you see everywhere els e around this area (being that it is coarse grained and almost granite in texture, and also having an intermediate composition).
Looking to the southeast from our position in the parking lot at Mitchell Point, we can see a multitude of rock formations with a dip to the southeast as well. Numerous lava flows exist in this area, those being the Frenchman Springs Memeber (that being the oldest flow), and the Pomona Member, being the younger as it lies on top of the Frenchman Springs Member and also on top of a conglomerate layer which is present in some place inbetween the Pomona member and the Frenchman Springs member.
|STOP 11 - HOOD RIVER|
As you come out of the Cascades and the Columbia Gorge there is a significant change in vegetation. This situation is prompted by the Cascades themselves. The rainshadow effect that you get because of the Cascades will dump most of the rain on the west
side of the mountain range and less rain on the eastern side where Hood River is located. The weather at Hood River in relatively mellow compared to the rain, cold, and wind that are frequent on the western side of the Cascades. This is turn means that
the vegetation out near Hood River will be such that it will be able to thrive in a much drier climate.
The other thing to note is that in this area of Hood River there is a place where the change in elevation is dramatically reduced, represented on a topographic map as an area with many close contour lines giving way to an area with contour lines that are few and far inbetween. The reason for this change is the fact that there is a fault present where the Hood River valley is - where the east side of the valley is higher than the west side. This fault is named the Hood River Fault. The east side of the fault is being lifted above the west side, meaning that this is a normal fault with an element of both compressional stress creating the anticlines and synclines, and tensional-rotational stress creating a small amount of extension.
The material that the Hood River cuts through is glacial till, meaning that this is an area where a glacier was present and there was a significant amount of deposits of glacial till most likely at the end of a glacier or it was deposited during the reces sion of that said glacier.
|STOP 12 - ROWENA CREST OVERLOOK|
Our last stop on the trip was at the Rowena Crest Overlook up above and across the river from the town of Lyle, Washington. From our vantage point on the overlook, you can see a mass of material that has jetted out into the Columbia River, and this is ye
t another mass wasting event. In this case it happens to be a slump. Because it is a slump it has a concave section with blocks that are very visible and tilted up because they have slid down the slump and stopped along the way. This concave surface m
eans that there are rocks in this area that are still sitting here with the same surface that they once had when this area was flat. The cause of this mass wasting is landslides predominatly, but floods have also played a part in the events.
If you look across the river to the town of Lyle, Washington, you can see that Lyle is actually on a gravel bar. If you look up and to the west of Lyle to the other side of the stream that comes into the Columbia River there is a rounded, hillish-like ar ea, and even further to the west there is another mound-like area, and these are all gravel bars. The unusual size of the gravel bars will tell you that these are not normal bars that happen within normal events. In fact, these gravel bars are from the Pliesticine Floods. The floods tore through the area and scoured off the basalt and anything else that was here and left gravel bars several hundred feet above the river level. The Pliesticine Flood ran through this area at speeds up to 65 mph and took only a couple days to empty the big glacial lake behind which it was damned by ice, emptying all of that through the gorge and scouring it out, that is the reason why much of the area here is very smooth, because of the scouring.
To the Northeast of the overlook there is a section on the north side of the river where horizontal layers of rock can be easily seen, and there is a section in the middle of these straight layers where it drops down. This is a drag fault that has dragge d that set of straight lava flows downward towards the river. This feature is the Ortley Anticline and the Ortley Fault.