<p>Soil porosity is a key property controlling water movement, aeration, and soil structural functioning; however, its spatial behavior in stony soils at the small catchment scale remains poorly understood, despite its influence on infiltration, water storage, and hydrological processes in heterogeneous mountain landscapes. This study aimed to analyze the spatial dependence of surface soil porosity and its relationship with bulk density and rock fragment content in a tropical Andean catchment. The study was conducted in the Zanja Honda small catchment (Combeima River basin, Colombia). Soil sampling followed a stratified design based on Hydrological Response Units, with 46 sampling sites established across the catchment. Disturbed and undisturbed samples were collected to determine total soil porosity, bulk density, and gravimetric rock fragment content. Spatial autocorrelation was evaluated using Moran’s I, and spatial relationships were modeled using a Spatial Autoregressive Combined (SAC) model. Surface soil porosity exhibited significant spatial dependence and followed a log-normal distribution. The SAC model showed strong agreement between observed and predicted values (r = 0.91) and outperformed an ordinary least squares regression. Bulk density emerged as the dominant control on soil porosity, exerting strong negative direct and indirect spatial effects across the catchment. Rock fragment content also showed a significant but smaller negative influence. Surface soil porosity in heterogeneous mountain environments cannot be adequately described without accounting for spatial dependence. The spatial modeling framework improves soil physical characterization and supports the development of pedotransfer functions and hydrological models in Andean catchments.</p>