This study uses ethnographic field data to derive an asymmetrical Cauchy (Gaussian) equation that describes the movement of a llama caravan along an ancient trail system as a function of topographic slope. This model is further refined by using ranked observations of changes in trail quality, the negotiation of obstacles such as stream-crossings, and the type and duration of rest periods during the daily travel. The resulting cost-distance function was then applied to the actual caravan route in order to evaluate the realism of the model.