The spatial variables which affect the surface thermal regime are explored in a valley in a high-altitude catchment of the Andes of Santiago. Two one-year (2009–10 and 2010–11) ground surface temperature (GST) time series are analysed separately and linear mixed-effects models are used to quantify the effects of site characteristics on mean GST (MGST) and ground surface thermal regimes. The effect of snow cover onset and disappearance dates on MGST is further examined in a sensitivity analysis. Elevation has the strongest effect on MGST (1°C/100 m), 30 additional days of snow cover suppress MGST by an estimated 0.1 to 0.6°C and openwork boulder surfaces are cooler by an estimated 0.6 to 0.8°C. The sensitivity analysis corroborates the effect of late snow cover in the linear models, which can overwhelm the spatial differences in radiative effects. A positive MGST found on active rock glaciers would suggest negative thermal offsets probably related to the presence of coarse blocky material at the surface, and which may also be present outside rock glaciers. We suggest that spatial patterns of MGST can serve as a proxy for spatial patterns in the lower limit of permafrost occurrence. Copyright © 2012 John Wiley & Sons, Ltd.