DENVER — Vast swaths of the ponderosa pine forests that blanket Colorado’s Front Range mountains could turn rust-colored and die over the next five years as pine beetles begin to spread aggressively, new federal forecasts show. Aerial surveys conducted by the U.S. Forest Service over the last year found evidence of rapidly spreading beetle infestations along the mountains and foothills that stretch from southern Larimer County to southern El Paso County, including the western flank of metro Denver. Already, pockets of dead trees are visible from Interstate 70 and U.S. 285. The rapid uptick in beetle-killed trees near the state’s largest cities and major highways prompted state leaders to form a task force this month to grapple with the outbreak. Gov. Jared Polis issued an executive order Dec. 15 and created the Mountain Pine Beetle Ponderosa Outbreak Task Force to address the growing wildfire threat and the beetles’ potential impact to watersheds, recreation and infrastructure.