The people of the Columbia Plateau have been frequently characterized as a homogenous culture despite a 2,500-year depth of history and large spatial extent. Moreover, differences in artifact form, assemblage composition, and household features belie this characterization. The changing natural and social environment can be detected in modifications to technology, and relationships among distinct groups can be inferred. The research presented here considers these changes and asks: can the cultural learning and adaptive strategies of late prehistoric cultural groups be identified in the variability of southern Columbia Plateau projectile points? And, how does obsidian procurement reflect changing cultural interactions and exchange networks in the southern Columbia Plateau over the past 2,500 years? By using concepts from evolutionary and social network theories, this study employs obsidian provenience sourcing and the morphometric analysis of projectile points to trace the ways people dealt with these environmental and social pressures through shifting adaptive strategies and increased intergroup interaction. The investigation of projectile point form and obsidian source use in the southern Columbia Plateau largely supports the idea the people in this region maintained highly permeable social boundaries throughout the late prehistoric, but were not entirely homogenized. The picture is one of intense sub-regional connections; projectile point evidence from 35GM9/Wildcat Canyon, within the John Day- Deschutes-Dalles sub-region suggests a strong connection to the Lower Columbia River as well as the Lower Snake River, but more tenuous connection south into Oregon. Conversely, obsidian and projectile point data from site 35WH13/Indian Canyon, located further upstream on the John Day River, suggests a strong connection to central Oregon and Great Basin peoples. People in the Clearwater and Salmon River areas of the eastern Plateau eschewed interactions with groups of people in central Oregon and Washington in favor of maintaining strong connections in southern Idaho. Most significantly, it appears that the Lower Snake River area is home to a great deal of variability and diversity in both obsidian and projectile point form, hinting at a hub of intra- and inter-regional interaction akin to more famous ethnographically known trading areas such as the The Dalles.