This paper is a test of the use of symmetry analysis of basket design to measure interaction among northern and central California Indian cultures. Although long-distance trade networks and casual exchanges at ceremonies have long been known as vehicles for cultural interchange, anthropologists have not systematically used criteria other than language for studying affiliations. Differences in language classically have been used to define tribal entities, but the subsequent consideration of other cultural information within these linguistic units has masked the fact that much information and actual interaction crosses these "unintelligible" boundaries.