The Town of Bonanza is a Statutory Town located in Saguache County, Colorado, United States. Formerly known as Bonanza City, Bonanza is a largely abandoned former silver mining town. Bonanza is a Spanish language word meaning prosperity. The town population was 16 at the 2010 United States Census, ranking Bonanza as the second least populous municipality in the State of Colorado. The Villa Grove Post Office now serves Bonanza.