Mixed monolayers of C-70 and octanethiol are prepared on Au(111) by a sequential adsorption method. A partial C-70 monolayer is first formed and characterized, followed by the vapor deposition of octanethiol. This results in a well-ordered alkanethiol film where single C-70 molecules and small molecular clusters are located at domain boundaries and in disordered regions. Substrate step defects have a large influence on the spatial distribution of C-70; adjacent to a substrate defect, C-70 binds preferentially on the upper terrace and is depleted on the lower terrace. We explain these observations as resulting from the kinetics of alkanethiol monolayer formation, and we present a simple model for the evolution of surface structure in the C-70/octanethiol system.