An evaluation of the spatial correlation length of two geological formations known as mudflows and residual soils has been conducted using standard penetration test (N1)60 values. The spatial correlation length is an important property in reliability-based design, in addition to the mean and standard deviation of soil parameters, but it is rarely estimated in geotechnical projects. Reported results in this paper from both geologies show the geological origin's importance in the spatial variability analysis. Residual soils are more likely to display isotropic spatial correlation lengths horizontally when compared with the mudflows. The results show that the random field represents more accurately the mudflows' soil variability when the residual soils must be complemented with shear strength tendency analyses.