First – the caching type stuff. Parking is nearby. One of the conditions for the Earth Cache is that it not degrade this park, so please pack out your own litter, and even better, practice some ECITO (Earth Cache In, Trash Out) and help promote our hobby. You may want to park closer to the proof of presence waypoint at some times of year. If the Willamette water level is high, this site may be flooded and the cache unavailable. It may be muddy at other times - be prepared. Also, the park is only open sunrise to sunset, so do not attempt at night. Email me your answers, do not post them. I reserve the right to delete logs or images that provide spolier information, please do not post such.
The soils of the Willamette are based on Volcanic and sedimentary rock, with some formations of shales, mudstones and turbidites (marine slump deposits) generally from the Eocene. On top of this lie the Columbia River Basalts, deposited during the Miocene. In that late Pleistocene/early Holocene when the Cordilleran ice sheet blocked the flow of the Columbia and the Glacial Lake Missoula drained, with a force ten times greater than any river flowing on earth today, the Willamette Valley became a pond, which resulted in the Willamette Silts, layers of horizontally bedded clay silt and sand up to 100’ deep.
The Willamette has been working on eroding since the late Pleistocene, however, much of the river downstream is static, due to the basaltic bedrock. The Willamette is the 19th largest river in terms of annual discharge today and while its total is less than the Columbia, when adjusted for drainage area, the Willamette has the highest discharge rate per drainage area of the twenty major rivers in the USA. The area around Irish Bend shows the effects of some of this force, and how nature and man have responded.
At N 44 291.787 W 123 13.201 you will find a textbook example of the river’s work exposing both the Willamette Silt and the Linn Gravels layers across the river.
While man made improvements have greatly cut down on the force of the Willamette River, Master’s research by Joshua Wyrick (see the link above, much of this information was taken from his research) suggest the presence of the Linn Gravel layer here has helped put a natural meander limit on the course of the river. Aerial Photographs and survey maps show the river altering course and roads being abandoned until around 1956, at which time the course of the river begins to stabilize, these are available in the second part of his paper and are interesting to observe the recorded change and stabilization over the last century plus.
Questions –
- How many layers do you see across the river in both the Willamette and Linn deposits? What are the differences between the layers?
- What is the total height of the exposed bank in feet, your best estimate?
- To the right of the bank, as you look from the listed site, you will see a man-made revetment, part of man’s attempt to stabilize the river. What do think this revetment is made of?
- Why do you think the revetment doesn’t continue? You may want to consider the presence of igneous rocks (those with vescular holes in them) at the site.
- (Proof of Presence) At N 44 21.777 W 123 13.299 is a sign with nine lines of text – what does line six say?