High topography in central Asia is perhaps the mostfundamental expression of the Cenozoic Indo-Asian collision, yet an understandingof the timing and rates of development of the Tibetan Plateau remains elusive.Here we investigate the Cenozoic thermal histories of rocks along the easternmargin of the plateau adjacent to the Sichuan Basin in an effort to determinewhen the steep topographic escarpment that characterizes this margin developed.Temperature-time paths inferred from 40Ar/39Arthermochronology of biotite, multiple diffusion domain modeling of alkalifeldspar 40Ar release spectra, and (U-Th)/He thermochronologyof zircon and apatite imply that rocks at the present-day topographic frontof the plateau underwent slow cooling (30¿--50¿C/m.y.)coincident with exhumation from inferred depths of ~8--10 km, atdenudation rates of 1--2 mm/yr. Samples from the interior of the plateaucontinued to cool relatively slowly during the same time period (~3¿C/m.y.),suggesting limited exhumation (1--2 km). However, these samples recorda slight increase in cooling rate (from <1 to ~3¿C/m.y.) at sometime during the middle Tertiary; the tectonic significance of this changeremains uncertain. Regardless, late Cenozoic denudation in this region appearsto have been markedly heterogeneous, with the highest rates of exhumationfocused at the topographic front of the plateau margin. We infer that theonset of rapid cooling at the plateau margin reflects the erosional responseto the development of regionally significant topographic gradients betweenthe plateau and the stable Sichuan Basin and thus marks the onset of deformationrelated to the development of the Tibetan Plateau in this region. The presentmargin of the plateau adjacent to and north of the Sichuan Basin is apparentlyno older than the late Miocene or early Pliocene (~5--12 Ma).