AbstractA rigorous analytical solution is developed for the lateral linear shear response of embankment dams in semi‐cylindrical valleys. Closed‐form algebraic expressions are presented pertaining to both free and base‐induced oscillations, and extensive parametric and comparative studies elucidate the prominent effects of canyon geometry (shape and aspect ratio) on dynamic response. Harmonic steady‐state as well as earthquake‐induced accelerations, displacements and shear strains in the dam are studied and compared with those obtained from 3‐Dimensional analyses for other canyon geometries, as well as from 2‐Dimensional (2‐D) analyses of the dam mid‐section. It is shown that such 2‐D analyses may provide significantly lower values of near‐crest accelerations, but slightly higher values of shear strains and stresses than the 3‐D analyses. The proposed method of analysis is at least three orders of magnitude less expensive than other presently availab