Indian dwellings in the canyon at Walnut Creek. Photo by: Jan   Date: _ Outside Flagstaff in Arizona is Walnut Creek Canyon. It has a number of limestone overhangs that the indian inhabitants used to build homes. They walled up the front of the overhang and installed an ingenious venting system so the cooking fire smoke would exit whilst the fresh air came in and circulated at the same time. Click on image for next in series or here for the index