Exxon Mobil late Thursday flagged it might write down the value of its California assets by as much as $2.6 billion.The oil giant XOM, -0.87$2.4 billion and $2.6 billion in its upstream division mostly reflects idle upstream Santa Ynez Unit assets and associated facilities in California.“While the Corporation is progressing efforts to enable a restart of production, continuing challenges in the state regulatory environment have i ...