Some Copán houses found near hillsides show debris from erosion. The probable cause of this erosion is that people were overfarming the hillsides. The erosion seems to have begun in the mid-eighth century (based on evidence from obsidian dates) and to have continued for a long time afterward. At some point, these houses were abandoned. Eventually, some houses were completely buried by erosion debris.

The Maya used obsidian, a glass-like mineral, to make cutting blades. Obsidian blades were widely used in households in Copán, and many blades have been found. The dates of these blades reveal how populated the valley was. Obsidian blades found in Copán households show a range of dates, from A.D. 500 to 1200. After A.D. 950-1000, the number of blades drops off.