Example of a Ralston Purina hero medal, similar to the one awarded to Rivera. Bronze, 37mm. Front: Female figure placing a laurel wreath on a kneeling male; For Service to Others / Ralston Purina Hero Medal. Back: Hero Medal Awarded To / (Recipient's name and date on scroll) / By Ralston Purina Hero Commission / St. Louis, Mo. Examples are known to have been awarded as early as 1915 to children for lifesaving. Click to enlarge.

Silent film star William S. Hart (left) and Presbyterian minister Wolcott Evans (right), both of Newhall, pin a hero's medal on Louis Rivera in the aftermath of the St. Francis Dam disaster of March 12-13, 1928.

Dam researcher Ann Stansell writes (2014): Louis was the son of Joseph Peter Rivera and Addie M. (LeBrun). Both were lost in the disaster, as were two siblings, William and Albert. Louis was given the award for saving the lives of his two sisters, Mary and Belle. According to the Newhall Signal, May 24, 1928, a hero medal was given to Louis by Hart on behalf of the Ralston Purina Hero Fund.

Construction on the 600-foot-long, 185-foot-high St. Francis Dam started in August 1924. With a 12.5-billion-gallon capacity, the reservoir began to fill with water on March 1, 1926. It was completed two months later.

At 11:57:30 p.m. on March 12, 1928, the dam failed, sending a 180-foot-high wall of water crashing down San Francisquito Canyon. An estimated 411 people lay dead by the time the floodwaters reached the Pacific Ocean south of Ventura 5½ hours later.

It was the second-worst disaster in California history, after the great San Francisco earthquake and fire of 1906, in terms of lives lost — and America's worst civil engineering failure of the 20th Century.