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r-- y~ ":'"~"l 01 (~.:.-~ C fan having less than a one percent gradient. Only scattered small tracts and some broad areas of bottom land have an uneven surface rendering irri- gation practices more difficult or requiring considerable leveling and SOme grading. Extensive areas of bottom land bordering the streams and several hummocky, gravelly-soil tracts on the outwash plains have a topographic character which precludes their economical development. The system of sUbirrigation, somewhat exclusively practiced in other parts of the San Luis Valley, is demanding of an exacting micro-relief and nearly smooth land surface in order that the level of ground waters can be maintained at a uniform, shallow depth to achieve maximum crop production, The prcvision of an adequate water supply for the Conejos Division would favor an increase in th8 present extent to which subirrigation is employed, and considerable land leveling would, therefore, be undertaken to attain the finer degree of gradient and surface requisite for this practice. ".-, , Drainage The higher-lying, coarse-textured soils of the outwash plains exhibit good to excessive drainage characteristics, altheugh there are numerous scattered depressions and swales where some seepage and accumulation of water occurs. The principal preblem of inadequate drainage extends through_ out the bottom lands and in a region of floWing wells north of Manassa and Sanford where ground water from the higher lands accumulates, bringing the water table close to the surface. The necessity for flood control is apparent where seasonal floods inundate the lowcst tracts along the river and contribute to high water table conditions, but substr~tial lowering of the high ground-water table will not be effected by the control of floods alone. Salinity and Alkalinity The majority of soils are relatively free cf excessive concentrations of ~oluble salts and are not highly alkaline. Coincident with seepage and drainage problems, the lower-lying lands, particularly those situated north of Sanford, are affected by mCderate to high accumulations of salines, the soluble salt content in many cases exceeding one percent. Many of, them are open, porous and r.ot strongly alkaline, and the possibility of their reclamation by leaChing, drainage and other measures appears favorable. Several areas of structure less, solonetzic soils cannot be Successfully reclaimed. Land Classification A detailed classification of the lands in the Conejos Division was completed to determine the extent and character of the lands and their suitability for irrigation agriculture (See Conejos Division'General Land Classific~tion,Map). The survey involved the determination and delineation of the lands into six classes acc~rding to productive capacity, establishad in respect to and by consideration of factors of SOils, topography and draina<ge. The classification standards used in the survey to accomplish thi~ ,segregation are defined as follows: 1'7 ,