I'm assuming ze kvestion is something along the lines of "Does anyone here have any knowledge of/evidence for prehistoric earthworks in Washington?"

To which the answer is probably 'no' on both counts (though I'd love it if someone could prove me wrong).

I'd love to think there was still some traces of prehistoric activity in the area, it's such a lovely wide plain, early farmers in the region would have probably found it an irresistable spot.