Geology and ground-water resources of Webster County, Iowa

Webster County, comprising an area of 718 square miles just northwest of the center of Iowa, had a population of 44,241 in 1950, with 25,115 in Fort Dodge, the principal city. Some 94.4 percent of the county is in farm land; corn is the principal crop and is used in the raising of hogs and cattle, an important oc cupation in this part of the country. Mineral products include gypsum, clay, coal, sand, gravel and limestone.

The mean annual precipitation at Fort Dodge is 31.21 inches, of which more than 3 inches normally occurs during each of the months May, June, July, August, and September. The average number of growing days is 150. The warmest month generally is July; during December, January, and February the average temperature normally is below freezing.

The upland area, comprising over 80 percent of the county, is mostly a gently undulating, slightly eroded glacial-drift plain. Morainal hills of low relief occur in the extreme southern and northern parts of the county. The Des Moines River flows through the county from north to south and, together with its tributaries, drains the entire county except the southwestern part, which is tributary to the Raccoon River. The Des Moines River has cut a deep, narrow valley about 90 feet below the upland in the northern part of the county and about 220 feet below the upland in the southern part. The tributary streams commonly have shallow valleys more than a few miles back from the Des Moines River.

Glacial deposits of Pleistocene age, ranging in thickness from 50 feet in the north to 175 feet in the south, mantle the indurated rocks over all the upland area, but indurated rocks ranging in age from Mississippian to Cretaceous are exposed in places along the valleys of the Des Moines River and its tributaries.