The Brazil Mound Page 20

This large obsidian blade was one of four found together at the Brazil Site. It probably dates to the Middle Prehistoric Period.

of California and had to be brought here from somewhere else. Obsidian is a volcanic glass that was made into tools and ornaments by prehistoric people throughout most of California and the western United States. Because it is a glass, obsidian forms a very sharp edge when broken; these sharp tools were used for tasks that required cutting, scraping, and piercing. Obsidian also was made into points for arrows, darts, and spears. Because of its many uses, and perhaps also because it can be quite beautiful, this raw material was highly valued by Native Californians.

Today, obsidian is a valuable tool for the archaeologist, as well. For one thing, obsidians from different volcanic sources usually have different chemical signatures; that is, the ratios of certain chemical elements in the glass vary from one source to another. For example, obsidian from the Napa Valley in west-central California has significantly more zirconium, and significantly less strontium, than obsidian from Bodie Hills, on the east side of the Sierra Nevada. By comparing the ratios of these and other chemicals, the archaeologist can determine where a particular piece of volcanic glass originated.

Obsidian from both the Napa Valley and Bodie Hills was found in the flaked stone collection from CA-SAC-43, although Napa obsidian was much more common than Bodie Hills. This suggests that the prehistoric occupants of the Brazil Mound had access, either through travel to the source or through trade with other groups, to both kinds of obsidian, but that their ties to the west may have been stronger than their ties to the east.

Was this stronger tie to the west always true, or did the Brazil Mound people trade with different neighbors during different periods of time? In our own era, we have seen many changes in the alliances between countries. For example, Germany and the United States are strong allies and trade partners today - just consider the number of German cars on American roads - but a few decades ago, the two countries were at war, and no products were traded between us for many years. Archaeologists assume that such changes also took place in prehistoric times.

Ground and Battered Stone Tools

The people who lived at the Brazil Mound during prehistoric times probably ate a variety of

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