The Funeral Mountains of the Death Valley region consist of a metamorphic core complex that underlies the Miocene Boundary Canyon detachment fault. Fission-track age determinations on sphene, zircon, and apatite from the highest grade portions of the Funeral Mountains (collected in Monarch Canyon) indicate rapid cooling from above ~285 ¿C at 9--10 Ma. The steep dT/dt slope implied by the cooling path envelope as well as its synchroneity with development of the Boundary Canyon detachment suggests tectonic unroofing of between 9.5 and 17 km since ~10 Ma (assuming typical geothermal gradients prior to detachment development of between ~20--30 ¿C/km). Previous studies report muscovite 40Ar/39Ar plateau ages from the same area indicating that the Funeral Mountains core may have cooled below ~350 ¿C between 110--55 Ma. These data, when combined with the fission track ages, suggest residence of the metamorphic terrain at 285--350¿C from Late Cretaceous to late Miocene time. Recent studies, using petrologic contraints, have suggested that much of the unroofing of the Funeral Mountains, as well as development of tectonite fabrics, occurred during Mesozoic extension. Recognition of temperatures in the 300 ¿C range during Miocene time suggests some of the ductile extensional fabric may be late Miocene in age. ¿American Geophysical Union 1991