A reversed seismic refraction profile extending 260 km between Globe, Arizona and Tyrone, New Mexico has been recorded using quarry blasts from open pit copper mines as energy sources. Interpretation of these data suggest a 28-km-thick crust for the Basin and Range in east-central Arizona and a 32-km-thick crust for the Transition Zone in eastern Arizona and western New Mexico. Delays in Pn arrivals have been interpreted as evidence for approximately 4 km of abrupt crustal thickening near Morenci, Arizona. The area of abrupt Moho offset corresponds to rapid changes in tectonic style, late Quaternary faulting, Quaternary and late Tertiary volcanism, high heat flow and evidence for partial melting of the lower crust. Uniformity of layer thickness along the profile can be interpreted as upward displacement of the Basin and Range relative to the Transition Zone. The above evidence suggests that the Transition Zone of eastern Arizona and western New Mexico may be experiencing active tectonic readjustment.