pdq, that sent me Googling, and I came on this blog post: A Rare 78 RPM Record about the St. Francis Dam Disaster, which includes a link to an mp3 of "The Breaking of the St. Francis Dam", a disaster ballad in the old style, sung by Edd Rice (Vocalion 5216), recorded April 5, 1982, according to this listing at Google Books. The disaster was on March 12, so that's quick work.

The blog is from John Nichols who apparently has a fine collection of St. Francis Dam disaster memorabilia, as well as a collection of 78s. In a comment below the post, he says, "I have lyrics to another song sung in Spanish about the disaster. It's a corrido. I heard one story about a man who was so broken up about the loss of him family members that he had to write what he needed to tell them in a song and sing it to them. He couldn't just speak the words about his loss. "

~ Becky in Long Beach