Chances are good that these are cluster hops. Around 100 years ago (don't know exactly when) salesmen came up from Chicago to sell various plants through Wisconsin and the upper peninsula of Michigan. One of the things sold were cluster hops, so if you find a bunch of these things growing wild, they likely are clusters that escaped from an old homestead. Kind of like why there are so many Lombardy poplars in the area.
Alpha acids are highly variable depending on weather, and how the plants themselves have adapted over time, but if you look at the typical range for clusters and pick something in the middle, it's a good starting point.