IOWA, a north central state of the United States, situated between latitudes 40° 36′ and 43° 30′ N. and between longitudes 89° 5′ and 96° 31′ W. It is bounded N. by Minnesota, E. by the Mississippi river, which separates it from Wisconsin and Illinois, S. by Missouri, and W. by the Missouri and Big Sioux rivers, which separate it from Nebraska and South Dakota. Its total area is 56,147 sq. m., of which 561 sq. m. are water surface.

Physical Features.—Topographically, Iowa lies wholly in the Prairie Plains Region, part of it having been overrun by the Great Ice Sheet of the Glacial epoch. For the most part the surface is that of a prairie tableland, moderately rolling, and with a general but scarcely perceptible slope, which in the eastern two-thirds is from N.W. to S.E., and in the western third from N.E. to S.W. Elevations above the sea range from between 1200 to 1675 ft. in the N.W. to 500 ft. and less in the S.E., the highest point being in the vicinity of Spirit lake in Dickinson county, the lowest at Keokuk. In the southern half of the state the height of the crests of the divides is very uniform. The northern half is more broken and irregular; elevations, usually rounded, mingle with depressions some of which are occupied by small shallow lakes or ponds, the characteristic physical features of this region being due to glaciation. But the most marked departures from the prairie surface are in the N.E. and S.W. In the N.E. the whole of Allamakee and parts of Winneshick, Fayette, Clayton, Delaware, Dubuque and Jackson counties form the only driftless area of the state; in that section cliffs frequently rise almost vertically from the banks of a river to a height of from 300 to 400 ft., and from the summit of the cliff to the crest of the divide, a few miles distant, there is another ascent of 300 ft. or more terminating occasionally in knob-topped hills crowned in many instances with small cedar. Moreover, the largest streams have numerous tributaries, and nearly all alike flow circuitously between steep if not vertical cliffs or in deep craggy ravines overlooked by distant hills, among which the wagon road has wound its way with difficulty. In the W., S. from the mouth of the Big Sioux river, extends a line of mound-like bluffs usually free from rocks, but rising abruptly from the flood plain of the Missouri to a height varying from 100 to 300 ft. A broad water-parting extending from Spirit lake, on the northern border, nearly S. to within 60 m. of the southern border, and thence S.E. to Wayne county in the south central part of Iowa, divides the state into two drainage systems. That to the E., comprising about two-thirds of the whole area, is drained by tributaries of the Mississippi, of which the Des Moines, the Skunk, the Iowa with its tributary the Cedar, and the Wapsipinicon are the largest, streams of long courses and easy fall over beds frequently pebbly in the N. but muddy in the S., and through valleys broad at their sources, well drained, and gently sloping in the middle of their courses, but becoming narrower and deeper towards their mouths; that to the W. is drained by tributaries of the Missouri, mostly short streams taking their rise from numerous rivulets, flowing quite rapidly over muddy beds through much of their courses, and in the bluff belt along the Missouri having steep but grassy banks 200 ft. in height or more. (For geological details, see [United States], section Geology, ad fin.)

Flora and Fauna.—The predominant feature of the flora is the grasses of the prairie. The former forests of the state were of two general classes: on the bottom lands along the rivers grew cottonwood, willow, honey-locust, coffee trees, black ash, and elm; on the less heavily wooded uplands were oaks (white, red, yellow and bur), hickory (bitternut and pignut), white and green ash, butternut, ironwood and hackberry. The growth was heavier, however, in the E. than in the W., but, it has been estimated, covered in all about one-fifth of the area of the state at the time of its first settlement by the whites. In the N.E., also, small cedar and pine are found. But everywhere now most of the merchantable timber has been cut; in 1900 it was estimated that there were altogether about 7000, sq. m. of woodland in the state. The bison and elk long ago disappeared; black bear and deer were long found in unsettled parts of the state. Ducks, geese and other water birds are common, especially during their migrations.

Climate.—The climate is one of great extremes of heat and cold, with a dry winter and a usually wet summer, the prevailing wind of winter being N.W. while in summer it not infrequently blows from the S.W. Both the midwinter isotherm of Montreal and the mid-summer one of Washington, D.C., pass through the state. The mean annual temperature is 47.5° F.; the average range of extremes per year during the decade ending with 1900 was 136° F., while the greatest extremes recorded are from −43° F. in 1888 to 113° F. in 1901, a difference of 156° F. From 1893 to 1898 the average mean annual temperature at Cresco in Howard county, near the N.E. corner of the state, was 44.3° F., while at Keokuk in the S.E. corner it was 52.2° F., and as the isotherms cross the state, especially in the N., their tendency is to move S.W. The rainfall is also very unequal in distribution throughout the year, as also between the same periods of different years, and as between the different parts of the state. For while the mean annual precipitation is 31.42 in., 22.48 in., or 71% of this, fall during the six months from the 1st of April to the 1st of October, or 10% in winter, 23% in autumn, 28% in spring and 39% in summer, June and July being the two wettest months. At the same time extremes during the four most critical crop months, from the 1st of May to the 1st of September, have ranged from 6.75 in. in 1894 to 27.8 in. in 1902. Within any one year the precipitation is in general usually less in the western part of the state than in the eastern, the mean difference for all the years of record up to the close of 1903 being 2.5 in.; the western part also is marked by having a still larger per cent of its rain in spring and summer than has the eastern. The unequal distribution throughout the state is in much larger measure due to local showers. Injury to crops from drought and hot winds has occurred about two or three times in a decade, but liability to injury of the crops from excessive rainfall and hailstorms is greater than that from a deficiency of moisture. Three notable tornadoes have swept portions of the state: the Comanche in June 1860, the Grinnell in June 1882 and the Pomeroy in July 1893; but the greatest area traversed by any of these was less than one-twentieth of 1% of the total area of the state, and this kind of storm has been less destructive to human life, animals and buildings than the lightning which accompanies summer showers.

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Soil, Agriculture.—Its depth, together with its porous nature, makes the fertile soil of Iowa capable of withstanding the extremes of wet and dry remarkably well, and it is perhaps true that, taken as a whole, no other state in the Union has a superior soil for agriculture. Certainly no other has so many acres of improved land, or so large a proportion—from 85 to 90%—of its land subject to cultivation. The soil is of four kinds: till or drift, alluvial, loess or bluff and geest. The dark drift, composed chiefly of clay, sand, gravel, boulders and lime, is both the soil and subsoil of the greater part (about 66%) of the state, being especially predominant in the N. and N.W. The alluvial soil, composed of what has been washed from other soils, together with decayed vegetable matter, covers about 6% of the surface of the state and is found in the river bottoms, of greatest extent in that of the Missouri; it varies much in fertility. The loess soil, chiefly a mixture of porous clay and carbonate of lime, forms the bluffs bordering the bottom lands of the Missouri and is common in the N.E. Its fertility is not inferior to that of the better drift. Geest is found particularly in the north-eastern part of the state; it covers less than 1% of the area of the state.

The superior qualities of the soil, together with the usually warm and moist months of spring and summer, make Iowa one of the foremost states of the Union in agriculture and stock-raising, especially in the production of Indian corn, oats, hay and eggs, and in the raising of hogs, horses, dairy cows and poultry. In comparison with its other industries it stands also pre-eminently as an agricultural state; for of its 789,404 labourers in 1900, 371,604, or 47%, were engaged in agriculture, 129,006 being engaged in trade and transportation, and 124,803 in manufactures and mechanical pursuits. In 1899 the total value of the agricultural products, $365,411,528, was greater than that of any other state. Of the farms 65.1% were cultivated by owners in 1900, a decrease from 76.2% in 1880; and 19.5% were cultivated by cash tenants, an increase from 4.5% in 1880. After 1880 the percentage of farms operated by share tenants slowly but steadily decreased, falling from 19.4% in 1880 to 15.4% in 1900. Between 1880 and 1900 the average number of acres to a farm slightly increased—from 133.5 acres in 1880 to 151.2 acres in 1900—instead of decreasing as in the older states of the Union; though the increase was not nearly so marked as in such states as Nevada, Montana, Wyoming and Texas. Iowa about equals Illinois in the production of both Indian corn and oats, nearly 10,000,000 acres or about one-third of its improved area usually being planted with Indian corn, with a yield varying from 227,908,850 bushels in 1901 (according to state reports) to 373,275,000 (the largest in the United States, with a crop value second only to that of Illinois) in 1906. According to the Department of Agriculture in 1907 the acreage was 9,160,000 and the yield 270,220,000 bushels (considerably less than the Illinois crop); the yield of oats was 168,364,170 bushels (Twelfth U.S. Census) in 1899, 124,738,337 bushels (U.S. Department of Agriculture) in 1902, and in 1907 the acreage and crop (greater than those of any other state) were 4,500,000 acres and 108,900,000 bushels, valued at $41,382,000—a valuation second only to that of Illinois. In total acreage of cereals (16,920,095 in 1899) it ranked first (Twelfth Census of the United States), and in product of cereals was exceeded by Illinois only; in acreage of hay and forage (4,649,378 in 1899) as well as in the annual supply of milk (535,872,240 gallons in 1899) it was exceeded by New York only. In 1905, according to railway reports, 91,051,551 ℔ of butter were carried to points outside the state. It ranked far ahead of any other state in 1908 in the number of its hogs (8,413,000, being 15% of the whole number in the United States), Illinois, the second in rank, having only about half as many. It ranked first in 1900 in the number of horses (1,392,573); in the number of poultry (about 20,000,000); in the annual egg product (99,621,290 dozen in 1899); in the total acreage of all crops (22,170,000); in the total value of agricultural products; and in the total value of live stock ($271,844,034). In 1899 it ranked fourth in the production of barley (18,059,050 bushels) and in 1907 sixth (14,178,000 bushels). The wheat crop has varied from 12,531,304 bushels in 1903, 13,683,003 bushels in 1905, 7,653,000 bushels in 1907 (according to the U.S. Department of Agriculture), to 22,769,440 bushels (Twelfth Census) in 1899. Potatoes, apples and small fruits are grown successfully. For the most part the several crops are quite evenly distributed throughout the state; but nearly all the winter wheat is grown in the S. and N.W., spring wheat most largely in the N.W., barley mostly in the N., flax-seed and prairie hay in the N.E.

Minerals.—The first mines to be worked in Iowa were those for lead and zinc at Dubuque and to the northward. These are little mined at present, only 110 tons of lead ore and 516 tons of zinc ore being taken from the mines in 1908. Of more promise is the gypsum deposit extending over an area of about 50 sq. m. in the vicinity of Fort Dodge (Webster county), from which was taken in 1908 a product valued at $565,645, having increased to that figure from $45,819 in 1898. Limestones and sandstone are also profitably quarried, the value of the product in 1908 being $530,945 for limestone and $2337 for sandstone. The principal mineral of Iowa, however, is bituminous coal; it ranked in 1908 eighth among the coal-producing states of the Union, its product being valued at $11,706,402. The beds lie in the southern half of the state, extending under about two-fifths of its surface.