My little hometown has a mine-resistant vehicle. Those things are expensive to maintain. Now I know why the libraries and parks in such disrepair!

Why does Sweetwater County, Wyoming, population 45k, need 60 assault rifles? Why does any rural police force need any assault rifles?

I would say a likely reason is because of budgets: They were given the money if they didn't spend it, they would lose it. Might as well buy guns that can be traded for something else in the law enforcement system than let the money "go to waste".

Another idea could be that they have Rt.80 and have lots of transportation related crime?