$15,000,000." Personal life He is considered to have been one of the 100 wealthiest Americans, having left an enormous fortune. He died of Bright's disease on May 2, 1878 in San Rafael, California. He was buried at Calvary Cemetery in San Francisco which eventually closed, his remains were moved to Holy Cross Cemetery in Colma, California. The design plans for O'Brien's memorial at Calvary Cemetery can be found at U.C. Berkeley's Bancroft Library. References External links 1825 births 1878 deaths American investors American stockbrokers Irish emigrants to the United States (before 1923) People from County Laois American mining businesspeople 19th-century Irish people 19th-century American businesspeople Burials at Calvary Cemetery (San Francisco, California) Burials at Holy Cross Cemetery (Colma, California)