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Fort Pueblo. These posts did a thriving business, encouraged settlement. and flourished until the decline in fur trade. Then, they were abandoned and subsequently replaced by military forts for the protection of the settlers. The latter part of the 19th Century could be classified as the mining era. which began with the discovery of gold in 1860 near Leadville. A variety of mine~als was produced, and this industry stimulated the growth of others such as railroad transportation, lumbering. and the manufacture of mining machinery and equipment. These developments attracted thousands of people to the area. thus providing an increasing market for agricultural products (4). 3.2.2 20th Century with the beginning of the 20th Century, agriculture and related food processing industries became the dominant factor of economic development until World War II. Cattle ranches spread over the plains and immigrants from the Midwest took up homesteads and laid out farms in the valleys where they could install minimum facilities for irrigation of crops. As the demand for agricultural products grew, farms were enlarged and irrigation enterprises were organized. These industries established a more permanent type of settlement, and the population grew rapidly (4). 3.3 Significant Impacts of Economic History on River Morphology The economic development of the Arkansas River valley significant impact on the morphology of the river. Settlers, farmers and ranchers, altered the natural conditions with crops and, as the population grew, impacts on the river increased. has had a particularly and livestock Irrigated agricultural practices eventually changed the natural hydrologic character of the river. By 1895 there were 20 major irrigation diversions between Pueblo and Kansas (2). These diversions also removed large volumes of sediment with the irrigation water. The effect of crop irrigation was to raise the water table (via recharge) above the river bed in late summer and to change streamflow from intermittent to perennial. The perennial river could support other types and amounts of riparian and floodplain vegetation. Areas of prairie decreased as shrubs and trees took hold. The exotic species salt-cedar (Tamarix ramosissima), a phreatophyte native to the Mediterranean, was first observed in the Arkansas Valley in 1913 and today thrives along the river. This increase in vegetation reflects an increase in soil moisture due to the higher water table, a result of increased irrigation. These hydrologic and vegetative changes produced major morphological changes along the river. Nadler (2) states that the river narrowed considerably between 1926 and 1952 (215 m to 46 m); the 1952 width was only 2l~ of the 1892 width. The sinuosity of every reach of the river was greater in 1977 (1.43) than it was in 1870 (1.15). 7