[9] Originally settled in 1839 as Rancho Los Medanos, the area of almost 10,000 acres was issued to Californios Jose Antonio Mesa and his brother Jose Miguel under a Mexican Land Grant by then Governor Juan Bautista Alvarado, one of the final land grants issued prior to the formation of California as a state.

[12] General William Tecumseh Sherman laid out the first network of streets on the west side of town.

The area was the midway stopping point for schooners traveling from San Francisco to the gold country further inland.

Fishing, farming, and cattle raising for the hide and tallow industry were the major economic activities during this time.

[13] Steam powered engines moved coal cars down the tracks along present day Railroad Avenue to the waterfront docks that came to be called "Black Diamond Landing."

An industry was born with fishermen, packing plants, boat builders and the like dominating the local waterfront for the next 80 years.

The town boasted the largest Delta fishing community in the state, made up primarily of Sicilian immigrants, the families of which have remained in the area for generations.

In 1957, the State of California closed down the Sacramento Delta to commercial fishing, ending the area's industry.

Hooper purchased the land grant and gave birth to many manufacturing ventures, beginning in 1903 with the creation of the Industrial Center of the West.

[10] In 1903 the town was incorporated, and by a vote of the citizenry, was renamed "Black Diamond", after the mining firm.

[15] In 1918 the shipyard of the Pacific Coast Shipbuilding Company was built in neighboring Bay Point, the associated company town of Clyde, California alongside it, but as soon as the World War I shipbuilding boom was over, the yard was closed in 1921.

The Pittsburg plant continued to grow until the early 1950s, reaching a peak staff of 5,200 employees when the markets for its products crashed.

Together they invested $450 million turning the Pittsburg plant into a modern flat-products mill, renamed as USS-Posco.

As of 1999, the facility employed 970 workers and shipped over 1.6 million U.S. tons per year of steel to over 175 customers in the Western U. S., Mexico, Canada and the Pacific Rim.

[16] The original town site fronts on the Sacramento/San Joaquin River Delta, reflecting its origins as a deep water channel river port (As of January 1, 2007, state legislation [Assembly Bill 2324] enabled the city to manage its own riverfront for commercial development and subsequent port operations).

Since the early 1900s, the city has grown inland to the south, then spread east and west along State Route 4, now a freeway carrying resident commuters to jobs in the San Francisco Bay-Oakland Region.

USS-POSCO Industries (a joint venture between US Steel and POSCO of South Korea) and Corteva maintaining plants in Pittsburg.

[30][31] The California Theatre, opened in 1920, began as a venue for live vaudeville performances and silent films.

During its heyday, notable performers included Flash Gordon and cowboy heroes Ray “Crash” Corrigan, Tim Holt, Tex Ritter and Fred Scott.

Today, the auditorium features a 981-seat capacity, beaux-artes style ceiling decoration, and a grand balcony.