The Salmon River suture zone in west central Idaho juxtaposes volcanic arc rocks of the Wallowa terrane directly against cratonic North America. Detailed metamorphic studies along a 10 km traverse perpendicular to the suture indicate that the arc and two crystalline fragments thrust upon it each record different pressure‐temperature (P‐T) histories. From lowest to highest structural level: the Wallowa terrane shows only subgreenschist metamorphism, the Rapid River plate (RRP) records unroofing and cooling from ∼8 kbar and 550°C to 6 kbar and 475°–500°C, and the Pollock Mountain plate (PMP) shows evidence for polymetamorphism and records burial and heating paths to final equilibration conditions of 9–11 kbar and 600°–625° C. Ar‐Ar hornblende ages combined with the P‐T data suggest that currently exposed levels of the RRP and PMP were juxtaposed against one another at 15–20 km depth at or prior to 118 Ma, indicating that 10–20 km of uplift, and hence also the onset of collision‐related metamorphism, occurred before ∼118 Ma. Correlation of the metamorphic and age data with geometric constraints from the initial Sr 0.706 line and the dimensions of the RRP and PMP permit construction of large‐scale retrodeformable sections of the west side of the suture from Late Jurassic through Late Cretaceous time. The abrupt nature of the Sr 0.706 line implies that the arc‐continent boundary extends vertically through most of the crust, which requires sharp downwarping of the arc lithosphere in order to account for the PMP metamorphic data. Narrow zoned overgrowths on PMP garnets record this burial event and require initially rapid (≥3 km/m.y.) uplift rates in order to be preserved. We suggest that the onset of rapid uplift resulted from the separation of the negatively buoyant lithospheric root from the downwarped arc, allowing buoyant rise of fragments of thickened crust. Detachment of the root is suggested to change the environment of crustal shortening from one in which footwalls of thrusts or shear zones sink to one in which hanging walls rise. This mechanism represents an alternative to cessation of shortening or onset of tectonic denudation as an explanation for the transition from burial to uplift of high‐pressure metamorphic terrains. Subsequent uplift appears to have been slow and to have occurred in a hinged fashion such that mineral and whole rock ages decrease systematically towards the suture zone. The consumption of lithosphere during ≥40 km of shortening between two crustal blocks implies that the Salmon River suture is the trace of an intracontinental subduction zone. Burial and collision apparently began before about 130 Ma, and thus any precollision strike‐slip faulting or tectonic escape of intervening terranes was likely accomplished