WASHINGTON (AP) - Chocolate for your sweetheart this Valentine's Day? Folks may be surprised to know how far back chocolate goes - perhaps 1,000 years in what is now the United States. Evidence of chocolate was been found in Pueblo Bonito in Chaco Canyon, N.M., the earliest indication of the tasty substance north of Mexico, Patricia L. Crown of the University of New Mexico and W. Jeffrey Hurst of the Hershey Center for Health and Nutrition report in Tuesday's issue of Proceedings of the National Academy of Sciences.

Drinking chocolate was associated with a variety of rituals in ancient Central America, including weddings, but Crown said she is not sure of its exact uses in her area.

The discovery, dated to between A.D. 1000 and 1125, indicates trade was under way between the Chaco Canyon residents and cacao growers in Central America.

But the nearest cacao plantation would have been more than 1,000 miles away, so importing the material would have been a major undertaking, she said. Chocolate was probably something not consumed often, she said in a telephone interview.

It also probably tasted bitter compared with what is available today. Central Americans didn't sweeten their chocolate and sometimes mixed in hot peppers. Crown said honey might have been available in new Mexico but she didn't know if it was used.

The research was prompted by a discussion about cylinder jars, when Crown was told the Maya used the jars for drinking chocolate.

She had pieces of ceramic that appeared to come from similar jars, so she had them tested for residue. There was theobromine, an indication of chocolate.

"This illustrates the importance of collections in archaeology," Crown said, "that we can return to material with new techniques and find out new things. Every artifact has a story to tell."

Chocolate was used in rituals in Central America as early as 1500 B.C. and was even a form of currency among the Aztec.

The new research was supported by the National Science Foundation, National Geographic Society, University of New Mexico and the Hershey Technical Center.

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