The relative size of contemporaneous rock glaciers is controlled by the intensity of the rockfall processes and the preservation of an ice matrix/core which induces flow. Topoclimatic parameters (altitude, radiation reduction by topographic shading, and position of the cirque or wall with respect to wind-drifting/avalanching of snow) determine the potential for preservation of this ice matrix. Jointing of the bedrock source walls appears to control, at least in part, the production of debris by rockfall. The correlation structure of these variables suggests that topoclimatic and jointing variables interact, rather than exert additive effects to influence the relative development and location of rock glaciers, and that the scale of analysis has a direct effect on the significance of variables. A multiple regression model incorporating the main effect of radiation shading and an interaction term representing the product of altitude, radiation shading and jointing of the source walls explained 72% of the variance in the size of the rock glaciers in the study area of the Sangre de Cristo Mountains, southern Colorado. The analysis further suggests that Evans's law of decreasing asymmetry with increasing coverage can be extended to include periglacial as well as glacial lithofacies deposition.