In many respects, the people of Emeryville were self-sufficient from the earliest times. The rich natural resources of the local environment supplied virtually all that they needed in the way of food and materials to manufacture shelter and tools. Nonetheless, even the earliest occupants of Emeryville had ties with other groups in the Bay Region and probably throughout California. The Emeryville Shellmound provides archaeological evidence of trade and other interactions among these groups throughout prehistoric time.

Shell Artifacts
It is not uncommon to find abalone shell artifacts manufactured from Pacific Coast shells in archaeological sites in western Nevada. Projectile points ("arrowheads") of obsidian (volcanic glass) from Napa, Sonoma, and as far away as the eastern Sierra Nevada are present in most prehistoric sites in the San Francisco Bay Area. Most likely a Paiute Indian did not make a 600 mile trek to the Pacific Ocean to collect the abalone, nor did the coastal people routinely travel to the Sierra Nevada for obsidian. Probably these valuable materials were exchanged by trading through intermediate groups. In an archaeological assemblage, it is possible to identify exotic items (those materials that were not available locally) and study the ways in which these materials were traded.

Sources of Traded Materials
We often can identify the sources of the traded materials. For obsidian, this is relatively easy, as each source has a distinctive chemical "fingerprint", through which artifacts can be traced to their specific source. The sources of shell ornaments may be identified on the basis of the natural habitat in which the shellfish lives: for instance, abalone live in rocky intertidal zones, and do not grow in the shallow parts of the San Francisco Bay, so they had to be obtained in trade with coastal groups. For artifacts that arrived ready-made at their trade destination, it may be possible to identify trade sources based on artifact types or styles found in common between archaeological sites in different regions. For instance, a certain style of abalone ornament found inland (say a teardrop shape with a single perforation) also may be common to certain coastal groups. This might help identify the groups that were trading.

Raw vs. Finished Goods
In some cases, exotics were traded as bulk raw material; in other cases, the materials may have arrived at their destinations as finished tools or ornaments. Obsidian appears to have arrived in both forms at Emeryville, but it is not found in large pieces, and it clearly was a valuable material. Broken artifacts were reworked and reused, and waste fragments discarded during manufacturing are quite small. Abalone clearly arrived at Emeryville as ready-made ornaments, and not as raw material. There is virtually no abalone shell among the dietary waste, and no evidence of manufacturing debris. Further, it is clear that abalone ornaments were considered valuable, as almost all the specimens from the site were found in graves.

Exchange of Goods
Identifying what was given in exchange is a greater challenge. Shell beads and ornaments commonly are found in archaeological sites throughout much of California. During historic contact times, the Ohlone people of the Bay Region are known to have traded shell ornaments to the Yokuts of the San Joaquin Valley and the Central Miwok who lived in the Sierra foothills. In exchange they may have received obsidian, pine nuts or other inland resources to which inland groups had access or would serve as intermediaries. Groups on the bay who did not have direct access to abalone shell could have served as intermediaries to trade with inland groups, and obtained abalone from coastal groups in exchange.

Origins of Obsidian
Not surprisingly most of the obsidian found at the Emeryville Shellmound came from sources in Napa Valley - the closest location from which obsidian could be obtained. However a few samples came from a much greater distance on the east side of the Sierra Nevada mountains. Almost all of the obsidian artifacts from these more distant sources are either complete or fragments of finished artifacts (projectile points and knives). This suggests that the "cost" of obsidian from these remote sources was high and/or that it was relatively more difficult to obtain. Trade almost certainly would have involved intermediary groups, who would add to the cost of the trade goods.
An archaeological site also provides an opportunity to study the ways that trade changed through time. We may be able to identify changes in trade patterns through time by observing the changes in obsidian projectile point types and shell ornament types through time, and correlating these changes with the dated layers and features of the site. In some Bay Region sites, for instance, we can see changing proportions in the use of obsidian from the Sierra relative to obsidian obtained from the Napa region. We also can recognize changes in preference for certain materials. For instance, in the early occupation of Emeryville, cutting tools often were made of chert, a locally available rock. Later, obsidian, which had to be obtained from a distance but which could be worked to a razor sharp edge, became more common. These changes may reflect the discovery of new technologies (sometimes adopted from trade partners), or they may reflect changes in political control of an area, or changing alliances among groups with differing access to traded materials.