Once upon a time Napa Valley was a place of pastoral legend. Blessed with the bucolic beauties of wooded knolls, forested slopes, springtime fields dappled with mustard flowers, summertime’s lush greenery, the valley aflame in reds and yellows come fall. The human presence was a smattering of vineyards and family-owned wineries, dairies, cattle ranches, walnut groves, plum-tree orchards. Toda...