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The M7.9 2002 Denali earthquake, Alaska, is one of the largest strike- slip earthquakes ever recorded. The postseismic GPS velocity field around the 300- km- long rupture is characterized by very rapid horizontal velocity up to similar to 300 mm/ yr for the first 0.1 years and slower but still elevated horizontal velocity up to similar to 100 mm/ yr for the succeeding 1.5 years. I find that the spatial and temporal pattern of the displacement field may be explained by a transient mantle rheology. Representing the regional upper mantle as a Burghers body, I infer steady state and transient viscosities of eta(1) = 2.8 x 10(18) Pa s and eta(2) = 1.0 x 10(17) Pa s, respectively, corresponding to material relaxation times of 1.3 and 0.05 years. The lower crustal viscosity is poorly constrained by the considered horizontal velocity field, and the quoted mantle viscosities assume a steady state lower crust viscosity that is 7 eta(1). Systematic bias in predicted versus observed velocity vectors with respect to a fixed North America during the first 3 - 6 months following the earthquake is reduced when all velocity vectors are referred to a fixed site. This suggests that the post- Denali GPS time series for the first 1.63 years are shaped by a combination of a common mode noise source during the first 3 - 6 months plus viscoelastic relaxation controlled by a transient mantle rheology.