Social capital is widely recognized as an important aspect of regional economies, and social networks in particular have recently been the focus of research in economic sociology and economic geography. Building on this body of work, this research explores the role of social networks in the divergent economic fortunes of two highly advance Californian metropolitan regions over the past three decades, Los Angeles and the Bay Area. Proxies for the two regions' industrial social structures are constructed and analysed at three cross sections over the divergence period: 1982, 1995 and 2010. Network analysis shows that the Bay Area's industrial social structure maintains a high level of connectivity, bridging relations across industrial boundaries, and by 2010 has a highly connected and central business-civic organization, the Bay Area Council. The LA region's social structure, on the other hand, fragments substantially over the period.