Chalco
This detail features a glyph for the place name Chalco, which the gloss explains as “the place of the precious stone.” The ending -co stands for the place of, and chal- is the root of chalchihuitl, precious stone in Nahuatl.
[Note: For another, similarly shaped glyph for Chalco, see this web page, http://geog.berkeley.edu/ProjectsResources/Glyphs/Plate11/Chalco.html.] [SW]