https://boxrec.com/en/event/488697
According to the note, a date for this event wasn't found. However, I found a preview for it in the Spokane Press on August 1, 1930. ("Two Good Men on Fight Card," Spokane Press, August 1, 1930: 5.) The date was scheduled for a miner's picnic in Kellogg, ID on August 15, 1930. This is confimed by an article on the 16th with the results (second round KO win for Firpo after a third KD in that round). "Firpo Winner On Knockout," Spokane Press, August 16, 1930: 5.