Environmental advocates have all but given up on their long-cherished goal of a federally-mandated cap-and-trade program to rein in carbon emissions, given the present state of gridlock on Capitol Hill. But amid protracted hemming and hawing over how such a system would stack up against carbon taxes or other broad incentives to reduce emissions, the state of California has stepped in where Washington policymakers fear to tread. California formed its own state-mandated carbon market in…