California’s high country is a delight in summer, a cool respite from the heat of the state’s lower elevations. That’s especially true in the Sierra Nevada, where a corridor of shade transports vacationers from Fresno to Yosemite National Park under a dense canopy of cedar trees, firs and pines. But after five years of drought and insect infestation, more than 66 million trees have died across the state, many in the eastern Sierra. In tree-ringed communities such as Bass Lake and Shaver Lake, up to 80 percent of the pines and other conifers have died.