One possible arrangement is multiethnic procurement at a geological source. Ericson (1982: 136) describes a situation in California's Napa Valley where the Saint Helena obsidian source fell within the territory of the Wappo ethnic group and the Wappo were, in turn, surrounded by the Lake Miwok, Coast Miwok, Wintun and Pomo groups (Kroeber 1925). It is reported that in exchange for obsidian, the Wappo received items such as bows, beads, shells, mats, fish, headbands, and clams (Davis 1961), but it is not known if extraction was conducted by the local Wappo or through direct access by the surrounding groups themselves. Ericson (1984: 7) reviews evidence of multiethnic access to lithic sources. In California there are a number of distinctive obsidian sources that have been studied. At some areas the quarry management was "tribal but related and nearby groups had the right to quarry either freely or on the payment of small gifts. Wars resulted from attempts by some distant tribes to use a quarry without payment. On the other hand, the Clear Lake obsidian quarries were neutral ground" (Bryan 1950: 34).

The Wintun of California practiced round-trip fasting when traveling to obsidian sources (Dubois 1935). A functional interpretation of this behavior from Ericson (1984: 7) is that fasting would avert exhaustion of resources around much-visited obsidian sources. A regionally important quarry could conceivably get so much use, with many groups exploiting the source, that the ecology of the source area catchment would get depleted.

Geochemical studies of obsidian artifacts in California have revealed a concordance between obsidian distributions, as shown by chemical studies, and the geographical boundaries of ethnographically documented cultural groups (Bettinger 1982;Hughes and Bettinger 1984;Luhnow 1997). Dillian (2002: 294-297) found that despite ethnographic accounts of Karok direct procurement at the Glass Mountain source in Modoc territory, the knapping evidence at the source suggests that local Modoc were conducting virtually all of the reduction on site and then exchanging with neighboring tribes where it was widely circulated.