In a hydrographic watershed, the erosionability (K factor) of the soil evaluation depends on the technical resources, developed applied sciences, and spatial technology available. For the determination of erosionability in the watershed of Pillahuinco Grande`s Creek (Argentina) (38°S, 61°15´W), the Universal Soil Loss Equation (USLE) was used by applying a geographic information system (GIS) for the cartographic evaluation. A database of geological, environmental, and soil associations was developed, which indicated that geomorphologic variability, caused by geology and soil, signifi cantly determines the spatial variation of the K factor values, in a range from 0.02 to 0.69 ((t·m2·h)·(ha·J·cm)-1). A new quantifi cation was determined with the simplifi ed K factor from the USLE model and with the two generated equations, K1, starting from sand, silt and organic matter, and K2, beginning from sand and organic matter. A linear regression and the coeffi cient of effi ciency (RN 2) were established, which indicated the adjustment of the K factor for each developed pattern. The RN 2 correlation value was 0.76 in relation to the simplifi ed K factor, 0.87 to K1, and 0.86 to K2 (very similar due to the small signifi cance of silt in the equation). This relationship demonstrates that the application of K1 and K2, according to the readiness of the data, is more specifi c and exact than the results obtained by applying the simplifi ed K factor.