Extant codices depict Aztlan as an island surrounded by water and locate it somewhere to the far north of the Valley of Mexico.
The name "Aztlan" appears to refer to a land populated by the white heron, the egret or the crane although some other etymologies have been suggested. The texts describe Aztlan as having many different types of waterfowl and also describe the area as a 'place of reeds.' The description seems to indicate that the fabled homeland was a marshy stopping place of migratory aquatic birds.
According to Sahagun, the people of Aztlan called themselves the Chichimecas "Dog People," or Atlcachichichmecas "Fisher-Folk Chichimecas from a Far Country."
Clavijero writes of the tradition of the azquahuitil tree on which is found a bird making the tihui sound. According to their histories, the Aztecs began their migrations from Aztlan at the prompting of this bird and were led by Huitzilopochhtli "Hummingbird of the South" also known as Mexi, whence Mexicas or Mexicans. These migrations are variably dated usually between the 7th and 11th century CE.
Competing theories have located Aztlan in many different regions north of the Valley of Mexico including various spots in northern Mexico, the American Southwest, California, Florida and Wisconsin. The available geographical information makes it difficult to identify the location with any precision.
However, there is an interesting geographical tradition that arose when the Spanish arrived that might be related to the concept of Aztlan as an island.
For at least a century, and for probably longer, European geographers represented California as an island.
In the earliest forms of this representation, it appears that the old isle of Zipangu, mentioned by Marco Polo, was conflated with Aztlan traditions and depicted as an island off the west coast of North America where California should be located.
Later in the early 1600s, this island was given the name "California," a name of confused origins.
Map of California as an island by Joan Vinckeboons, ca. 1640.
It may be that the Spanish took descriptions of Aztlan as a paradise homeland of the Aztecs as reference to their own Eden, which in medieval European minds was associated with the region around Zipangu, a land of spice forests.
The first known mention of California in the 1510 romance novel Las Sergas de Esplandián by Garci Rodríguez de Montalvo also associates the land with biblical Eden:
Know, that on the right hand of the Indies there is an island called California very close to the side of the Terrestrial Paradise; and it is peopled by black women, without any man among them, for they live in the manner of Amazons.
The description above is of an island in the East Indies, like Zipangu, in this case the medieval "Island of Women." The Spanish began to refer to the new discoveries of Hernán Cortés in Baja California as "California" in the early 1540s possibly taking into account the legends of the original homeland of the Mexica.
Paul Kekai Manansala
Smith, Michael E. "The Aztlan Migrations of the Nahuatl Chronicles: Myth or History?". Ethnohistory, 1984.