O. J. Van Eck A.J. Feulner W. L. Steinhilber 1961 <p>Clayton County includes 784 square miles in northeastern Iowa and in 1960 had a population of 21, 962. &nbsp;For the most part, the county is a dissected upland that is drained mainly by the southeastward flowing Turkey River and its principal tributary, the Volga River. &nbsp;The Turkey River empties into the Mississippi River, which flows southward along the eastern border of the county. &nbsp;The climate is humid continental, and the average annual precipitation is 33.01 inches. &nbsp;The economy of the county is based on farming and the raising of livestock. &nbsp;The natural resources of the county include soil, water, rock, sand, and timber.</p> application/pdf en State of Iowa Geology and ground-water resources of Clayton County, Iowa reports