The only evidence of a three or four story structure may be rows of small holes in the cliff where the ends of roof beams once rested. A thin line of plaster running up the cliff may be the only indication of a high plastered structure that once stood there. Sometimes, fifteen or twenty feet up on a cave wall, a bright red spot may be seen on the sandstone. This is mute evidence that a structure once stood there for the red discoloration of the sandstone was caused by a small cooking fire that once burned on a third or fourth story roof. Thus the difficulty of estimating the number of ruins of any particular size is evident. In all probability, not half of the canyons have been explored to any extent by archeologists. Perhaps not more than one-third of the cliff dwellings, especially the small high ones, have been entered by anyone since the days of the early cowboys. A great deal of exploration and careful study will be necessary before the actual archeological wealth of the Mesa Verde will be known. [Illustration: Balcony House Balcony House, shown here, is an excellent example of the medium-sized cliff dwellings. In size it is near the top of the group for it contains two kivas and about forty-five rooms. In several respects Balcony House is one of the outstanding ruins and is the favorite with most visitors. Its location on the face of the cliff gave it outstanding defensive possibilities. The only entrance was a narrow ledge that ran about 400 feet along the face of the cliff. At one point the trail passed through a narrow crevice. This the Indians blocked with high walls and final access to the village was through a narrow crawl tunnel. The outstanding feature of this ruin is an excellent spring in the back of the cave. With this supply of water and their strong defenses, the people had little to fear from enemy raiders.] Below are four ruins that fall in the medium-sized group. They contain from twenty-five to forty rooms and are typical of the scores of ruins of this size that are to be found in the many canyons. In some of the ruins pictured few structures remain standing but careful search reveals evidence of the many rooms that have disappeared. These were once bustling little agricultural towns of a few dozen people. Without doubt the peaceful farmers prized the security of their high-flung villages. As more and more of the ruins are entered and studied, one fact becomes increasingly evident. Of the entire population of the Mesa Verde, relatively few people lived in the larger cliff dwellings. For every cliff dwelling of more than fifty rooms there were scores of smaller villages.