Tourism and real estate: Toward the end of the 1920s, investors recognized the potential to develop a tourism and entertainment area along the Los Alamitos Creek. In 1927, while mining continued up on the hill, brothers George and David Black acquired the Casa Grande and opened its first two floors to businesses while living on the third floor. After installing several swimming pools in the backyard, they opened Club Almaden, a summer resort. Ben Black — a bandleader, banjo player, pianist and as a songwriter — had separately purchased surrounding mining company land at the Hacienda and subdivided it, bringing the latest entertainment culture to the quiet former mining village. The Casa Grande also served at various times as a post office, restaurant, and theater. David Black added a raised outdoor dance floor off the north side of the building in 1931. The main floor was leased to a restaurant that served as the social heart of the club through World War II. The outdoor dance floor was later enclosed to become a ballroom that would become a live theater known as the Opry House, which hosted vaudeville acts and community plays.
One town, two worlds: While the "Club Almaden" era brought a new festive energy to the valley floor along the creek, the hills remained mining territory, especially with the onset of World War II, which triggered a federally-backed revival of the mines to meet military demand for mercury. The following years saw a strange collision of worlds in the area: while visitors danced at the Opry House or swam in the Black brothers' pools at the Hacienda, industrial trucks rumbled past. At this time the miners and the resort guests were often the same people—local families who had stayed in the area after the 1912 closure. As the era of profitable mining finally reached its end in 1971, the New Idria Mining and Chemical Company that had acquired the New Almaden property was sitting on over 4,000 acres of land that was becoming a tax and liability burden.
Houses or trails: Because of its proximity to the growing tech hub of San Jose, developers eyed the hills for luxury estates and the chance that it would be sold to them was high. This possibility sparked a "Save the Quicksilver" movement among local historians and conservationists who argued that the land's unique mining history and delicate ecosystem deserved protection. The area was saved by the 1972 County Park Bond Act, where Santa Clara County voters approved a measure that provided the funds specifically for land acquisition to create a "greenbelt" around the valley. New Almaden was the "crown jewel" of this acquisition strategy because of its size and historical significance.
County purchase: Santa Clara County officially purchased the core mining property from the New Idria Mining and Chemical Company for roughly $3.5 million in 1975. The purchase included the mining rights, the historic structures, and the massive network of underground tunnels. Shortly after, the county acquired the Casa Grande and the surrounding Hacienda land, reuniting the mining hills and the tourist area for the first time in many years.
Finaly a park: The county still had a great deal of work to do before the lands could be opened to the public. From 1975 to 1976, a massive clean up took place. Hundreds of open vertical shafts and "glory holes" had to be sealed with concrete or heavy steel grates. Then there had to be a long-term study of mercury levels in the soil and water, which continues to this day. The park officially opened to the public in 1976, coinciding with the U.S. Bicentennial, and today the Casa Grande is a museum covering the history of the mines and towns on the hill.