By 850 AD, the Chacoans began building large, multi-storied complexes called great houses. Pueblo Bonito is probably the best known of these great houses. It is the largest Southwest Native American building ever excavated, and at one time contained between 600 to 800 rooms. It was constructed in the form of a giant D, and was between three and four stories high. Construction in this canyon involved an amazing amount of organized manpower suggesting that there was an elite class. Chacoans harvested over 225,000 logs for the construction of the pueblos between 850 AD and 1250 AD. Many of these 500 pound logs came from as far as sixty miles away. Chacoans did not go very far for their rock and mortar. They quarried dark sandstone rock on the mesas above the canyon and held them together during construction by using a type of mud plaster. During the last stage of contruction the Chacoans plastered their interior and exterior walls until they were smooth. This protected the walls from erosion. Walls were painted in colors of either red, white, or a turquoise blue.