Soil Survey of Iowa, Report No. 29—Mahaska County Soils
Mahaska county is located in southern central Iowa in the third tier of counties north of the Missouri state line and in the fourth tier west of the Mississippi river, as shown in the accompanying map. It lies entirely within the Southern Iowa loess soil area and hence the soils of the county are mainly of loessial origin. There is only one type derived from glacial material and that has been formed by the washing away of so much of the surface covering of loess that the drift material makes up most of the three-foot soil section.