Approximately 3000 middle and late Cenozoic nearshore marine molluscan taxa from western California are assigned to six time periods, spanning ~25 m.y. In this interdisciplinary study, western California is palinspastically restored for each of the time periods by backsliding and back-rotating large fault blocks or crustal units. Marine fossil assemblages are assigned to nearshore paleoclimatic regions or water masses within palinspastically restored California. In addition, this volume reveals positive feedback mechanisms between paleolatitudinal changes in sea-surface paleotemperature gradients and changes in the diversity of marine mollusks along the California coast through time; defines "equable" based effective temperatures; and analyzes extinction rates among macroinvertebrate marine taxa from coastal California and the possible causes of these extinctions. The late Paleogene to Neogene faunas reflect an increase in faunal diversity related to strengthened temperature gradients, greater extremes in sea-surface temperatures, reduction in temperateness, and the development of an embayed California coastline.