Fire regimes and forest structures were reconstructed over large landscapes at Grand Canyon National Park and Kaibab National Forest, totaling ~ 6,600 ha and ranging from ponderosa pine to spruce-fir and aspen forests (elevation range 2,200 to 2,800 m). Fire patterns changed from frequent surface fires (mean fire intervals 3.2 to 6.9 yr) at lower elevation to a complex mixture of surface fires and sporadic stand-replacing fires at higher elevation, strongly influenced by aspect. Climatic influences were most evident in very dry years, such as 1735, when synchronous fires burned across large areas. Grand Canyon landscapes ceased to burn in the late nineteenth century, but a few remote sites experienced occasional fires in the twentieth century. Modern forests thus include some ponderosa pine forests with minimal human-caused disruption, other pine and mixed conifer forests with extensive change associated with fire exclusion (increased density of young trees, increase in fire-susceptible species), and high-elevation aspen and conifer forests recovering from severe nineteenth-century fires. Landscape-scale information has set the context for small-scale experiments in forest restoration, testing four treatments: (1) fire-only, (2) fire + minimal thinning, (3) fire + thinning to restore forest structure, (4) and control. Finally, we used landscape information in vegetation simulation and fire behavior models to assess fire hazard changes between 1880 and 2040.