Welcome to the San Joaquin River! Find an access point to get a nice view of the stream, but do not go in. The currents CAN be dangerous!
Background:
The San Joaquin River is the largest river of Central California, spanning over 366 miles from the rocky Sierra Mountains through the Central Valley, out to the coast. The river is a vital water supply for California. Because of its permeable nature, it is underlain by one of the largest aquifers in the Western United States. The lower river is also a slow-moving, meandering type, making it one of the most heavily diverted and dammed streams in California. The route of the river was caused by the natural boundaries. When the compressional forces on the North American and Pacific Plates got to be too much, they uplifted, creating the Californian Coast Ranges we know today. This had another result. It formed and enclosed basin, what we call the Central Valley. The river snakes through here, unable to overcome the uplifted mountains in its path.
Geology:
The upper 98 miles of the San Joaquin River, which we are not focusing on in this lesson, can be classified as a steep gradient stream as it winds through the rocky Sierra mountains. It continuously erodes the hard igneous and metamorphic rock of the Sierras.
The lower river, which is where this Earthcache takes you, spans 268 miles, and is classified as a meandering stream. This makes the majority of the river a "meandering stream." Meandering streams come about when the area of flow is low gradient, or low slope, meaning the water is not rapidly moving at a strong downward angle. A low slope terrain means that the stream begins to wander, carving its own path through the ground. In this case, the stream is underlain by sediment up to 6 miles - 9.5 miles deep. Bedrock is not struck until below all of this permeable sediment, allowing easier erosion and meandering. The river wanders about making curves and turns as it goes. These sharp curves constantly erode the outside bank.
The fastest moving water along a curve is naturally toward the outside bank, and likewise, the inner bank of the curve is home to very low-velocity water flow. The faster water erodes the outside bank and deposits the sediment on the inside. This results in a steeper bank on the outside, and a gradual slope on the inside. The constant erosion and pressure of the fast moving water widens the banks of the river over time.
River meanders can get so curvy over time that they form oxbow lakes.
An oxbow lake is a lake formed by a river that had bent back and touches itself, creating a more direct route for the river, ultimately cutting off the curve. The curve is now the oxbow lake.
Logging this Earthcache:
Using your new knowledge of the San Joaquin River, send me a note with the following:
1) The name of this Earthcache.
2) The number of people in your group.
3) At this point in the stream, are you standing on the inside or outside of a curve?
4) What bank (near or far) is home to the most erosion?
5) Is this point close to creating an oxbow lake?
6) What you thought of the lesson and any pictures you would like to share! (optional)
Have fun, be safe, and enjoy!
Sources:
--http://www.onegeology.org/extra/kids/earthprocesses/meanderingRivers.html
--http://www.geocaching.com/geocache/GC1QN2P_yosemite-valley-river-meander
--http://en.m.wikipedia.org/wiki/San_Joaquin_River#Geology