I sounded out John Dye, owner of Bryant’s Cocktail Lounge and At Random in Milwaukee, and he said this:
“We don’t have any variations of a stone sour on our menu. We usually come across that term when someone uses it as a modifier on a Wisconsin style old fashioned (e.g., Brandy Old Fashioned Stone Sour). I’ve seen variations where it is half sour soda (Squirt or 50/50) and half orange juice or lemon based sour and orange juice. When I worked a bar in the early 2000s we made a ton of Amaretto stone sours. I had never heard that term on the west coast.”
John is originally from Montana, fyi. So you idea that it’s a Midwestern thing.
Did a quick search and that Amaretto Stone Sour seems to have been crazy popular in the Midwest in the 1990s and 2000s. The recipes seems to check out with what Dye described.