The top of the world, as it is called, offers incredible views of the Pacific and Orange County in general. Top of the world also offers a unique opportunity to learn about joints. In geology, joints refers to regular and angular cracks in a rock (photo below). This occurs due to a number of factors, but typically has to do with the way the rock formed and its mineral composition.
The type of rock located here is more commonly know as sandstone. More specifically, this sandstone formed in a shallow marine environment close to the shore. Sandstone is formed in a high velocity environment where sand particles are dropped out of suspension and fall to the ocean floor. Over time, more sand overlays previous particles. Due to the weight of these layers, the sand can compress, and compact. Depending on mineral infiltration (which can act as a sort of cement which holds the grains together), time, and pressure of the sand above, the sandstone can be well or poorly compacted.
Interestingly, this specific outcrop of sandstone is not associated with the Monterey Formation, which is found in most of Southern California's coastal regions included most of Laguna Canyon. According to a 1965 state geological survey map of the area, this sandstone formed as a result of marine terracing and uplifting. The highest parts of Laguna canyon contain these beach like deposits, about a few hundred feet or so above sea level. Everything below these thin beach deposits (meaning anything that is older) is part of the Monterey Formation.
This sandstone is loosely compacted which is why it is jointed. Joints normally occur as a byproduct of weathering. As a rock weathers away, it typically does along cleavage or weaknees within its crystal structure. The angle of the joints can provide some information as to the rock type and what minerals are present. Joints can also form as rocks are uplifted and depressurized. In other words, as rocks are brought up to the surface, they are exposed to lower pressures than where they formed deep within the earth. This allows the solid rock to expand and joint (crack) along predictable angles. This is a common occurrence in Yosemite National Park as granite is brought up to the surface, where it joints and exfoliates into small sheets that slide off one another.
Works Cited
https://structuralgeo.wordpress.com/2014/06/18/jointing-and-mechanical-layering/
https://www.conservation.ca.gov/cgs/Documents/Publications/Geologic-Atlas-Maps/GAM_019-Map-1965.pdf
https://www.conservation.ca.gov/cgs/Pages/Program-RGMP/regional-geologic-maps.aspx
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL THE QUESTIONS BELOW. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER TO SEND YOUR ANSWERS. ANY INCORRECT ANSWERS MAY RESULT IN A CLARIFICATION RESPONSE FROM ME.
1. "Joints at the Top of the World" 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.
2. Take a close up photo of the joints using some sort of scale. Geologists often use coins, GPS', pens, shoes, notebooks, ect. You might want to be creative in what you use for your scale, however, the scale that you choose is entirely up to you. Make sure your photo is close enough to capture joints that can be clearly seen. This photo must be uploaded to your log. Do NOT send me photos with your answers.
3. Estimate the angle in which these joints intersect.
4. Describe the colors, textures, and grain compaction of the sandstone. Is it poorly compacted, well compacted, or somewhere in the middle?
5. Describe any weathering that is occurring. Is there rusting or corrosion? If so, where do you see it and why is it occurring? Explain
6. Describe the regular spacing between joints AND give an estimate of the average distance between joints.