Turtle Rock is the name of a neighborhood in Irvine. But did you know it is named for an actual rock? Here, you'll see Turtle Rock a large limestone outcrop full of fossils and other interesting geologic features in the middle of a suburban neighborhood. The rock is protected by the city of Irvine due to its religious significance with the local Native Americans. Climbing the rock is prohibited, so please only make your observations from the ground.
The rock is made out of limestone which forms in a warm, shallow marine sea. Limestone is commonly found along the Southern California coast since much of the LA basin (which Irvine is apart of) was underwater around 5 million years ago. Limestone forms from the accumulation of calcium rich sediment, typically from dead organisms that have calcium carbonate shells. When they die, their bodies (along with their shells) sink to the sea floor. Over time, more accumulation occurs where the sediments can solidify into solid rock as the weight of sediments above compresses them. In addition tectonic forces can also compress the rock even harder.
Eventually, as the land rises due to shifting tectonic forces, the solid limestone is uplifted above sea level and is eventually (in some places) brought to the surface. In Orange County, limestone can be found in Laguna Canyon, parts of the Santa Ana Mountains, and of course right here in Irvine.
Turtle Rock, like most limestone formations, is susceptible to pitting. Pitting is a type of weathering feature that is a result of slightly acidic rain. Weathering is the breakdown of rocks while erosion is the transport of weathered material. Rain is naturally acidity (with a pH of around 5.6). The pH scale goes from 0 to 14, with numbers below 7 considered acidic and numbers above 7 considered basic. Exactly 7 is considered neutral. The rain can dissolve parts of the limestone and over time, can create pits or holes in the rock where the rain likes to collect. Turtle Rock has ample evidence of pitting.
Works Cited
https://commons.wikimedia.org/wiki/File:Garden_Cave_-_karst-pitted_limestone_wall_at_entrance_%28San_Salvador_Island,_Bahamas%29_2_%2816240307230%29.jpg
https://isgs.illinois.edu/outreach/geology-resources/pelecypods
https://www.epa.gov/acidrain/what-acid-rain
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. "Turtle Rock" 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 close up photo of your favorite fossil using some sort of scale. Geologist sometimes use coins, books, or even humans! Be creative in what you choose for your scale. Note: this is not a selfie, but rather a documentation of the geology using a scale. This photo must be uploaded to your "found it" log.
3. Describe the pelecypod fossils. Give a description of their relative (a) sizes, (b) abundances, (c) colors, (d) shapes, and (e) visable/textural features.
4. Based on your answer in number 3 (above), use the pelecypod chart in this cache page to identify the specific type of pelecypod that is most abundant here.
5. Describe the pitting. How is this weathering feature is effecting Turtle Rock AND explain why this is occurring.