Fortunately it's an old story, easily explained, easily managed. From Montana State University almost one year ago at msuextension:
Due to Montana’s arid environment, we tend to have soils with a high pH, usually ranging from 6.5 to 8.5.
The average soil pH for Broadwater County is about 8.0.
If you have a high pH soil, one of the first questions you’ll likely ask is “how do I change it?” Unfortunately, it’s not easy.
The two most common amendments to lower pH are sulfur and aluminum sulfate. Aluminum sulfate works more quickly, whereas sulfur can take several months. Routinely adding organic matter can also improve the pH. Always be cautious when adding fertilizer and soil amendments. Too much of a good thing, isn’t always a good thing. Use your soil test to determine how much fertilizer or organic matter should be used.
Acidic soils and the need to raise pH is rare in Montana. Cropland in central Montana are starting to have an issue with soil acidification due to high inputs for many years, but this is rare. Limestone is the common amendment used to raise pH.Broadwater County, Montana, is pretty much near the center of the state, just east of Helena, and a long, long way from the Bakken.