Riparian areas are important ecosystems in range-lands. Surface runo and soil loss from the un-grazed and grazed areas of sheep Creek Colorado, U.S.A. were simulated using the Areal Non-Point source Watershed Environment response Simulation (ANSWERS) model. The ANSWERS model parameters were estimated from eld measurements and published literature. The mean runo, soil loss, maximum erosion and maximum deposition rates simulated by the ANSWERS model were significantly higher (P = 0.05) for the grazed areas then for the un-grazed areas. Evidence indicated that livestock grazing in the sheep Creek riparian zone reduced inltration, which, in turn, increased runo and soil loss but of minimal biological importance.