A mathematical closed-form solution is presented for steady-state lateral response of earth and rockfill dams in canyons subjected to asynchronous excitation consisting of SH waves incident at an arbitrary angle. The dam is idealized with a 2-dimensional shear beam model and the canyon is considered rectangular in shape and consisting of elastic rock. An extensive series of parametric studies is undertaken to investigate the influence of the main parameters on the steady-state response by considering the effects of the dam-canyon interaction. In particular the study focuses on the effects of: (a) the angle of incidence, (b) the impedance ratio, and (c) the canyon narrowness. The solution is extended for a transient arbitrary excitation consisting of inclined SH waves for use in equivalent linear seismic analysis. (Abstract shortened with permission of author.)