Discover Mission Viejo Geotour
This cache is part of the official “Discover Mission Viejo GeoTour GT4D8” which will lead visitors to discover trails, parks, and other prominent locations throughout Mission Viejo. Those who complete the tour will be eligible to receive a GeoCoin for their achievement by completing the GeoTour passport and finding code words. Passports and instructions can be found here: Geocaching | City of Mission Viejo.
Calico Canyon is one of Mission Viejo's most hidden gems. It was formed by erosion from the Oso Creek and its tributaries. Much of the creek is flowing year-round in part due to runoff which can cause environmental hazards. This earthcache, however, will focus on the geology of Calico Canyon such as what the canyon is made of and how erosion sculpted the canyon into what we see today.
The materials that form the canyon walls were formed in the last 5 million years in the late Quaternary. During that time, much of this area was under ocean water. Sediments from nearby rivers would flow into this water and settle out, eventually forming sandstone and mudstones. This is what we see today along the modern Southern California coast, known as the Monterey Formation. Among these layers, there are plenty of marine fossils. Some of the largest include baleen whales and megalodons, however there are a plethora of smaller fossils such as clams and occasionally fish.
Over the last several million years, this rather loose material was compressed, compacted, and heated to form hard, solid rock. It all is related to plate tectonics of the region, which have been uplifting the coastal areas of Southern California for the last few million years. With increased uplift comes increase erosion. Since being uplifted above sea level, rain and natural runoff have sculptured this canyon by weathering down the rock and eroding it downstream.
Sandstone and mudstone erode at different rates. Sandstone is more resistant to mudstone and therefore will tend to literally stick out adjacent to mudstone. You can see this clearly in the image below. Additionally, the rate of erosion is dependent on the topography which itself depends on the geomorphology and tectonics of the region. As the land uplifts it creates gradients that water can flow down which, through time, form larger and larger channels and eventually a canyon, like the Grand Canyon is sculpted into the landscape. The steepest gradient is found furthest away from the mouth and ocean, in the mountains and hills. Here, the erosion rates are highest since the downflowing water has the highest velocities. This makes sense as most streams originate in mountains or hills and as the water flows closer to the ocean, where topography is more gentle, erosion occurs less and deposition occurs more.
Deposition occurs for different particle sizes at different flow rates. This depends on the grain size of the particle. For example, sandstone will settle out before siltstone as sand particles are larger (more massive and heavier) than silt particles. That said, the larger the clast size, the more energy is required to transport them downstream. So by looking at the clasts sizes of a river or stream, one can determine the relative flow rate (or discharge) of a stream at any particular point along its path.
Traction is the movement of particles that are not suspended as they move downstream. In essence, large rocks roll! This occurs to clasts that are quite big and heavy where they cannont become suspended in the river. Through time, they weather and tend to be more round as distance from where the rock originate from increases. This implies if they are jagged and angular, then they are close to their source. However, smaller particles can become suspended in the water if flow is high enough. Particles like clay, sand, and pebbles become suspended at different discharge rates.
Clay sized particles become suspended at lower discharge rates than sand. Sand sized particles become suspended at lower discharge rates than gravel, and so on. As discharge rates increase, so does the grain size of rocks that can be carried by it. The more discharge, the more force, which implies the larger an object can be before it is moved by the river.
In very rare circumstances, floods can occur. Floods carry all types of grain sizes from clay to boulders. When flood waters recede, they leave behind a rim or berm of material, typically large and coarse (angular, not smooth). This can be seen in a landscape if a flood has occurred recently or, through time, this is errored and any record of a flood occurring has been diminished. Luckily for the residents of Mission Viejo, this part of Oso Creek rarely floods even during high rain fall events (inch per hour). It's good that no homes are located within this canyon!
How to get the code word for this cache to complete the DMV Passport
Because earthcaches have no physical container it is not possible to place a physical code word at the posted coordinates. Instead, to get the code word for the passport, you must find a historical marker near GZ (see waypoint section for exact coordinates). It discusses the history of this sculpture, which represents the local geology. Enter the name of the sculpture (two words) into certitude below and if correct, the code word for this earthcache will be given in the "Bonus Info" section. This code word can be recorded in your official Discover Mission Viejo Passport. Note the name of the sculpture is NOT the code word. Also note that this is NOT required to log this earthcache as a find. This is optional for those who want to be eligible for the geocoin.
You can validate your code word with
certitude.
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL OF THE QUESTIONS BELOW. You can contact me through the geocaching message center or email to submit your answers. Any incorrect answers may result in a clarification response.
1. "DMV 6 - Calico Canyon" on the first line of your message 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 spirit of earthcaching.
2. Take a photo of you (or you signature item if you don't want your face to be shown) on the bridge with the canyon in the background. This photo MUST be uploaded to your "found it" log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
3. From the vantage point along the bridge, look at the rocks that make up Oso Creek and Calico Canyon. Describe the (a) grainsizes, (b) roundness and shapes, (c) colors, and (d) relative abundance. Also, (e) do you think these rocks are sourced locally or were transported from far away?
4. Describe the discharge rate of the creek. Is the flow relatively high, low, or stagnate? What does that tell you about the erosion rates?
5. Using your answers from questions 3 and 4, are these clasts primary transported by traction, suspension, saltation, or solution? How can you tell?
6. Do you see any evidence of storm deposits? If so, where and describe what they look like. If not, explain why you may not see them.
7. Describe what you might expect to see in Calico Canyon if Oso Creek experience a flood event today.
Works Cited
https://pubs.usgs.gov/of/2006/1217/of2006-1217_map/of2006-1217_geol_map.pdf
https://www.sdge.com/sites/default/files/4.6_Geology%2520Soils%2520and%2520Mineral%2520Resources_0.pdf
https://ngmdb.usgs.gov/Prodesc/proddesc_409.htm
https://www.istockphoto.com/vector/formation-of-sedimentary-rocks-gm1341803189-421421210
http://chubbyrevision.weebly.com/river-landforms.html
https://www.sciencefacts.net/sedimentary-rocks.html
https://link.springer.com/referenceworkentry/10.1007/978-1-4020-4409-0_18
This cache has been placed with special permission from the City of Mission Viejo and Geocaching HQ.
Cache was placed, designed, and maintained by bluesnote