Desperately Seeking Spike
Washington County is by far the largest county among the group. It is also part of a larger metro area. So set Washington aside just for a moment and think about the other 4 which are the core of Marcellus Shale development in Pennsylvania to date.. especially in the NE and north central parts of the state.
I just added up the employment counts for those 4 counties over the last 5 years and in aggregate this is what you get for the time series:
I must have made a mistake.