Black Diamond Regional Mines Preserve Reopens Visitor Center

The Greathouse Portal Visitor Center, inside the former Hazel-Atlas sand mine, is open again after five years. Photos by Andrew Alden

The Greathouse Portal Visitor Center, inside the former Hazel-Atlas sand mine, is open again after five years. Photos by Andrew Alden

With California’s state parks under threat of imminent closure, the East Bay Regional Park District is a bright spot for naturegoers. Careful management has maintained steady funding in hard times, and this summer EBRPD’s Black Diamond Mines Regional Preserve promises to be a well-attended place—especially with the long-awaited reopening of its underground Greathouse Visitor Center.

Black Diamond is named for its history as California’s largest coal district, starting in the 1850s. Coal was a prerequisite of 19th-century technology, and its discovery in the hills south of Antioch helped propel the new state of California to prosperity. It wasn’t great coal, being classified as lignite or the lowest grade of coal, but it was good enough to do the job. Several mining towns sprang up here, and for a while this was the biggest settlement in Contra Costa County.

Fragments of Black Diamond's low-grade lignite coal can still be found in the tailings piles.

The coal didn’t run out, but by the 1890s better coal was available from elsewhere so the mines shut down soon after. Next came the exploitation of the premium quartz sand beds beneath the coal. The sand mines supplied glassmakers in Oakland and steelmakers in Pittsburg from the 1920s to the late 1940s. That was when the Greathouse underground chamber was created, in the Hazel-Atlas sand mine. The Regional Parks District repurposed it as a visitor center in the 1970s, but storm damage shut it down in 2007. After five years of painstaking rehab, the room is receiving visitors again every weekend at no charge.

The old mining district is hidden from the riverside sprawl of Antioch behind a narrow canyon and oak-dotted hills. Driving through the canyon is like leaving the 21st century behind.

Inside, the vegetation is more lush on the higher hills, and miles of trails snake through the country. The area is notable for wildlife and plant species, but geologists find it notable too.

The bones of the hills are relatively young sedimentary rocks that are well exposed here. They extend all the way across the Central Valley in the subsurface. I look forward to showing you more as I explore this beautiful place.

Black Diamond Regional Mines Preserve Reopens Visitor Center 17 May,2012Andrew Alden


Andrew Alden

Andrew Alden earned his geology degree at the University of New Hampshire and moved back to the Bay Area to work at the U.S. Geological Survey for six years. He has written on geology for since its founding in 1997. In 2007, he started the Oakland Geology blog, which won recognition as "Best of the East Bay" from the East Bay Express in 2010. In writing about geology in the Bay Area and surroundings, he hopes to share some of the useful and pleasurable insights that geologists give us—not just facts about the deep past, but an attitude that might be called the deep present.

Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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