This paper investigates the spatial variability characteristics of geologic profiles, including variations in thickness of marine clay deposits and rockhead levels, based on borehole data obtained from four sites in Hong Kong. The numbers of boreholes are approximately 100 in two cases, while the other two cases comprise more than 300 boreholes each. The large volume of data allows comprehensive statistical analyses to identify the spatial correlation/variability in subsurface profiles using the Restricted Maximum Likelihood (REML) method. The Matérn Autocorrelation model is adopted for its flexible functional form, with the parameters optimized using the Differential Evolution algorithm, in order to maximize the log likelihood value in REML. This technique is used to evaluate the spatial variability characteristics of geologic profiles, including parameters such as the spatial dependence and scale of fluctuation at the four sites. The effects of irregular sampling pattern, sample domain scale and sampling density on these parameters are also discussed based on the analyses. In addition, the existence of faults in two of the sites is found to significantly affect the spatial variability of rockhead level, as indicated by the reduced scales of fluctuation and spatial dependence in areas intersected by faults.