When the lake was at its maximum size the water reached a height where it began to flow over the top of the lava dam. During thousands of years of spilling over, the water gradually wore down through the lava until the entire lake drained away. The limestone that had been carried in and deposited on the lake bottom then became the new ground surface. Salts left by the evaporation of water were also deposited on the lake bottom. A deposit of this type can now be seen near Camp Verde. Although the formation is principally sodium carbonate, sodium chloride (common table salt) and sodium sulphate are also found. For many centuries early Indians mined salt deposits in this locality and a few years ago a deposit of sodium sulphate near Camp Verde was worked commercially. The same streams which brought lime in solution to the lake were sometimes turned into torrents by desert cloudbursts. At such times, they became muddy and left sand and silt among the lime deposits which were accumulating on the bottom of the lake. When the lake drained away, these deposits were exposed to erosion—the clay and silt were softer than the lime and eroded more rapidly leaving irregular cavities and caves of all sizes. It is in one of these caves that the Indians built Montezuma Castle. Today the pitted and jagged surface of the cliff appears like crumbling limestone. In places it is so soft it can be removed by the pressure of a finger. After the ancient lake drained, rain and melting snows from higher elevations continued to find their way into the valley where the water seeped below the ground, dissolving the limestone as it went. Underground river channels and caves were slowly formed by this water. One such channel, leading from a cave, was eventually cut through from the surface by the eroding waters of Beaver Creek. This allowed the water in the underground cave to pour out into the creek. The roof of the cave, weakened by the removal of this water and by solution cracks forming from the surface, soon collapsed to form Montezuma Well as it is seen today. It is due to this action that the Well is technically referred to as a limestone sink. Thus the slow, but powerful forces of earth shaped the Verde Valley into a congenial environment for man. _Man in the Verde Valley_ The first human occupation of central Arizona began several thousand years ago. Very little is known about these Indians, but there is archeological evidence which indicates that they were hunters and food gatherers. These people had no pottery, and probably had no permanent houses or farms. The only objects recovered from their campsites have been their crude stone tools. One such site was discovered and investigated a short distance north of Montezuma Castle National Monument in 1949.