Basalt Grinding Rocks Earthcache EarthCache
Basalt Grinding Rocks Earthcache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
The rock that the GPS coordinates guide you to predates the settlement of the area by White men and women. It is from the native American era of North American History. It is located on the edge of a hikeable “Barlow Trail.”
Educational Info - Simple This roadside earthcache southeast of Metro Portland, Oregon attracted me as an earthcache when I was on a pilgrimage to the nearby Original Geocache plaque and GC92. I stopped to log a now-archived cache at this historic location and saw the unique geology nearby – thus this earthcache!
Geology:
The flood basalt provinces of which this is a part extends from the Klamath mountains and the high Cascade volcanoes to the south, the jagged northern exposure of the Sierra Nevadas further south, Mt. Hood and its range to the east, and the northern extent up into eastern Washington. The basalt is part of a series of “flood basalt” flows that unlike ordinary basalt flows (that cover small areas) these flows cover thousands of miles and millions of cubic tons of rock material. When the flood basalt flowed, it probably covered the thousands of square miles in only a few days, meaning the events that caused the flows would have been major catastrophes, altering the weather and biology of the entire region.
The basalt rocks that are visible at the surface are the combined result of three distinct time periods and three geologic sequences, labeled by some scientists as “before, during, and after” the eruptions that caused the flood basalts so visible in the region. Few rocks are visible on the surface to explain to geologists what the area looked like geologically before the volcanics of the Middle Miocene Era. What is evident is the quantity of basalt present over a vast area from the eruptions of this time period.
At the time of the eruptions, many believe that this area was ocean-front property to the Pacific Ocean, while large portions of what is now Portland were underwater as part of a shallow shelf.
Reasons for the Flood Basalt flow that formed this broad geologic area include the following scientific guesses:
1. The most popular is that a giant asteroid, several miles in diameter struck the earth in southeast Oregon, The resulting crater exposed the hot, melted rocks below the mantle, setting off the giant volcanics and resulting flow of super-heated basalt and rhyolite ash.
2. An alternative is that a large flooding event simultaneous with the series of volcanic explosions in the region released the large amount of flood basalt and rhyolite ash, working in a “chain reaction” as it were.
3.
In most regions, such as the Steens basalts of southern Oregon, the basalt flow covers a tremendous area with an aluminum-rich basalt.
After the flood basalt had been deposited this area likely looked very flat. However, since this was during a very active geological time period, other events, such as the continued action of Mt. Hood, fault action between the pacific and north American plates on the coast (San Andreas fault), the eastern Oregon ranges were formed to the east of the spot you are standing, pushing up layers of the basalt and ash, exposing them to weathering. Also during this complex period, younger volcanoes were formed and erupted, creating the upper layers of ash.
Basalt Rocks can thus be described as igneous rocks. Igneous rocks form from molten rocks, which are thick, fluid masses of very hot elements and compounds. There are many different types of igneous rocks. However, they were once melted and have since cooled down. The two major factors that influence the creation of igneous rocks are the original rock that was melted and the cooling history of the molten rocks.
The original rock could be any initial rock. Plate tectonic mechanisms move rocks throughout the crust, so even sedimentary and metamorphic rocks can become melted again in a subduction zone. The different types of rocks melt into different chemical magmas, which then is dependant on how it cools. In this case, this re-melting was likely caused by the subduction of the pacific plate under the north American plate.
Molten rock with different cooling histories and different chemical composition will form different igneous rocks. If magma cooled inside the crust of the Earth, the rocks will have larger minerals (and thus crystals) and referred to as plutonic or intrusive rocks. Molten rock that flows out onto the surface is called lava. These rocks are called volcanic or extrusive rocks.
History:
The Baker Cabin, located nearby is on the historic “Barlow Trail.” The trail was originally managed by the Barlow Party (from Independence Missouri) who didn’t wish to wait at the Dalles for weeks to raft their way down the river to the Williamete Valley. They saw what appeared to be a notch or crossing at Mt. Hood, so they took off over the mountains. It was tretcherous going, and the roadbuilding for the wagons was slow. They finally decided that there wasn’t time to build the road all the way to Oregon City before they got stuck in the winter snows. So, they build a cabin, stored their belongings and the wagons, and headed west over what is now Barlow Pass and arrived in Oregon City on foot, Christmas Day, 1845. The next spring, they went back for their supplies, brought them along the road they constructed, then Barlow decided to make the path into a toll road….The road was treacherous, at places with a 60% grade, but over the years improvements were made, and it was used as a toll road for almost 70 years until it was donated to the state of Oregon in 1919.
The historic Baker Cabin, available for tour nearby, is part of the Land claim made in 1846 by Horace and Jane Baker, part of the first party to use the Barlow road in the summer of 1846. Horace chose this location because he saw several large Basalt rocks nearby and knew that their hardness would come in handy for making grinding wheels. For years he mined the area for Basalt for use in making grinding wheels for mills up and down the rivers and valleys of the region.
Hard rocks, such as Marble, Limestone, and Basalt (volcanic igneous) have been used since before recorded history as places where native Americans gathered to grind acorns, corn, and other foods into flour. The rocks used as grinding stones are massive, often 20’ x 30’, creating “tables” from which multiple persons could work. The depressions in the rock were initially created by wind, water, or both (Metamorphic). This process is called erosion. These depressions formed places where the native Americans could place their items to be ground, then with the use of a pestle (hard cone-shaped hand-sized rock) could grind the items into meal. Over the centuries, the depressions would get deeper as the rock was worn away by the grinding action.
Today, grinding rocks are scattered over much of the west coast, with state parks and city historic parks showing off many of them for the public to see and appreciate. This one is not in a state historic park, but nonetheless you can appreciate it for its history and geologic significance to the inhabitants of the area. Without its presence, Native American life would have been drastically different.
Logging Requirements:
Send the answers to #1 - #3 to me through my geocaching profile.
1. List the name “GC1YH5V Basalt Grinding Rocks Earthcache” in the first line of your email. Also, list the number of people in your group.
2. Describe the texture and color of the rock that is used for grinding. Based on the description above, do you believe that these basalts are extrusive or intrusive?
3. Count the number of holes that were likely used for grinding.
4. (Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Post a picture with self and GPSr, the grinding rock should be visible in the frame. Be creative with this picture….its okay to pretend to be working!
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Resources:
Roadside Geology of Oregon
Wikipedia.org “Mt. Hood” and “Barlow Trail”
Igneous Rocks (visit link)
Barlow Trail and Baker Cabin Info: (visit link)
Grinding Rocks Info: (visit link)
Additional Hints
(No hints available.)