The term Bonanza Group, together with the names "Big Four" and the "Irish Four," refers to a group of immigrants who outmaneuvered William Sharon and broke the monopoly of his Bank of California until they controlled much of the Comstock Lode. Two Irish miners, John Mackay and James Fair, with the financial help of James Flood and William O'Brien, San Francisco investors, seized control of Virginia City's Hale and Norcross Mine in 1869.   

           

The four men then aggressively obtained other claims. In 1873, while exploring the Consolidated Virginia and California Mine, Fair and Mackay discovered an astonishingly rich ore body eventually known as the Big Bonanza. Phenomenal profits made Mackay, who owned two-fifths of the partnership, one of the richest men in the world. He and his associates formed the Bank of Nevada to rival Sharon's institution. 

 

The Bonanza Group controlled most of the Comstock Lode throughout the rest of the nineteenth century.