This legislation restricts what type of generation is used when buying that power. I understand it can be coal, but it must be a "clean" coal technology.
I read the legislation. It simply sets a benchmark for CO2 emissions. Any new plant cannot have CO2 emissions that exceed those that would occur from a new natural gas fired combined cycle plant.
Natural gas is CH4 (i.e., a bit of carbon and lots of hydrogen). Coal is essentially 100% carbon (excluding the 10% ash and a very wee bit of hydrogen). "Clean Coal" technology reduces emissions of other nasties such as sulphur and nitrogen oxides and mercury as well as pushes efficiency above 45% in combined cycle plants. But you are still burning pure carbon, so there is no way the CO2 emissions from a combined cycle coal fired plant can be less than the CO2 emissions from a combined cycle natural gas fired plant.
In other words, the bill bans new coal fired plants.
The loophole is the long-term financial contract clause. Utilities can simply sign power contracts for durations less than 3 years. That is the reason all three of California's investor-owned utilities supported the bill.