Before Lake Mission Viejo was a lake, it was farmland. It was the only useful thing that this area could be. After all, it was very hilly. Not good land to make a wagon road through or houses, let alone a city. Up until the 1950's that is what everyone thought about the area around Lake Mission Viejo. In the 1970's the idea for a lake in Mission Viejo came about. Construction began soon after, but to everyone's surprise, fossils millions of years old were discovered at the bottom of the hole which would be Lake Mission Viejo. Whale fossils, similar to the one on public display off of La Paz Rd (This is also another eartcache, BONUS!) near Interstate 5 were found among the dirt. How did a whale fossil get 700 feet above sea level? The answer can be found in geology.
GEOLOGY
Before we can discuss how a whale got here, you must understand what a fossil is and how they are formed. In this case, we'll use whales as the example. To make things simpler, we'll talk about fossils in general. When sea life dies, they fall to the bottom of the ocean. Over millions upon millions of years, sediment that has been carried by the ocean pile up on the dead organic matter and begins to crystalize and form hard rock. The rock is denser than the soft sand below so it sinks and when it does, the temperature rises. When it gets above a certain point, the rock melts and takes the shape of the dead animal. Due to geologic forces, the the newly made fossil is brought up to the surface under miles of rock. As the terrain rises, so does the location of the fossil as it gets closer to the surface. When the fossil got here, it was only about 70 feet below the surface. Here, you are 700 feet above sea level. This is because the organism that made the fossil's imprint has impurities such as organic matter that is burned off and become less dense and rises again. This is how it got there, but not why it got there.
This can be answered by knowing that tectonic movements cause land to move. Land moves because of convection currents in the earth. Similar to when you cook pasta on the stove and you see pasta sink and rise in the pot. This is a natural process of high or hot temperatures want to go to low or cold temperatures. This is one of the laws of nature, that everything tries to balance out. High pressure goes to low pressure to find a balance. When this happens in the earth, we get cracks called faults. We all know about the San Andreas Fault, which is only about 60 miles from this location. This fault was not always here.
40 Million years ago (mya), there was a plate that doesn't exist today called the Farallon Plate. It collided with the North American Plate heading north east at about a rate of 2 inches per year. This plate had fossilized marine life and it was carrying it right to California. About 20-25 mya, we had the creation of the true San Andreas Fault. Because the Farrallon Plate was a convergent plate (meaning a subduction zone at the intersection of the North American plate) heading north east, it made the San Andreas a transverse (or slip-fault). This may not make a whole lot of sense, but think about it as if the Farrallon plate went all under the covers at bed time, but never woke up. The covers being the North American Plate. The entire Farrallon plate disappeared under the North American Plate where is kept going deeper and deeper into the earth's core where it was melted and fused with the current North American Plate. Most of the fossils were lost, but some, likely less than .01 percent were part of the new fault and a new plate. The new fault being the San Andreas and the new plate being the Pacific. Look at the diagrams below to get a mental picture.
Some ancient shells have also been found in the pit when the lake was being constructed. The same geologic forces that bring fossils to the costal ranges of southern Orange County, can also bring ancient sea shells. Based on where the organism lives in the ocean, gives it a unique shape. For instance, if it lives near the surface, it will have a more flat shell because of the hard hitting waves. If the animal live near the abyssal zone, it will have a more circular, more spherical shape to help combat the intense pressure. Here's a chart that will tell you where the different shells are found and their depths. You will need to keep this chart in mind at GZ.
Now that you are familiar with the geology of the lake's location and the fossils that are found here, we can then talk about the hydrology of the lake and how that effect the local wildlife.
HYDROLOGY
Now that you are familiar with the geology of this lake's location, we can discus the hydrology. Lake Mission Viejo is part of an important watershed that feeds into the Pacific Ocean at Doheny State Beach in Dana Point. This part of the water cycle happens in a watershed. A watershed is an area or a ridge of land that separates waters flowing to different rivers, basins, or seas. Basically, its everything but a river. Watersheds are normally seen during rainy seasons of the year and for Southern California that's December to February. Below is a map of the major Southern Califonira watersheds that we have.
When it rains, water flows from the sides of the costal mountains into the rivers which then feed into the ocean. The Oso Creek flows into and out of Lake Mission Viejo. Oso Creek then feeds into San Juan Creek which feeds into the ocean. Water is not the only thing carried into the ocean from these watersheds. There is also small particles of rocks that were taken from these hills and were dumped in the ocean in the form of erosion. The more it rains, the more erosion happens and the more cliffs grow and the rock is exposed.
Now that you are familiar with a watershed, we can now talk about the vulnerability of them. When it does rain, here in southern California we have runoff. For us, this can be very bad for numerous reasons. When it doesn't rain for months, our roadways, highways, and even lawns become storage houses for oil and pesticides. Both of these are bad if they contaminate the water for us and other animals. Why? Because they promote algal blooms. Algae naturally grows in lakes. If too much of it grows due to fertilizer, it can use up all the dissolved oxygen (DO) in a lake, killing literally everything in the lake, and the animals who depend on the food in the lake. This can even kill all the algae in the lake as once there is no more DO, everything will suffocate and die. Luckily, most plants living in watersheds act as a natural filter. Unfortunately, this isn't enough. We are producing more harmful toxins that could go into our waterways more than it can be naturally fixed. Pollution is a very hard thing to get rid of. You need a place to store it that won't harm us or the environment and 9.9 out of 10 this isn't what's happening. Most of the toxins are released airborne, so we and other animals breath them in and when it rains, the toxins come back to earth in our water as acid rain. Toxins can become airborne by aerosol canisters, spray paints, combustion engines, fires, and even volcanoes. Yes, natural geological forces on earth can even produce toxins that are harmful for us, especially watersheds.
What can we do to keep Lake Mission Viejo clear of these dangers? For one, there are already rules and regulation in place such as only electric motor boats are allowed and no dumping of livestock in the lake. What you can do is to find alternative ways to keep pests away from lawns and to lower the risk of transporting the toxins involuntarily. One way is to build a fence around a garden or have an electric shocker for bugs. These methods can significantly reduce the risk of Lake Mission Viejo being contaminated with toxins, and having to have to be closed forever. Luckily for us, this isn't the case and we can all use the lake, and it's resources responsibly.
Some precautions were taken into account when the lake was being constructed in the 1970's. Because ground water is extremely fragile and important, the lake was sealed with a clay cap. This not only helps contaminated lake water (if it did happen) from getting into our groundwater, but also helps keep the lake from literally drain into the ground and keep the evaporation rate low. There was also a drain near the south end of the lake that is underwater so if the lake needed to be drained for any reason, it could be done. You cannot see the drain unless you dive under water. If the drain would happen to be open, the water would drain into Oso Creek and eventually the ocean.
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS BEFORE YOU LOG A FIND. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
1. Lake Mission Viejo on the first line of your email.
2. As you walk from the parking lot in the waypoint section, look for any ancient sea shells in the sidewalk. Pick anyone you like and describe the (a) texture, (b) length in cm or in, (c) color, (d) shape AND (e) using the shell chart above, what depth would you estimate these shells to be found at?
3. Using the Lakeside Promenade Map, in your opinion, which area listed would be at the highest risk to contaminate the lake with fertilizer.
4. Using the Mission Viejo: The California Promise plaque, name at least one species AND how they could be affected in a negative if this event from the question above actually happened.
5. Describe current water quality of the lake AND your explanation as to why it's like this.
6. In your opinion, do you think the lake is shrinking, stagnate, or growing AND your explanation as to how you came to your conclusion.
Works Cited
http://articles.latimes.com/1991-07-30/news/mn-135_1_mission-viejo
http://www.detectingdesign.com/fossilrecord.html
http://www.socalwetlands.com/website/main.htm