Obsidian from the Cow loeality, Inyo County, California. has long been regarded by archaeologists as a single "source." However, studies by the US. Geological Survey have provided evidence of geochemical variability among flows within the volcanic field. To determine whether these geochemical distinctions could be applied productively to archaeological research. nondestructive x-ray fluorescence analyses were conducted on samples recently collected from 15 obsidian-bearing loci. The results of this research show that geochemically distinct varieties of artifact-quality obsidian can be recognized within the Coso volcanic field, and subsequent nondestructive x-ray fluorescence analyses of artifacts from two nearby archaeological sites document that different geochemical varieties of obsidian were used prehistorically to manufacture twls. Implications of these results for studies of prehistoric exchange and obsidian hydration dating are discussed.
BACKGROUND
Malcom Fanner (1937) first reported an obsidian quarry near Coso Hot Springs in Inyo County, California (see Heizer and Treganza, 1972) and Mark Harrington (1951) conducted limited investigations a t a Coso locality he termed a "colossal quarry," but it was the work of Robert Jack that introduced the Coso area to a wider audience of archaeologists and obsidian specialists. Jack's work largely shaped the prevailing view of what the Coso source "is" and how it currently is being used archaeologically.
In his earliest paper on the area, Jack (Jack and Carmichael, 1969:31) specified that his obsidian collection was made at Coso Junction from an "extrusion south of ruined house east of U.S. Highway 395, Sect. 12, T22S. R38E, MDBM." Recent field inspection of this particular area failed to identify a primary outcropping of obsidian-rather, the area appears to represent a sec- ondary depositional context, potentially including a mixture of obsidians redeposited from primary deposits to the east. While it was clear that Jack