The two-dimensional histogram technique is used to determine the loading dependence of friction on terrace and step sites of NaCl(001). An extended adhesion model is used to analyze the data. Both Hertz and JKR theory are incorporated for the elastic deformation. Depending on the model, sheaf strengths of 100-190 MPa are found at the terrace region. Increased shear strength values of 500-1800 MPa are found at the step edges that are interpreted in terms of the increased energy barriers at the steps, known as Schwoebel barriers.