Two measured and weighed assemblages of lithic debitage were subjected to human treadage, one set on a compact sandy silt (“loam”) substrate, the other on unconsolidated sand. The assemblages were excavated, plotted in three dimensions, and documented for damage. Downward migration of pieces at the loam site was minimal: fracture of small pieces was the dominant damage pattern. Most sand site pieces migrated to 3-8 cm depth; vertical distribution of pieces approximated a normal curve, and edge-damage to larger pieces was the dominant damage pattern. Vertical distribution of artifacts at the sand site approximated a pattern observed in two other trampling experiments and a number of archaeological occurrences. Factors influencing these distributions are discussed.