Making mounds out of molehills? The role of pocket gophers in the Mima mounds and vernal pools of the San Joaquin Valley (Part One)
By Dr. Sarah Reed, UC Berkeley. (Dr. Reed recently received her PhD, based in part on mima mounds studies she carried out in the Reserve and on nearby ranchlands)
Mound and trough are Siamese twins, joined by an invisible, crucial stratum that holds the ponded water. -- Hans Jenny
What are Mima mounds?
One of the most visually stunning, and scientifically puzzling, geologic features of North America are the small rounded hillocks called Mima mounds. Mima mounds are circular soil mounds found in grassland landscapes in nearly all states west of the Mississippi, as well as many places around the globe including South America and Africa.
Mima mounds are all found in regions with thin soil layers over a dense, impermeable substratum
Mounds occur only within geographic range of gophers
Occupancy (or evidence of past occupancy) by gophers of most Mima mounds
Uphill and moundward (towards the mound center) movement of soil by gophers (based on tracer studies of Cox and collaborators10)
Mounds have soils of a size small enough to be transported by gophers
Larger particle sizes at base and in between mounds.