Teacher’s Day at Black Diamond Mines Regional Preserve Celebrates Earth Science Week

Ray Sullivan, San Francisco State University, and Christie Johnson, East Bay Regional Park District—October 13, 2001

By Dan Day, from the November 2001 NCGS newsletter

The East Bay Regional Park District (EBRPD) and the NCGS hosted Teacher’s Day at Black Diamond Mines on October 13th. This function celebrates Earth Science Week by allowing Bay Area K-12 earth science instructors an opportunity to learn about the geological, biological, and historical aspects of coal and sand mines operated there during the late 19th through mid-20th century.

The program started at 9:00 a.m. in the HazelAtlas Mine meeting room, where Dr. Ray Sullivan of San Francisco State University spoke on the geological history of the area. Ray and his students have spent many years characterizing the geology and interpreting the paleogeography of this site. The geological history began with the Jurassic breakup of Gondwanaland. Ensuing nearshore sedimentation created the most important deposit with regards to historical mining operations, the Eocene Domengine Sandstone. This unit was laid down about 50 m.y. ago (more precise fossil evidence yields an age of 49.5 Ma). The overall plate tectonic picture at this time indicates an active subduction zone was off the coast; present-day San Francisco would be located in the trench at that time. Based on paleobotanical evidence, the climate was tropical at this time and the Central Valley was part of a broad continental shelf. Ray’s detailed paleoenvironmental reconstructions indicate that the Domengine was deposited in an estuary complex that bordered the Sierra foothills and extended north to the Sutter Buttes from a point east of Sacramento. Hence the entire Sacramento Valley was estuarine and separated from the San Joaquin Valley by the prominent Stockton Arch. Concord now lies where the continental slope at that time began. The 6,000- to 7,000-foot-deep Meganos submarine canyon passed seaward through the Mount Diablo area. The Domengine contains two lignite-grade coal seams and an abundance of glass-grade sand, both of which supported mining operations during the late-1800s and mid-1900s. The Domengine is conformably overlain by the Norton Shale, which in turn is capped by the Markley Formation, containing deepwater sands and mudstones. This succession records a sudden deepening of the shelf.

To illustrate his interpretations, Ray showed the group a series of slides depicting modern-day estuarine conditions in San Francisco Bay and the Bay of Fundy in New Brunswick, Canada. Examples included the sands of the subtidal zone, sands and muds of the intratidal zone, and muds/vegetation (coal precursors) of the supratidal zone. The Bay of Fundy, where the world’s largest tides occur, showed excellent high-energy crossbedded sands and other flood/ebb tide bedforms. Ray contrasted these processes with similar features taken from the tunnel walls at the Black Diamond Mines. A key piece of evidence denoting estuarine conditions in the Domengine sands are thin mud seams draped over sandy ripples that formed when clay settled out of the water at slack tide. This juxtaposition of drastically different energy conditions and sediment grain sizes occurs only under estuarine conditions. Trace fossil evidence includes Ophiamorpha shrimp burrows and other bioturbation-induced paleoenvironmental indicators.

Ray is a native of Wales, a major coal-mining district in Great Britain. He closed with slides depicting coal mining techniques and working conditions in his homeland, various coal processing technologies, and major disasters linked with the Welsh coal industry. He compared Welsh mining systems with those used at Black Diamond Mines, and noted the Welsh cultural influences.

The Black Diamond mining district evolved because it was the sole source of coal on the West Coast of America at that time. It was a poor quality lignite grade that occurred in two seams only a few feet thick. But the mines produced over 4 million tons of coal over a 40-year period before access to higher grade sources in South America and the state of Washington forced them to close down. During peak producing years, Black Diamond Mines coal was transported by train to docks at Pittsburg and then shipped to consumers in Stockton, Sacramento, and San Francisco.

EBRPD naturalist Christie Johnson followed Ray’s presentation with an account of the local history. The area was originally inhabited by Miwok Indian tribes. However, after 1772 Spanish, Mexican, and American settlers began arriving in the area. Cattle ranching was the major industry until coal was discovered. Coal mining began in earnest in the 1850s and was a major fuel source for San Francisco, Stockton, and Sacramento. Coal fueled the growing railroad system and heated homes and businesses. The Preserve is underlain by about 200 miles of tunnels, all of which have been closed for public safety. However the “Coal Rush” drew hundreds of people of Irish, Italian, French, German, Canadian, and Australian descent to the area. But most of the miners were Welsh. The cities of Nortonville, Somerville, Stewartsville, West Hartley, and Judsonville quikly sprang up. Because they were isolated by the rugged terrane, the towns developed a tight-knit social life. Dances and other events were held at the local hotels, the towns had many saloons, and baseball became a favorite recreational pastime. Unfortunately, the risks of mining left their mark on the people’s lives. Mine gas explosions and cave-ins claimed many lives, fires razed several buildings, and childhood diseases killed offspring in many families. Young boys labored in the mines and were subject to the same risks as the adults. The hearty townsfolk accepted these burdens as part of their livelihood and continued to work the mines. Ultimately the best coal seams were mined out and the operations were moved to Washington State. With the main source of income gone, the towns were eventually deserted. Many of the abandoned buildings were scavenged for lumber and parts as ranchers, some of them former miners, settled in the hills. In the 1920s Marvin Greathouse reopened the Somerville mine site to excavate sand for the Hazel-Atlas Glass Company in Oakland. The mines were worked until competition from Belgian sand used as ship ballast provided a cheaper raw material source. Another mine in Nortonville produced foundry sand for the Columbia Steel Works. It, too, closed when the foundry was shut down, and sand mining ceased by 1949. Both mines produced over 1.8 million tons of sand.

After Christie’s talk, EBRPD mining engineer Pat Dedmon led groups on a tour of the mine, pointing out mining and geological features to the teachers as they weaved their way through the well-maintained drifts. This tunnel system was opened to the public only a few years ago after extensive refurbishment was completed by staff member John Waters and his crew. This facility is the only maintained public mine in the Bay Area. It offers a first-hand glimpse of a major mining operation and a well-kept museum that catalogues the history and wildlife of this important coal-producing district.

After a delicious barbecue prepared by the now legendary NCGS Past President Tridib Guha and his assistants Phil Reed and Dan Day, Christie took the group to nearby Rose Hill Cemetery. This site was where the locals were buried. It also provides clues to the history of the settlements, of personal relationships, and clues to the cultural evolution of the area. The gravestones themselves tell a unique story. The oldest markers were carved from marble, which weathered poorly in the acidic soil. The discovery of techniques to carve the hard granite and gabbro rock slabs quarried in the Sierra foothills saw these rock types replace the less resistant marble headstones. Many markers have suffered from acts of vandalism over the years. Now they are protected by the EBRPD. Christie led an exercise to glean historical information from the tombstones using newspaper clippings and obituaries from the time. Regional Parks staff member Tracy Parent is currently researching historical details about the settlements from newspaper archives. Her outstanding effort, which includes interviews with survivors from the mining settlements, has been a major contribution to the local history.

The annual Teacher’s Day event is a joint effort by EBRPD staff members at Black Diamond Mines Preserve and NCGS volunteers. Much of the preparation and presentation was accomplished by Regional Parks staff under the guidance of Naturalists Bob Kanagaki and Christie Johnson. Pat Dedmon conducted the mining tours and provided his technical expertise on mine construction, operation, and the geological features exposed in the mine tunnels. Dr. Ray Sullivan’s continued support of this event is instrumental in making it a success (not to mention his wife Barbara’s delicious Welsh cakes!). NCGS Past President Tridib Guha and his wife Mita always draw compliments for their excellent barbecue eats. And other assorted duties were tackled by 2001-2002 President Randy Kirby, Past President Don Lewis, Treasurer Phil Reed, and Newsletter editor Dan Day. We all look forward to next year’s event!