One of the largest watersheds in Southern California, the Santa Ana river ends its 96 mile journey here at the Pacific Ocean. The river cuts through rocks in the San Gabriel Mountains dating over a billion years old, caring sediments all the way here to Huntington Beach. The river today mostly consists of street runoff and snowmelt in the winter. On the southern side of this bridge, there is a sidewalk where you can answer all the needed questions to get credit for this earthcache.
The closer the water gets to the ocean, the slower it flows which allows finer particles such as silt and sand to be deposited near the mouth of rivers, like the Santa Ana. The Santa Ana River begins its 96 mile journey in the San Gabriel Mountains, near Big Bear Lake. Other smaller creeks and tributaries also flow into the Santa Ana River, making it much larger. These creeks include Lytle Creek and San Jacinto River which go deep into the San Gabriel and Santa Ana Mountains, respectively. These mountains have similar geology, both with strike-strip motion. The rivers in these mountains carry dissolved chemicals and sediments to which are carried all the way to the ocean at this point. At the snowcapped peaks of the San Gabriel Mountains, the metamorphic rocks are dated to be 1.7 billion years old, while near the base of the mountains the granite rocks are dated at 75 million years old.
There are a few things to note when talking about sediment deposition from rivers. One thing, is that it depends on a few factors. Speed of the river (which varies quite a lot), size of the particle, and the calmness of the ocean. Let's discuss the speed of the river. The fastest part of the river is located in the middle, just below the surface. A common misconception is that middle of the river at its surface is the fastest, but due to wind this slows it down. The edges and shorelines of the river are always the slowest.
Rivers can deposit different sediment. Sand, silt, and clay are the most common, but during large rain storms and floods, rivers can move large rocks and even boulders. Silt is the smallest particle that rivers can carry. See the chart below for the particle and their given sizes. A thing to keep in mind is that the smaller the particle is, the calmer the water needs in order for it to be deposited. It's one of the reasons why sand makes up beaches, and not silt or clay. Silt and clay are suspended in the ocean waves until they are carried enough out to see where the water is calmer, and are deposited on the ocean floor.
During storm seasons (November - March), the river can flow quite fast near the mouth, making deposition difficult and only occurring offshore. Because the mouth is located in a highly populated area, much of the river is made of concrete basins rather than a natural river valley like Newport Back Bay. A concrete basin allows water to flow more quickly, to reduce flooding upstream. It also allows easier control methods to reduce pollution as it is much easier to see where the point source is coming. However, during flooding, natural rivers push larger sediments, such as boulders, to the sides creating natural levees and protecting the river for years to come. Most of the time, the river doesn't flood and brush begins to grow on these levees, soaking up water during rainy seasons. Plants protect the rivers in addition to the natural levees. With the Santa Ana being a natural river, but altered with concrete basins, flooding will occur more frequently especially in low lying areas near its terminus.
Works Cited
https://geomaps.wr.usgs.gov/parks/rxmin/sediment.html
https://en.wikipedia.org/wiki/Santa_Ana_River
http://www.geography.learnontheinternet.co.uk/topics/river_deposition.html
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
1. "Santa Ana River Terminus" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching. However, this is not required.
2. As you walk to the above coordinates, look for any signs of levees along the banks of the river. If they exist, tell me: are they natural or man made? And how can you tell?
3. Look at the river towards the Pacific Ocean. Describe the conditions of the water. How fast is it moving? Is it choppy or calm? What direction is it moving? Etcetera.
4. Describe the water clarity and quality. Can you see any sediments? If so what are the sizes or shapes? Explain.
5. As you walk back to your car, look for signs where the city has prepared itself in case of a massive flood. Do you see anything that would help prevent a flood (or tsunami) in a major storm?