A recently obtained isotopic cooling curve for the Quottoon pluton, near Kitimat, British Columbia, has allowed resolution of its thermal history. Our analysis is based on a time-dependent mathematical model of the cooling of a two-dimensional pluton with rectangular cross section. The pluton is assumed to be intruded into a medium initially in equilibrium with a constant geothermal flux and evenly distributed radioactive heat sources. A complicated history of regional uplift can be assumed. Model input parameters constraining dimensions, thermal properties, thermal flux from the mantle, heat production, uplift rate, and initial temperature were either measured or estimated independently of the numerical simulation. The cooling curve generated by our model agrees closely with the experimental curve derived from nine mineral dates and previously assigned values for closure temperatures of the radiometric systems. This approach appears to provide a valuable tool for calculating thermal effects of intrusion and for testing the physical soundness of geological interpretations.