A little bit more info on the monolith found in Mexico city of a figure representing the rain god Tlaloc and another unidentified figure are carved into a frieze on the altar.

I just read this from Crystal links:
The god of civilization and learning) - 'Quetzal (feather) serpent," had dozens of associations.
It was the name of a deity, a royal title, the name of a legendary priest-ruler, a title of high priestly office. But its most fundamental significance as a natural force is symbolized by the sculpture of a coiled plumed serpent rising from a base whose underside is carved with the symbols of the earth deity and Tlaloc.

The image of the serpent rising from the earth and bearing water on its tail is explained in the Nahuatl language by a description of Quetzalcoatl in terms of the rise of a powerful thunderstorm sweeping down, with wind raising dust before bringing rain.