The Galápagos Islands have long fascinated biologists because of their numerous endemic species—that is, kinds found no place else. Indeed, the unique life forms of these Pacific islands helped give rise to the theory that makes sense of such phenomena.
Our Chihuahuan Desert has its own "Galápagos Islands"—Cuatro Cienegas. This naturally closed, intermountain valley in central Coahuila is famous among biologists for its numerous endemcs—more than 70 plants and animals found nowhere else—plus an amazing diversity of other organisms.
To a considerable degree, this wealth is made possible by hundreds of
geothermal springs, lakes, and streams—thus the name, which means "four
marshes". These provide permanent homes for aquatic organisms and great
opportunities for evolving isolated from each other. The overall environmental
stability of this bolson has allowed it to act as a refuge for those managing to reach
it. Thus, during the Ice Ages, some species from the east were able to reach the
valley. They became marooned in these marshes as surrounding areas warmed up and dried
out.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
Very good background; with a map link.