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<:::> ..~ w ... c:; tI.;l 12 DEPLETION OF SURFACE WATER SUPPLIES IRRIGABLE AREA ON WESTERN SLOPE Before there can be any definite answer to the question as to how much land is irrigable on the western slope in Oolorado, there must be a clear definition of what constitues irrigable land. In Ohina and India, where every available acre of ground must be cultivated to pro- vide bare subsistence for the masses who would otherwise starve, any. land would be deemed irrigable to which water could physically be delivered. In other more favored countries olliy those lands on which a farmer could make a pr()fit would be deemed irrigable. Reasonable standards of desirability should be the measure of the extent to which irrigation agriculture may be expanded in Oolorado. Land classifications A very extensive survey was made about 15 years ago by the United States Bureau of Reclamation to determine the areas of land suitable . for irrigation in all of the Oolorado River Basin. This is generally , referred to as the Preston survey from the name of the engineer who .. was in charge of the work for several years. The irrigated areas were mapped but these were not classified as to soils or topography because the purpose of the Preston survey was to determine how much addi- ,tionalland might be included in new projects. Only two classifica- ,tions of arable and nonirrigated lands were used: Olass 1; Lands with ample depth of soil, good drainage, and topo- graphically suitable for the production of any crops. In other words, lands as well adapted to agriculture as any of the better lands now under irrigation. . Olass 2; Lands having shallower or less desirable soils, or somewhat deficient drainage, or slopes requiring special farming practices, or other limitations upon their usability. In other words, lands suitable tp some crops, but not to all characteristic of the region, and from which the farmer could derive less return for his labor than from class f land, , ,No attempt was then made to include lands which might be suitable for irrigated pasture or lands on steep slopes which might be used to a limited extent for orchards. These omissions have given rise to c<)nsiderable adverse criticism of the Preston survey,' particularly b~cause in recent years some parcels of land have been brought under irtigation which were not included in the irrigable areas mapped. . :More detailed land classification surveys have since been made by the United States Bureau of Reclamation which do not cover all of the western slope but do include the Oolorado River Basin above the coWluence of Gunnison River and a considerable part of the Gunnison River Basin. The land classifications used in these later surveys were similar to those used by Preston as to class 1 and class 2 but other lands suitable for irrigated pasture and orchards were included in the grd,up designated as class 4. Oontrary to expectations, the findings of the recent surveys confirm the soundness of the work done by Preston within the areas mapped by him. For example: (a) The more recent and detailed classification surveys of all lands along the main stem of Oolorado River and its tributaries above Gunnison River show a total of about 121,000 acres of class 1 and clas$ 2 land, but the potential projects known as the Oliffs-Divide projects and the Silt and Oollbran projects only include 79,400 acres ?:: '{." ,i~ .;. ~ . t> .-