  Montezuma Well and the cave in which Montezuma Castle is built both exist today because of a series of events that began over 1 million years ago. A flow of lava coming from the Black Hills at the south end of the Verde Valley closed the narrow canyon through which the Verde River then ran. This formed a natural dam and the river backed up against it to form a lake. Other rivers farther upstream added more water, and carried in large quantities of dissolved limestone from the higher elevations which they drained. Bird’s-eye view of Verde Valley landscape and geology. Consequently, in late Pliocene times (perhaps 1 million years ago), the Verde Valley was covered by a shallow lake or marsh 25 to 40 miles long and 12 to 15 miles wide. Its extent can be determined by noting the boundary between the light-colored sedimentary limestone and the dark basalts or the red sandstone marking the old shoreline. This light-colored rock was redeposited from the original limestone beds upriver and, therefore, the entire formation is almost devoid of fossils. Well preserved cougar tracks, however, imbedded in a slab of limestone, were found a few miles north of Montezuma Castle near Cornville, Ariz. 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 Thus the slow, but powerful forces of earth shaped the Verde Valley into a congenial environment for man. |
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