Welcome to Sunset Cliffs! This area has tons of opportunities for surfing, sunbathing, or even just walking in the sea breeze.
At the posted coordinates, you’ll be able to see two kinds of rock:
The “Bay Point” Pleistocene sandstone formation is estimated to be 120,000 years old. It is the yellowish rock that forms the cliffs here.
The “Point Loma” Cretaceous shales and silts are the brownish-gray rock you see further down. This formation is estimated to be 75 million years old.
At this beach, which you can view from where you are standing up on the cliff, the Point Loma formation is openly exposed with lots of texture on display. You may see surfers wading out onto this submerged rock platform to catch a wave. This section of rock in the water right by the sand is the intertidal zone. Further on, it leads to the seafloor and creates platforms and reefs which buffer against the waves and lessen their impact on the shore.
Shale is composed of clay and silt, so it has plate-shaped particles that lie flat when deposited in water. Unlike sandstone, shale does not tend to form thick layers. Instead, it forms thin, sheet-like layers, influenced by the flat particles. (The shale splits along the original planes of the particles.) This beach contains visible evidence of this shale layering, showing how sediment accumulated over time.
Sources: Sunset Cliffs Natural Park Council, "Find Gemstone" mineral article database
To log the cache, answer the following questions:
-Describe the various colors, textures, types of features, etc. of the “Point Loma” formation in the water by the beach. Do you see any shale structures sticking out, and if so, what do they look like?
-What are some ways the shale layer in the water looks different from the sandstone layer on the cliffs? Describe how the color, texture, type of features, etc. are not the same.
-Describe what the intertidal zone looks like: does it aggressively drop off toward the sea floor or is it more of a gradual slope?
-Do you see an example of how shale stacks in flat, accumulated layers? If so, describe it and its location, or enclose a picture if possible.
-Looking at the same section of shale, how are the layers stacked? Do they look like layers on a cake, with each layer being around the same size and evenly stacked…or are they more uneven, with parts of it stacking neatly but other parts sticking out of the stack?
-Do you think the rock formations have any effect on the waves? If so, describe what you see.