Looking north from Blue Canyon near Shaver Lake, copper-colored forests blanket mountain slopes that stretch ridge after ridge to the horizon. The patches of fading green that dappled these hillsides last fall have merged into an unbroken cover of rust-needled pines.  At dusk, when the winds die down, an eerie stillness gives way to the muffled sound of munching as beetles chomp through one tree after another, thousands after thousands. This is the look — and the sound — of drought. Four consecutive winters with little to no snowpack, followed by four dry summers, have devastated California’s southern Sierra Nevada.