UPDATE JANUARY 2025: The landowner has decided to remove the erratics from the property, apparently with the assistance of explosives. I've decided to keep the EarthCache going. Please message me the answers to the questions below and take a picture of yourself showing what the area looks like in its current state. At the very least, this spot now provides a good opportunity to reflect on the human impact on geology.
Here are what the erratics looked like when I visited in 2021:
Here are the remnants of the erratics in January 2025 (from 7oakley's log):
NOTE: If you can see the erratics without getting out of your vehicle, the attributes and terrain levels apply. However, if you are needing to exit your vehicle to see them due to length of vegetation etc., it is no longer wheelchair accessible or kid friendly. Please use caution if you can't complete this EarthCache from inside your vehicle and respect private property.
Farmers plowing their fields in the Willamette Valley periodically turn up peculiar rocks that don’t seem to fit with the local geology. Granite, for example, is out of place in the thick, fertile sediments around Albany: it’s a metamorphic rock, formed by eons of heat and pressure deep under the earth, more fitting for Montana than this part of Oregon.
Looking east from these coordinates, you will see, in the middle of a plowed field, several immense blocks of granite. The farmers who have owned these fields have steered their machinery around the boulders for generations, and as smaller rocks have turned up under the blade, they have been piled here as well, creating a monument of sorts to a peculiar episode in geologic history.
The fact is, these rocks probably are from Montana. They are evidence of one of the most cataclysmic series of floods ever to occur on the face of the earth. Between 15,000 and 13,000 years ago, massive glaciers impounded a vast lake in northern Montana called Lake Missoula. Decade by decade, the lake grew behind its frozen dam, until finally it reached a size great enough to break through, releasing a flow of water that has been estimated at ten times the volume of all of the rivers in the world today. The flood rushed down the Columbia River drainage, scouring rocks and soils across northern Idaho and eastern Washington. At Portland, the water was so deep that it backed up into the Willamette Valley as far south as Eugene.
After the flood subsided, the ice dam, and Lake Missoula behind it, reformed… and eventually broke again. The cycle repeated dozens of times over a 2,000 year period.
The rocks you see here were carried here by one of those floods. Geologists call them erratics, because they are anomalies in the local geology. Your mission, to complete the requirements of this Earth Cache, is to complete the following tasks:
- If possible, take a photograph of yourself or your caching party with these rocks in the background, and submit it with your log. Please do not trespass on private property; the rocks can be seen from the public road.
- Answer the following questions in an e-mail to the cache owner (do not post the answers in your log). This will require some research, but there are excellent resources available online:
- a. First, how did these rocks get here? (Hint: they’re too big to have been washed this far up the Willamette Valley by simply being tumbled along the ground in the flood. There’s another factor at work as well.)
- b. How deep were the floods at this point? (Hint: Don't confuse the depth of the lake with the elevation of the lake's surface. Evidence around the Willamette Valley places the lake's shoreline at about 400 feet elevation. Based on the elevation you measure at this earth cache location, how far below the surface of the lake would you have been?)
- c. Name at least one other Missoula Flood erratic visible in the Willamette Valley.
Thanks to K2D2 for geologic research and to djbach for field research in preparing this EarthCache.
