Since Permian time geologists think the seas may have risen again and covered what is now New Mexico, leaving sediments that have been largely removed. About 60,000,000 years ago, during the Cretaceous period when coal was being formed elsewhere in the world and dinosaurs roamed the earth, the land was uplifted, perhaps producing cracks and crevices in the limestone.
Geologists at one time believed the Caverns were caused by the action of water as it flowed down through the limestone, dissolving as it did so minute particles of the stone. Today, however, that theory has been discarded, since a more careful and detailed study indicates the Caverns to have been formed by phreatic solution, their development resulting from a two-cycle method of creation.
The Caverns can be said to be a natural cavity in the earth formed by the solution of rock by subsurface waters. Actually, there are two great geological processes involved in the formation of the Caverns. The first came about as the water hollowed out the underground chambers, and the second took place when the formations of stone were created in these underground openings.
To be explicit, we can only say that the Caverns are large crevices or cracks in the limestone which have been enormously enlarged by the constant solution of the rock into the underground water which filled these indentations.
In order to understand just what the two-cycle method means and how it can exist, we must first understand the two conditions under which these operations of nature can take place.
Water, as it seeps downward into the earth, tends to seek what we shall call its own level. This would be a point where everything below is saturated with water, the water table of the region. Above the table water works downward due to its gravitational pull. Below the table there is only rather slow movement of water.
The area above this point is known as the vadose zone, and below this point the area is the ground-water or phreatic zone.
Any farmer who has ever sunk a well knows how important it is that his well reach below the water table if he is to be assured a continuous supply of water. Well owners also know that the water table can rise or fall due to any of several natural causes, such as an abundance of rainfall for a few seasons, or any great lack of rainfall for an extended length of time. When the water table goes below the lowest reaches of the well, no more water can be pumped, and it is necessary to extend the well further into the earth until it again goes below the water table and reaches into the saturated area where water is abundant.
The water table is not constant around the world, even though water seeks its own level. The water table might be high in one section of the country, low in another. It might be kept high by an abundance of rain, or remain low due to outlets such as springs or underground seepages.
The vadose-water area also varies, and the effects created by the rise and fall of the water table in one section of the country, for example, might be vastly different than the effects in an adjacent territory. This explains why any action of underground water in one area is not necessarily duplicated in an apparently identical area close by.