Cuatro Cienegas (Four Marshes) Biological Reserve is located in the State of Coahuila, in Mexico, specifically at the northern end of the Sierra Madre Oriental Mountain Range, in the eastern section of the Chihuahuan Desert (the largest desert in North America), in the Mesa del Norte "Northern Plateau" (whose boundary extends from the U.S. border sloping southward and upward between the Sierra Madre Occidental (to the west) and the Sierra Madre Oriental (to the east) to the southern boundary at the Zacatecas Mountains near the the ciudad of San Louis Potosi. This reserve is situated in a small (30. mi wide by 5-15 mile long, totaling 272 sq. mi.) intermontane valley (lying between the mountains, and refers to the basin formed by run-off sediments from the surrounding mountains). The 5 mountains that surrounds the valley are: Sierra de la Madera (9,842 ft.), Sierra de Menchaca (6,900 ft.), Sierra de San Marcos & Pinos (7,550 ft.), Sierra de la Fragua (7,220 ft.), and the Sierra la Purisima (7,220 ft.). The elevation of the basin averages 2,400 ft. above sea level. The basin has the greatest number (77) of endemic species (including flora and fauna) of any place in North America. The basin floor percolates with mineral water that is pushed upwards through hundreds of bubbling spring-fed pools of water (called "pozas"). The waters include thermal and cool springs, clear and turbid waters, fresh and saline. The waters are mainly enriched with calcium sulfate (gypsum), with lesser amounts of sodium, mangnesium, and chloride. The pools in Cuatro Cienegas vary from the largest which is 250 ft wide and 25 ft. at its deepest, to pools the size of small aquariums. The reserve consists of grasslands with aquatic, semi-aquatic, and gypsum-dune habitats within the basin and desert scrub and chaparral on the mountain slopes and oak-pine woodlands, and montane forests of pine, Douglas fir, and Arizona cypress on the upper altitudes of the mountains. This reserve is only 1 of 2 desert spring ecosystems of its size in North America. It is also one of Mexico's "13 National Wonders". This reserve is called "Mexico's Desert Aquarium" (which includes 30+ indigenous species of aquatic organisms). It is also called the "Galapagos of Mexico" also having 60 mammal species, 145 bird species, 60 reptiles, 8 amphibians, 17 fish species, and 883 vascular plants (77 that are endemic to the basin area). One of the main reasons for this trek was to experience the "Blue Moon"/"Luna Azul" (2nd full moon within the same month, which occurs about every 33 months) rising over the "Blue Pool"/"Poza Azul" within the Cuatro Cienegas Basin - Dec. 31, 2009 - a memorable New Year.