The area described in this report is in southwestern Minnesota, about 130 miles southwest of Minneapolis and St. Paul. It includes Nobles County and the western tier of townships in Jackson County, a total of 864 square miles. Worthington, the Nobles County seat, is the largest city in the area, having a population of 9,015 persons (1960 census). Farming is the leading occupation, and food processing is the major industry. Critical water shortages have occurred in several parts of the area.
The, climate is characterized by mild, subhumid summers and relatively long, severe winters. Mean monthly temperatures range from 15.1?F in January to 73.3?F in July. The mean annual precipitation is 26.75 inches. The crest of the Coteau des Prairies, a broad highland belt, Traverses Nobles County from northwest to southeast. Three glacial end moraires and their associated ground moraines trend south to. southeast across the area. Altitudes range from about 1,820 feet on the crest of the coteau in the northwestern part of 'the area to about 1,390 feet above mean sea leve1 in the Jack and Okabena Creek valleys in the northeast.
The Mississippi-Missouri River drainage divide crosses the are from north to east. The Cary outer end moraine trends southeast through central Nobles County. East of this moraine the land is poorly drained and contains numerous lakes and swamps; west of this moraine the land is well drained and contains few, if any, undrained depressions.
Within the area, granite and Sioux Quartzite of Precambrian age are overlain by cretaceous strata, except locally in the northeast and northwest parts of the. area where the quartzite, is directly overlain by glacial drift. The Cretaceous strata are composed of interbedded shale, siltstone, and sandstone. The surface of the area is composed of. Pleistocene deposits of glacial drift and some thin, patchy deposits of Recent age. Bedrock is not known to crop out in the area. The drift ranges in thickness from about 150 feet in the southwest and .northeast corners to about 500 feet on the highest part of the Coteau des Prairies.
The Precambrian granite is not a source of ground water in this area. The Sioux Quartzite yields moderate supplies in adjacent counties to the north and west, but because of its sporadic occurrence it does not constitute an important-water source in this area. The- Cretaceous sandstone, units are a secondary source of ground water and yield adequate supplies to at least 24 farm wells, which range in depth from 283 to 586 feet below land surface. The primary source of ground water in the Nobles-Jackson County area is
the glacial drift. Buried outwash deposits supply water to 7 of the 10 municipalities and to most of the farms in the area. Two Worthington city wells, completed in a buried outwash deposit underlying East Oklahoma dry lake bed, were tested for short periods at 500 gallons per minute. The estimated coefficient of transmissibility for the aquifer and one of the wells was 70,000 gpd (gallons per day) per ft.
The buried outwash deposits may occur anywhere within the drift from about 15 feet below land surface to bedrock which is as much as 500 feet below .rand surface. The outwash ranges from a fraction of a foot to more than 25 feet in thickness where permeable; below the water table it generally will supply ample quantities of water to properly constructed wells.
Surficial outwash deposits fill the valley bottoms and form the terrace deposits associated with the present-day drainage channels. The thicker, more extensive, and continuous deposits occur in the preglacial stream channels that drained the fronts of the ice sheets rather than in those channels that now drain the backs of the moraines. The surficial outwash deposits generally are made up of sand, gravel and some silt and clay, and range in thickness from 0 to more than 60 feet; they range in width from a few feet in the narrow tributaries to about one mile in the lar
Additional publication details
USGS Numbered Series
Geology and ground-water resources of Nobles County, and part of Jackson County, Minnesota