We know that Mint Of The United States At San Francisco Type I oval hallmark, large font, curved stem nine ingots like the one below, were the very first to have been produced and date to the early 1930's.
Recently I have found a few photos of the Old Mint that date back to this era. The one that follows is the neatest of the lot. From the information on the back of the photo, it is a night time shipment dated November 10, 1934
More photos to follow but had to get this one up first.