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Peering a few feet within the Hazel Atlas Portal at the Black Diamond Mines Regional Preserve south of Antioch, California. The area was rich in production of silica sand & coal (the Mount Diablo coal field being discovered in 1855). During its heyday, the area had 12 mines that supported thousands of miners and their families from around the world in five town sites. Four million tons of sub-bituminous and lignite coal was extracted from the Mount Diablo coal fields until the quantity, price and quality was overtaken by a larger operation with higher-quality anthracite coal from Washington State. The townsites were abandoned and houses moved when the mines closed around 1906.
In the 1920s, a mine producing high-quality silica sandstone was started by owner Marvin Greathouse on a hillside above the Somersville townsite. He sold the product to the Hazel-Atlas Glass Company which operated a plant in Oakland manufacturing glass containers. Hazel-Atlas eventually purchased the mine and operated it until about 1945.
From: https://www.kqed.org/science/23430/bay-areas-coal-mining-history-at-the-black-diamond-mines-regional-preserve
https://en.wikipedia.org/wiki/Black_Diamond_Mines_Regional_Preserve
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The Bay Area is renowned for its natural beauty, affluence, diversity, and progressive thinking new age reputation. Lots of ammenities, tours and hotels can be found all around the area.San Francisco is the cultural and financial center of the Bay Area, and has the second highest population density of any major city in North America after New York City. It is also a major tourist destination, and transport and accommodation is plentiful, ranging from luxury hotels to cheap accommodation. San Jose is the largest city in terms of population, land area, and industrial development, and is the center of Silicon Valley, a well-known high technology region. Oakland is a major manufacturing and distribution center, rail terminus/hub, and has the fourth largest container shipping port in the United States.Largely because of San Francisco and Silicon Valley, the Bay Area presently ranks second only to the much larger New York City region in number of Fortune 500 company headquarters (April 2010 Fortune Magazine). source: wikipedia