This is a detached portion of the Montezuma Castle National Monument
Sink Hole –
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About 12 million years ago (the Tertiary) this area was covered by
a shallow lake. Plants that grew in the lake caused dissolved
calcium carbonate to precipitate out of the lake to form a soft
limestone at the bottom of the lake. This limestone is now known as
the Verde Formation.
About 2 million years ago the climate changed enough so that the
lake dried up. Then infiltrating precipitation and ground water,
which are slightly acidic, began dissolving the limestone to form a
cavern. At some point, the cavern grew so large that it could no
longer support the weight of the rocks above it and collapsed
forming the sinkhole. The water continued to dissolve the limestone
forming the side cave that drains the lake, called the Montezuma
Well.
The water entering the well is loaded with dissolved calcium
carbonate from its travels through the limestone beneath the
surface. When the water reaches the atmosphere, the dissolved
calcium carbonate precipitates back into limestone and releases
carbon dioxide. As a result the water in the well is extremely high
in carbon dioxide.
Swallet
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Water has dissolved cracks in the limestone that drain the well.
These cracks go from the side of the sink about 150 feet to the
side of the cliffs. It takes about 7 minutes for water to go
through the cracks to its outlet by the creek. The Native Americans
took advantage of this outlet and built a canal to irrigate their
crops.