wow look at this rock let's look into how it formed, Differential Erosion is the process where some parts of a rock wear away faster than others. This isn't random; it happens because rocks are rarely uniform. Think of a boulder like a loaf of "fruit bread"—the dough is soft, but the nuts and raisins are hard. If you rained water on that bread, the dough would wash away, leaving the nuts perched on tiny stalks.
In the geological world, this "uneven wearing" is caused by three main factors:
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Mineral Hardness: A rock might be a mix of soft calcite and hard quartz. The quartz stays while the calcite dissolves.
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Cementation: In sedimentary rocks, the "glue" (cement) holding grains together can be stronger in some spots (due to silica) and weaker in others (due to clay).
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Chemical Resistance: Some minerals react chemically with rainwater (which is slightly acidic), causing them to "melt" away faster than non-reactive minerals.
The "Mushroom" Effect (Pedestal Formation)
The small mushroom shapes you see on this boulder are miniature versions of Hoodoos (like those found in Bryce Canyon utah). Here is how they formed:
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The Protective Cap: A small area on the surface—perhaps a pebble embedded in the rock or a patch of harder mineral—acts as a "shield."
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Vertical Erosion: Rain strikes the boulder. The water washes away the softer material surrounding the "shield."
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The Stem: As the surrounding surface lowers, the "shield" protects the rock directly beneath it. Over time, this protected column becomes a "stem," while the shield becomes the "cap" of the mushroom.
Because this boulder is near a sidewalk, urban hydrology also plays a role. Splash-back from the pavement and concentrated runoff from the sidewalk can accelerate the erosion on the sides of the boulder, making these shapes even more pronounced.
To claim this find, please message the CO (Cache Owner) the answers to these questions:
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Observation: Look at the "caps" of the small mushrooms. Do they look like a different material (color/texture) than the "stems," or are they just the same rock that happened to be protected?
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Measurements: Find the most prominent "mushroom." What is the diameter of the cap versus the diameter of the stem?
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Hydrology: Look at the sidewalk and the boulder's position. Does it look like water pours off the sidewalk onto this specific spot, or is the erosion coming solely from direct rainfall?
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Comparison: Find a part of the boulder that is smooth. Why do you think mushrooms didn't form there? (ex: Is the rock more uniform in that spot?)
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