Figure 9. Post–18 Ma (basin-range) paleotectonic map of the Great Basin and adjacent areas. Boundaries of Basin and Range Province and extent of magmatic arc are adapted after Dickinson (1997, 2002). Postarc volcanic centers (and local Late Miocene core complexes), formed near California-Nevada line in western Great Basin as Mendocino triple junction migrated northward (offshore arrow), not shown within span of earlier arc magmatism. Chain of Snake River Plain calderas (hachured circles with ages in Ma inside circles) of Yellowstone (Y) hotspot track (initiated with McDermitt caldera [M]) is modified after Pierce and Morgan (1992). Mid-Miocene Columbia River dike swarms (west to east): Monument, Cornucopia, Chief Joseph. Modoc-Oregon lava plateaus are largely Pliocene in age at the surface. Other features: BM—Blue Mountains; Gf—Garlock fault; NNR—Northern Nevada Rift (geophysical extent); StB—Steens Basalt (coeval with Columbia River Basalt).