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Measuring over 453 faults with slickenside lineation on 28 Karaj Formation localities in southern part of central Alborz, different methods including: conjugate faults analysis, R% method , fluctuation histogram of and right dihedra model were tested comparatively .On the basis of these methods, the arithmetic mean of the angle of internal friction determined to be 35.75 degrees in the whole study area. In different localities low internal angle coincides with high fracture density, low topographic relief and vice versa. Interception of misfit-angle curve with ordinate axis shows astonishingly the same magnitude as the mean angle of rock-mass internal friction.