Copper metallurgy appeared suddenly in West Mexico around 900 A. D., from where it spread relatively rapidly to other parts of Mesoamerica. Since metallurgy in the Andean predates Mesoamerican metallurgy by over a millennium, it is possible that metallurgy arrived in West Mexico by diffusion from the Andean area. Metallurgy also occurs earlier in the intermediate area (Columbia and Panama) than in Mesoamerica, but copper was only used to make a gold-copper alloy known as tumbaga. A comparison of West Mexican and South American copper artifacts is undertaken in order to determine whether West Mexican versions may be the result of direct trade with South America. Of 10 classes and 15 types or subtypes known from West Mexico around 900 A.D., all 10 classes and 11 types or subtypes have direct parallels in copper artifacts from South America. Of 6 new classes and 17 types or subtypes introduced from A.D. 950 -- A.D. 1000, only two new classes and four new types or subtypes have specific parallels in South America. The sudden appearance of copper metallurgy in West Mexico and its initial close parallels with South American traditions argue in favor of direct diffusion of the technology. An exchange network linking the central coast of Peru, the Guayas Basin of Ecuador and west Mexico is postulated based on the distribution of artifacts included in the study. The West Mexican products exported to South American are unknown, but peyote is one possibility.