From the Wikipedia: The Black Diamond Coal Mining Company was formed in 1861, consolidating the Cumberland and Black Diamond coal mines in the region of Mount Diablo, in Contra Costa County, California. During its years of operation as a mining company, it established three towns: Nortonville , California, Southport , Oregon, Black Diamond and Franklin Washington. The company's mines in California and its settlement of Nortonville later became part of the Black Diamond Mines Regional Park and a California Historical Landmark. Several railroad lines were built in California and Washington to support the company's mines, and the company operated numerous ships to transport its coal. As the mines played out and petroleum became the more common source of energy, the company closed its mines and transitioned into real estate as the Southport Land and Commercial Company.
The Mt Diablo Coalfield played a vital role in the early development of San Francisco and the Bay area. More than a hundred miles of underground tunnels were dug and the coalfield produced 4 million tons of coal valued at twenty million dollars. The mines produced low grade, sub-bituminous or lignite coal but for a while they were the only local supply in Northern California so their importance can hardly be exaggerated. Five towns grew up around the pitheads; Nortonville, Somersville, Judsonville, Stewartville and West Hartley. Although nothing remains of these settlements today, at least two of them, Nortonville and Somersville, were home to thriving Welsh communities in the late 19th century.
Noah Norton founded Nortonville in 1855 and, along with his three partners (Cutler, Matheson and Sturgis) started the Black Diamond coal mine in 1860.
The town grew to a peak population of approximately 1000 and was home to many Welsh miners. A cursory examination of burials in Rose Hill Cemetery reveals many Evans's, Jones's and Griffith's amongst those interred (See: Individuals Interred in Rose Hill Cemetery ). In the course of listing prominent Welshmen settled in the San Francisco area the Rev R.D. Thomas in his Hanes Cymru America 1872 , notes that - "The Rev J. Pryse is in Nortonville with the English Congregationalists." Other prominent early Welsh settlers include Morgan Morgans who emigrated from Wales to Pennsylvania in 1846. He moved to Nortonville in 1868 and began his association with the Black Diamond Coal Company in that year. Morgans moved north and became Superintendent of Mines when the company set up operations in Black Diamond, Washington in 1882. As such he exerted authority and control over almost every aspect of town life. He became a wealthy man and retired in 1904. For more on Morgan Morgans, whose career spans much of the history of the Black Diamond Coal Mining Company, see this excellent article on History Link - Morgans, Morgan (1830 - 1905)
There was a post office in Nortonville between 1874 and 1910. It closed temporarily in 1887 and again between 1890 and 1891. The town also boasted its own railway line which ran north for six miles to a terminus at Black Diamond Landing on the San Joaquin river, near present day Pittsburg. Opened in 1868, the line operated until the closure of the Nortonville mines.
The company closed its mines in 1885 due to a combination of low quality coal and drainage issues. Most of its employees were relocated to Southport, Oregon and Black Diamond, Washington.
Nortonville today is an eerily beautiful and deserted area which is administered as a regional preserve by the East Bay Regional Park District. There are scant remains of the old pit workings and nothing of the town itself. Rose Hill Cemetery preserves many of the graves of the former inhabitants, prominent amongst them, Sarah Norton, wife of founder Noah Norton. Sarah Norton was also the towns' midwife. She delivered over 600 babies in the course of her career and died in a tragic buggy accident in 1879 at the age of 68 years. Her ghost is said to haunt the cemetery.
The modern day Black Diamond Mines Regional Preserve comprises 8,533 acres and most of the former mining area lies within its boundaries. There are many trails through the park and it is a superb location for hiking and picnicking. There are two visitors centers, one of which, the Greathouse Center is named after the former Greathouse coal mine. There are a number of fascinating wall panels depicting the history of mining in the area which can also be seen on the centers' website here:- Interpretive Brochures & Panels | Black Diamond Mines
It should also be noted that mining made something of a comeback in the 20's and 30's with the opening of the Hazel Atlas Sand Mine. The mine supplied sand used in glass making by the Hazel-Atlas Glass Company in Oakland. Situated in the park not far from Nortonville, this mine is open for underground tours on weekends from March through November. None of the former coalmines are similarly accessible for obvious reasons. They are very old and unstable, largely flooded and only accessible via deep vertical shafts rather than inclines or adits.