"This bill would state that it is the policy of the state that eligible renewable energy resources and zero-carbon resources supply 100% of retail sales of electricity to California end-use customers and 100% of electricity procured to serve all state agencies by December 31, 2045."
Source: https://leginfo.legislature.ca.gov/faces/billTextClient.xhtm...
From this I take they don't plan to necessarily eliminate all carbon emitting energy sources but rather just the ones used to produce electricity. This would make the goal a little more achievable but also makes it a moving target. As different industries move from burning carbon based fuel to electricity the demand also increases which will still affect the balance between clean and dirty energy.
There are plans to ban ICE engines and other fuel burning applications so the demand for electricity will see a sharp rise. It's more that achievable to be 100% green in 2045 assuming the energy consumption trend of the past. But the future will probably see that trend go from relatively linear to something exponential for at least a few decades until the switch is done. Covering that difference will be the real challenge.
As always, devil's in the details. In the meantime, the headline looks impressive, which is frankly all these critters care about.