The gopher camp for Mima Mound formation has another paper out Biotic origin of Mima Mounds supported by numerical modeling.
Mima Mounds are named for Washington States Mima Praire south of Olympia. However, Mima Mounds are found in many other areas including extensive areas in eastern Washington. They have been driving geologists crazy for 100 years or more.
Gophers have been suggested for the formation of the mounds. Not a single gopher wanting to build a large mound, but multiple generations of gophers moving soil in a preferential manner as described in the paper linked above. The idea has been around for some time and for many mound sites it makes sense and actually seems very likely. However, the Mima Mound Prairie itself as well as other nearby prairies in southwest Washington with and without mounds presents some still unresolved challenges to the gopher camp.
There are still other competing theories for the southwest Washington prairies and some relatively new information on the the geology of the underlying gravel units (Goldstein, Pringle and Futornick, 2002).
(Washburn, 1988) provides an excellent overview of the Mima Prairie and other nearby prairies and has a matrix of the various proposals for mound formation which leans to a sediment anchoring model. Given the newer data and particularly the LiDAR imagery of the southwest Washington prairies a revised matrix after Washburn might be an interesting exercise.