American River Confluence Earthcache EarthCache
American River Confluence Earthcache
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This is an earthcache; no container is required to be found. Simply visit the coordinates and read the following info and submit your answers to me. Enjoy the area!
Most of the rocks at the confluence were formed about 160 million years ago, during the Jurassic Period. At that time, the western coast of North American was located near the current California-Nevada border and the confluence area was part of the ocean bottom forming the continental slope. Over the millennia, fine-grained muds and silts were deposited over the basaltic ocean crust. California has been on the boundary of the North American and Pacific Plates for about the last 200 million years. The result has been that the state has been subjected to earthquakes, volcanoes and high heat flow for a long time, and the rocks have been squeezed, heated and faulted into the contorted metamorphic slates, serpentines and other formations. About 50 million years ago, the actual plate boundary ran close to the Auburn area and the Foothill Fault Zone was formed. Many of these faults can be seen in the area of the confluence and the site of the proposed Auburn Dam. The movement of the plates caused large cracks, or faults to open in the ocean crust, crushing the rocks along the edges of the faults. Although the fault system in the Auburn area is no longer active, it left zones of fractures and crushed rocks, which were more easily eroded than the surrounding rock.
When the Sierra Nevada Mountains began to rise about 5 million years ago the newly forming river systems followed the fault zones. The steep sides of this river canyon, with broken rocks in the bottom, and the abrupt right angle turns in the rivers are indicators of this tendency of rivers to follow the faults. The rivers in confluence area make a series of right angle turns. These abrupt changes in direction are often the result of water following old fault zones that are made of crushed rock and thus easier to erode.
INTERESTING NOTE: Many wonder how the Mountain Quarries RR Bridge received the nickname ?No Hands Bridge.? During the early years of the Tevis Cup Trail Ride from Squaw Valley to Auburn, people often commented that it must be dangerous to ride across the bridge without any guardrails. In jest of these fears, veteran rider Ina Robinson would drop the reins on the neck of her Arabian horse, hold out her arms, and say ?Look, no hands?. Gradually the expression became a common name for this bridge.
To log this cache, please answer the following questions:
1. GC number and name of cache on first line
2. Number in your group.
3. Note the two branches of the river as they meet at the confluence. Are they both similiar in color or different? If different, why do you suppose that might be?
4. How do you think the north and middle fork were formed?
5. Do you think this is an active earthquake fault area?
6. IMPORTANT: To confirm your visit, about 100 ft west of GZ, there is a brown sign with white letters that says "Fee Area". In the lower right part of the sign is a round sticker. What words are on the sticker? Without this info, your log will be deleted
7. OPTIONAL: Take a picture of yourself and/or the confluence behind you.
Thanks for visiting the confluence! I hope you enjoyed visiting the area.
Please send your answers to me by message or email.
REFERENCE: www.ohranger.com/american-river-north-middle-south-forks/poi/confluence-interpretive-trail
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