and here is one more comprehensive recent reference 

http://www.bbc.com/earth/story/20141028-the-strange-origins-of-mima-mounds

as far as Native Americans go

1.  When originally discovered in 1840 something, the discovers thought they were native american burial grounds, so naturally, like exploiters, they dug them up but found no bones, just rocks.

2.  The local Native population does not have the creation of the mimi mounds in their campfire stories.  That is significant.

Hello, recently Gabet et al (2014) conclued on the non human origin. For the author they are build by gophers.

Emmanuel J. Gabet, J. Taylor Perron, Donald L. Johnson, Biotic origin for Mima mounds supported by numerical modeling, Geomorphology, Volume 206, 1 February 2014, Pages 58-66,.

There are similar geomorphic features in Oklahoma (although lower in elevation), usually referred to as "pimple mounds", that also are inferred to be natural and not cultural. Such features have a high probability of being large-scale soil structures (kinds of "macro-peds") that we do not yet understand in terms of formation and causes. Although not analogous in terms of their morphology, such  soil features as desert pavements (in the Mojave Desert (see Wells & McFadden) form through an input of eolian sediments in ways not anticipated prior to a concerted investigation. The regularity and extent of at least some of these mound features strongly suggests pedogenic processes at a not-unexpected scale of formation that has simply been outside of our perspectives on soil formation. 

Thanks for your replies.  If the Mima mounds in the West are determined to be old farm fields, then they are the largest archaeological remains that still exist, because all other evidence (other than some cave painting, grinding rocks, desert effigies and rock art) that California Indians lived here for many thousands of years, has been wiped off the face of the planet after the European occupation.  

If we look in the Eastern United States, there was a huge Mound-building culture around the Great Lakes, Ohio and Mississippi rivers.  Why not a smaller agricultural Mima mounds building culture here in the West?

I have been to Cahokia mound across the river from Saint Louis, so a field of Mima mounds constructed to grow their edible bulb crops seems very reasonable.

I love the view, that we would rather attribute these mounds for decades to gigantic gophers, rather than Native Americans?  Why is it so tough for us  to include the Native Americans as one of the possibilities?

 From a agricultural perspective, the mound position within a wetland, and their round shape, height and size, and finding the relict crops of native bulbs still growing in them, should provide archaeological evidence that they were farm field, and should be investigated?

Many of us here in the PNW believe these features are associated with melt water/sediment features at the end of the last ice age (about 7500 years ago)

http://www.rainiervisitorguide.com/mima-mounds.html

is a decent reference

Yes, meltwater, gophers, ground heaving, windblown sediment, earthquakes--but why have the European occupants of North America always considered everything except for Native Americans?  Anyone ever ask the Native Americans if their ancestors made them?

When you view the Mima mounds around Weed, California and see the edible bulbs still growing in them, it just looks too much like a constructed agricultural field, and the height is just right to keep the bulbs moist year round but not too wet, and the round shape and diameter, would be just the right size for a few people to be sitting on top, managing the crop.

 If we looked at the plant phytoliths, both right within the mound, then the plant phytoliths in the wetland areas adjacent to the mound, we may find that it was a planted crop of top of a constructed high point by the Native Americans.  Then, these mounds would need protections as significant archaeological sites, instead of only being protected currently as geological or giant gopher curiousities.

If anyone gets a grant to study these mounds as potential American Indian edible bulb  fields, I would like to be included as a co-author on that paper. 

and here is one more comprehensive recent reference 

http://www.bbc.com/earth/story/20141028-the-strange-origins-of-mima-mounds

as far as Native Americans go

1.  When originally discovered in 1840 something, the discovers thought they were native american burial grounds, so naturally, like exploiters, they dug them up but found no bones, just rocks.

2.  The local Native population does not have the creation of the mimi mounds in their campfire stories.  That is significant.

I believe once the mounds was constructed by the Native Americas, then gophers could come and occupy them, especially after the Native Americans who were managing them were exterminated by the Europeans.  

However, the Mima mounds around Weed, CA. could not have been started by gophers, because that is a perennial wetland area, and the gophers would have not been able to burrow into that wetland to build up the mound in the first place.  

There is a clue that they were farm fields, in that BBC article you have linked, in that the Mima mound itself has richer soil than its surroundings. 

Craig,

I have seen many Mima mounds on the Awapa Plateau (aka Parker Mountain) in Wayne County, south-central, Utah. These mounds may have likely been developed by Utah prairie dogs, pygmy rabbits, or ground squirrels excavating soils with more friable textures.  These mounds are inhabited by big sagebrush and as you indicate above also include more productive herbaceous vegetation underlying the big sagebrush.  At some points the mounds appear to be uniformly spaced, which may have something to do with spacing behavior of Utah prairie dogs.  Excavating and then enriching sites with urine and feces would create these fertile shrub islands in an otherwise arid landscape. Hard for me to envision Native Americans uniformly spacing bulb farms across such a large landscape.  Perhaps the Native Americans capitalized on digging up bulbs growing on the mounds, but the mounds were created by fossorial mammals?.

Cheers,

Jeff

Not sure. It is very likely that Native Americans collected observations which site conditions are most favorable for bulbs. As far as I know, especially Camassia was a staple food in some regions. Moreover, having knowledge on the optimal conditions, it is not unlikely that they tried to improve the sites. However, investing work into a "crop" is becoming uninteresting, if maybe somebody else might harvest it. So, I expect that some archaeological findings should be associated with these mounds, e.g. some remains of villages of Native Americans (or at least some broken tools or lost artefacts). However, if created by Native Americans, it need not be the people that were present at time of contact. Maybe, in the period before Athabaskan tribes immigrated from North, the times (and tribal territories) would have been more stable and more favorable for some kind of agriculture? Anyway, if it cannot be supported by some findings, this is speculation.

Craig, thanks for the discussion.  I recently finished a study on the mounds, focusing on the gopher hypothesis.  I'll add a few thoughts.  

Perhaps the idea of humans as builders of the mounds has been under-studied.  As others have mentioned, that idea hasn't been pursued much due to the facts that no human artifacts have been found in any excavated mounds.  I only found a few references to Native Americans and Mima mounds in my research, mostly about Native American stories of origin.  

For instance, the mound creation story of the Miwok Indians of the Central Valley, California goes something like: " The Miwoks were under constant attack by marauding Nevada tribes. Miwok women took up their burden baskets, filled them with earth and then piled them on top of each other to form an earthen wall, too high and too strong for the eastern tribes to surmount. Thus the Sierra Nevada mountain range was formed. When the work was done, and their enemies were repelled, the exhausted squaws dropped their empty baskets wherever they stood and walked away. Those baskets, according to legend, are the mima mounds."    (From http://www.newsreview.com/sacramento/pool-on-the-hill/content?oid=5468)  

Also, attached is a picture showing the Yokuts tribes built their houses among Mima mounds.  (I think this is from the book The Great Central Valley: California's Heartland).  

For more reading, a recent Geological Society of America book includes a very thorough lit review and analysis of Mima mound research.  (Full disclosure:  I am an author of one of the book chapters). http://specialpapers.gsapubs.org/content/490.toc

While I think mounds in different locations could certainly have different origins, I'm pretty convinced of the role of gophers, especially in California's Central Valley.  For my thesis,  I did a spatial analysis (using LIDAR data) of nearly one-quarter million mounds to study their pattern across a landscape (a 3 million-year-old chronosequence).  I found increasing mound height and regularity (mound dispersion) with soil age and with the development of restrictive soil layers (like hardpans).   In addition, the widespread regularity in mound distribution closely matches the strict habitat spacing of territorial gophers.  While many of the previous Mima mound studies have yielded results which are consistent with multiple explanations, I believe the clear pattern of mound change with pedogenesis is only predicted by the gopher hypothesis.  

The idea is that as soils age and/or soil effective soil depth (friable soil above hardpan) decreases, environmental pressure on organisms inhabiting the soil increases, prompting a response via increasingly directional (and thus constructional) sediment transport. This should lead to an increase in mound height and density if gophers are responding to decreasing habitability, which was the pattern observed.  

There's more here if you're interested:  

http://search.proquest.com/dissertations/docview/1528536573/abstract/F5CC57EF89CF4A65PQ/1?accountid=14496#

I've always been interested in the role Native Americans may have played in either the origin or subsequent evolution of the mounds.  If you come across any useful references, please pass them along!  

Finally, a few more plant-related references you might find interesting. 

Storm, Linda, and Daniela Shebitz. "Evaluating the Purpose, Extent, and Ecological Restoration Applications of Indigenous Burning Practices in Southwestern." Ecological Restoration 24.4 (2006): 257.

Klein, Janet L. Vegetation patterning relative to Mima-like mounds and its implications for a tallgrass prairie restoration in southerwestern Missouri. University of Wisconsin--Madison, 1998.

Brotherson, Jack D. "Vegetation of the mima mounds of Kalsow Prairie, Iowa." Western North American Naturalist 42.2 (1982): 246-261.