Lost mines and buried treasures of old Wyoming by Jameson has two in NE part of the state. Pages 63 and 77. The later one was the one with gold bar in bank window in Iowa.
I couldn't find any articles on this one Using a KeyWord Search .
And if Jeff can't find it and my wife cant find it, then I consider the possibility that creative writing around historical truth could be involved. We hit a few stories up in Montana the same way. That's why some folks claim the lesser known could pay off better.