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To determine the effects of topography on soil genesis and development a physiography section of; Alluvial fans, Alluvial Colluvial fans, and Piedmont
- Alluvial fans in semiarid regions was studied in Kermanshah area. For this purpose . 8 profiles were selected from several digged profiles in toposequence , and classified according to Soil Taxonomy based on field studies and laboratory results . The results indicate that topography through influencing soil moisture relations , rates of replacment of materials in case of erosion and material transport in suspension and solution forms, was the main soil forming factor so that soil profile development had been resulted . This factor at cases of slope graduate and its lenght , has direct and indirect effects on Calcification, Melanization, and Gleyzation process, soil physical and chemical properties i.e. Color characteristics , clay percentage , calcium carbonate equivalent , S.P , pH, B.S , C.E.C and O.C. The type of identified horizons and main soil groups were affected by topographic position , and consequently Calcixerolls with Mollic and Cambic horizons, and Xerochrepts with Cambic and Calcic horizons in lower Situations had been formed Although , in all cases the type of clay minerals were similar, results of semiquantitatives analysis show that thier ralative occurence is different in the toposequence. In other word, due to drinage conditions and the effects of ground water with the increase in slope lenght, the amount of illite and cholorite had been decreased and the amount of semectite groupes have been increased.