Montezuma Well is a unique geological feature providing a constant source of water in the midst of a desert environment. The Well may have been visited by the Spanish as they entered the Verde Valley in the late 16th century. It received its name from Anglo pioneers who noted the similarity of the cliff dwellings located under the rim of the Well to the structures seen in Mexico attributed to the Aztecs. Geologists have estimated the age of the Well at approximately 10,000 years. Springs, rich in dissolved travertine, bubbled up, creating a dome over eons which eventually collapsed as the water flowing underground dissolved the support structures of the dome. Two older travertine domes formed long before the latest dome which formed the Well. The first dome was much greater in size, being almost a mile in diameter. The edges of this dome can be seen on the south side of Wet Beaver Creek and on the north side of the county road that passes through the monument. This northern edge was commercially mined during the 1950's for the travertine, which, when cut, resembles marble. The second dome was approximately one-half mile in diameter. A remnant of this dome forms the highest point in the Well Unit, located to the north of the sinkhole.
The waters flowing into the Well are unique also. Flowing out at a constant temperature of 74 degrees fahrenheit from vents deep beneath the surface, the water is heavily-laden with travertine, carbon dioxide, and arsenic and supports over 100 kinds of invertebrates, four of which occur nowhere else in the world: an endemic amphipod (Hyallela montezuma), an endemic leech (Motobdella montezuma), a water scorpion (Ranatra montezuma), and a snail (Pyrgulopsis montezuma). At the base of the food chain is the amphipod, a shrimp-like creature. Next on the food chain is the leech, which searches for the amphipods during nighttime hours, using hair-like filaments to find its prey. At the top of the food chain is the ranatra, which preys on both the leeches and the amphipods. Due to the extremely high amount of carbon dioxide (over 200 times the amount in tap water) no fish can survive in the Well. The high arsenic level of 100 parts per million further limits the ability of the water to support other forms of aquatic life. Because of these unique conditions, several research projects are on-going at the Well, which has been called one of the most productive ecosystems in terms of biomass production. Illinois pondweed (Potemogoten illinoiensis) rings the shoreline of the Well, growing to a length of 8-10 feet. The pondweed can be found throughout much of North America, but usually only attains a height of 6-8 inches.
The water flowing into the Well is estimated to originate high on the Mogollon Plateau over 30 miles to the east. Due to the size of the acquifer, there is very little fluctuation in the amount of water flowing into the Well, which has remained constant at approximately 1.5 million gallons daily. This water has found an outlet at the swallet (where a stream disappears underground) and emerges 150 feet later on the creek side of the Well where it was channeled into a ditch by the prehistoric inhabitants to irrigate agricultural land. It is estimated that the water flowing from the Well carries almost 600 pounds of dissolved minerals per day, with approximately 200 pounds of minerals adhering to the sides and bottom of the ditch. Many miles of prehistoric ditches can be traced by the parallel lines of the hardened travertine.