Yes it is true! Recent research shows that folks in southern Mexico, from the years ~500AD to ~1000AD at least, traded their chocolate for what they didn't have: copper in the form of turquoise. The turquoise came from parts of what is now the southwestern USA. Archeologists made the linkage after recently finding traces of chocolate in ancient vessels in New Mexico. For some time now, the archeological community has known that turquoise objects found at Chichén Itzá have the unmistakable chemical fingerprint of copper deposits located in New Mexico, Arizona and Nevada.
It begs the question,why would the Arizona miners of yore have given up their metallic patrimony? Did this "extractive industry" leave them with nothing while all the rich foreigners (Mayans in this case) got their riches? This isn't the spin that the archaeologists or anyone else leaps to put on it. Clearly the folks in New Mexico liked chocolate (duh), a crop they did not grow. At the same time the turquoise, much valued by the Mayans, did not occur in their backyard. (Nevertheless we feel compelled to point out that the chocolate must have been highly prized. Metal, being eternal, has preserved the Mayan artifacts while the chocolate consumed by the ancient Arizonans has long ceased to fertilise the soil.)
Thank goodness the earth varies geologically. Every part of the earth has different geologic riches to offer. Canada mines and trades to others its nickel, a metal that Mexico is almost devoid of. Yet Mexico is uniquely rich in silver and provides the world that special commodity. Why is it this simple phenomenon subject to 100 year old political spin? Why is that view gobbled up? We should be very glad that the earth is variable. While there are always people, like the Spanish conquistadors, who chose to steal other peoples possessions through aggression and conquest, geological variety can foster peaceful exchange which is a win-win way to get what you want. You gotta give to get, so figure out what you can give. That is clearly what the old timers thought, at least some of the time.