Numerous indigenous groups have inhabited the high plateau region of the Trans-Mexican Volcanic Belt (also known as the Cordillera Neovolcánica) and have done so for several millennia.

Among these groups are the Otomi, considered by some historians to be the earliest inhabitants of the Valley of Mexico, who were eventually displaced eastward by other groups like the Nahua. The Otomi are linguistically related to other Uto-Manguean speaking peoples, including the Mazahua, Matlatzincas, Tlahuicas, and Chichimecas.

In the pre-Hispanic era, various groups like the Olmec, Izapa, Teotihuacan, Maya, Zapotec, Mixtec, Huastec, Purepecha, Totonac, Toltec, and Aztec flourished in different parts of the Mexican region.

The Otomi are an indigenous people of Mexico who inhabit the central Mexican Plateau region and are linguistically related to the rest of the Uto-Manguean speaking peoples which is a division of the Uto-Aztecan family group and ultimately a member of the Nahuatl family and descentant of the Sons of Nahatl.

Mexico City, or otherwise called the Valley of Mexico was built upon the ruins of Tenochtitlán, which was the capital of the Aztec Empire. Over the millennia the inhabitants of the Valley of México have included the ancient Aztec (Mexica), Toltec and Chichimeca tribes, cultures which left a wealth of relics and ruins in the area that continue to attract and amaze moderns. Most of those who lived in the Valley of Mexico were of the Náhuatl speaking languages including: Tenochtitlán, Acolhua of Texcoco, and Chalca of Chalco.

The Lerma River is the second longest river in Mexico, about 470 miles in length and traverses the southern area of this ecoregion along much of the northern Michoacan state line. The river begins not far west of Mexico City in the Sierras de Volcanic Mountains and flows west by northwest through most of it′s length.

The source of the Lerma River is at Almolya del Río, a town and municipality located in the State of Mexico 26 km from the state capital of Toluca. The name Almoloya comes from the Nahuatl phrase almoloyán which means place where water flows out. "del Rio" means "of the river" in Spanish and refers to the Lerma River, which originates here. The source is at 9,843 feet above sea level.

The mouth of the Lerma river is located near to the city of Guadalajara, Jalisco, at the eastern edge of Lake Chapala, (the largest lake in Mexico) and is found at 5000 feet in elevation.

The source of the Santiago River is Lake Chapala, unless you consider it part of the Lerma River. From Lake Chapala, it flows 270 miles northwest and enters the Pacific ocean from the state of Nayarit about 70 miles north of Puerto Vallarta, Jalisco.