The northwestern mound, used for formal burial, was also built in three stages. A special structure, approximately by , with its long axis towards the northeast/southwest, was built on the west side of the mound. Its doorway was in its southwest corner, and the structure was covered with a mixture of clay, willow branches, and grass. The floor was covered with a mat of what may have been cattails. The bodies of ten people were placed side by side on this, with their heads toward the doorway. The bones of another person were bundled together with cord and placed near them. Once this construction was complete, and the bodies were inside, the building was burned.