The San Juan-Cascade (SJC) nappes were subducted to a depth of ~18 km, metamorphosed under low-temperature, high-pressure conditions, and then exhumed, all within ~16 m.y. During exhumation, penetrative deformation by solution mass transfer (SMT) resulted in a widespread spaced cleavage. Strain directions were determined for 27 sandstone samples, and absolute strain measurements for a subset of 19 samples. Z directions generally plunge moderately to the NE, and X and Y directions are scattered in the plane perpendicular to Z. SMT deformation is constrictional at the local scale, but the tensor average indicates plane-strain uniaxial shortening at the regional scale, with Sx, Sy, and Sz equaling 1.01, 0.91, and 0.58, respectively. The average flattening plane (XY) dips 30¿ to the NE, and the average X direction plunges 20¿ to the north. The large shortening in Z was compensated by a mass-loss volume strain of ~47%. We present a simple one-dimensional model that illustrates the relationship between finite strain and ductile exhumation for a steady state convergent wedge. Assuming depth-dependent ductile flow and no reversal of principal strain rates with depth, this model indicates that ductile thinning of the SJC nappes accomplished only 13% of the total exhumation, despite a vertical shortening strain of 36%. There is no evidence that normal faulting contributed significantly to exhumation. We conclude that erosion operating at an average rate of ~1.1 km m.y.-1 was the dominant exhumation process. ¿ 1999 American Geophysical Union