Prehistoric Puebloans built dozens of village sites across the Caja del Rio and Pajarito plateaus. In contrast to its western neighbor, however, the canyon walls of the Caja are frequently made of basalt, rather than welded tuff. The latter material is much easier to excavate, and as a result, the Pajarito contains many more cliff houses. Both areas, however, contain countless petroglyphs. Most of them have been pecked into the ubiquitous basalt.