On my way today to the Washington spring trappers get together I passed through the "mima mound" region in southwest Washington. It amazes me that even with our understanding of so many deep scientific subjects, we still don't know how these were created.

I don't buy into either the "wind blown sediments" theory, or the "gopher mound theory". I've looked at these mounds before, they are mostly coarse, alluvial gravels, with cobbles too big to be heaved up by gophers, or blown by wind.

They say these exist elsewhere; any where you live?

Not that mound but pocket gopher yes.

Could it be from some prehistoric upwelling of water carrying the gravel?

Lava flow!

Injin mounds

I was always told growing up those were glacier created in the ice ages. Didnt know there was even a controversy on how they were created.

^^^^^^
My thoughts were some sort of frost/freezing action. These particular ones are in a glacial outwash plain at the extreme south end of the Puget lobe of the last continental glacial episode which came to an end 12-15 thousand years ago. I sort of doubt that this area has ever had a history of permafrost though.

Looks like the Grand Mound/Rochester area, in Thurston county.

Yep.

The only problem with the freeze/thaw theory imo, is this gravely soil is very well drained. Maybe water was impounded at some point in time though.