This early June morning is Boyd Shepler’s birthday, No. 66, and he is spending it in a classic California way: a few hours of skiing in a snowflake-filled morning, then a round of golf in the dry afternoon sun. The snow here in the Sierra Nevada is epic, packed into a base that is more than double the historic average for early summer. Here on Mammoth Mountain, the ski lifts will be running into August. At lower altitudes, a spring of atmospheric rivers and hard rain has filled the state’s once-languishing reservoirs.