Marshall county is located in central Iowa, almost in the exact center of the state. It lies partly in the Iowan drift soil area and partly in the Southern Iowa loess soil area. Hence, both drift and loess soils are found in the county, the area covered by loess being very much larger, however, than that occupied by the drift soils.
Stevenson, W. H. and Brown, P. E., "Soil Survey of Iowa, Report No. 25—Marshall County Soils" (1922). Soil Survey Reports. 27.