The ground you stand on and the lake before you are what remains of Bilger quarry, which opened in 1870 started mining “Blue Rock”, which is actually metamorphosed sandstone with lime carbonate in its seams. The mineral would be crushed and become part of the pavement in the streets of Oakland for many more years.
Metamorphosed sandstone comes from mountain- building events in convergent plate boundaries. The Sandstone is the metamorphosed into quartzite when it is deeply buried. Extreame Compression forces in the plate boundary fold and fault the rocks, and thick the crust into a mountain range.
Quartzite is a Ridge- Former. Its one of the most physically and chemically restart rocks found on the Earth’s surface. Thats why its frequently found in the mountains. When mountain ranges are worn down by weathering and erosion, the less resistant and less durable rocks are destroyed. leaving only the Quartzite.
Feel free to log the smiley. Email or geo-message me the following answers:
- the GC code or name of the geocache
- how many big blue rocks are within 20ft of the Earthcache?
- What dose the blue rock feel like, compared to the red?
- do you see more quart deposits in the blue or red rock?
