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, significantly 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 quantification was determined with the simplified 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 coefficient of efficiency (R N²) were established, which indicated the adjustment of the K factor for each developed pattern. The R N² correlation value was 0.76 in relation to the simplified K factor, 0.87 to K1 , and 0.86 to K2 (very similar due to the small significance of silt in the equation). This relationship demonstrates that the application of K1 and K2, according to the readiness of the data, is more specific and exact than the results obtained by applying the simplified K factor.