American Rivercut Earthcache EarthCache
American Rivercut Earthcache
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As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
Getting there: This earthcache is in Fair Oaks near Bridge Street. On maps, this road seems to cross the river, however it is a pedestrian bridge ONLY over the bridge, thus you must decide whether to park at the businesses on the north side of the bridge OR (preferred) drive around to the south side of the river, park in the park, then walk across the bridge. Either way, there is about a 2/10 to 3/10 mile walk from available parking to the start of the uphill climb.
This earthcache has some dizzying heights without railing or protection, so watch your step!
THE CORDS ARE FOR THE ENTRANCE TO THE TRAIL. YOU WILL NEED TO GO UP THE TRAIL TO THE TOP OF THE HILL THAT OVERLOOKS THE RIVER TO COMPLETE THE CACHE.
Geologically:
The Central Valley, that the Sacramento area is a part of, is a sedimented valley formed by years of sedimentation from the inland lake that formed in the area after the coastal ranges cut off access to the sea in the ancient past. The rivers flowing down from the rising Sierra Nevadas to the east filled the valley (lake) with meters of silted sediment that has turned into several types of siltstone/ sandstone. Within the layers you can find grains of granite, sand, soil(silt), and traces of gold. However, most of these traces actually come from the time when hydrolic mining in the hills blasted millions of metric tons of sediment into the riverways of California (see other earthcaches for details concerning this event). As the San Francisco Bay developed and the lake drained, rivers like the American River cut into the soft layers of sediment and metamorphizing rock (silt dirt turning into stone under pressure). What you see before you is the cutting of the river through these layers of metamorphized sediment.
Erosion:
On the Sacaramento and American Rivers, the average rate of erosion from 1993-2001 (an extensive study is available online), is 2.5 meters / year. This calculation is based on aerial photographs taken since 1934, which show the river at significantly less eroded levels. The erosion rates vary dramatically. The largest factor the affects the erosion rate is the amount of sand in the soil. The higher the sand amount, the higher rate of erosion.
Obviously, erosion has both positive and negative effects.
Positive: erosion helps create new areas for vegetation growth and thus new places for animals to live. The new soil left in river curves and on aluvial plains also provide fertile soil (think farming).
Negative: Once bridges, roads, and buildings have been built in an area, it is hard to adapt to erosion, Especially if it eats away at river banks that have these fixtures “attached” close to the edge. A perfect example of this erosive effect are the trees near the cords that are more than 60% “hanging” out into the air....no longer firmly attached to the bank!
It is probably comforting to note that erosion has been largely halted in the 20th and 21st centuries by the pletoria of dams on this river....It is unlikely that the river channel will change much in coming years!
Logging Requirements:
Send the answers to #1-#3 to me through my geocaching profile.
1.List the name “GC24F9R American Rivercut Earthcache” in the first line of your email. Also, list the number of people in your group.
2.At N38 38.236 W121 15.883 ---
Based on the Palm Tree visible BELOW, estimate the HEIGHT you are above the river below.
3.Based on an erosion rate of 2.5 meters per year, how many years did it take to cut this river? Does the soil at your feet seem to contain a high % sand or very little sand? Based on this info and the description, is the erosion rate HERE likely greater or less than the average?
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 of yourself and/or your GPS with your log that shows the bridge in the background.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Congrads to Twiddleflip and Team Pluto for a Co-FTF on 3/6/10.
Resources:
Alt & Hyndman, Roadside Geology of Northern andCentral California. Mountain Press Publishing. Missoula: Montana. 2000.
Journal of the American Water Resources Association: www.americanriverwatershed.net/Files/2994.pdf
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Treasures
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