San Bernardino is probably where the bulk of the reloads are coming from.
The bases that can handle multiple VLAT (Very Large Air Tanker) in CA are Mclellan up in Sac (CalFire) and San Bernardino (USFS). Riverside may be able to handle VLAT’s but not sure as they are CalFire and I’m a Fed.
Either one of those is a very short turnaround in comparison to fires inland.
You also have quite a number of CalFire tanker bases that can only handle LAT’s and smaller, then you have Type 1 Helitanker bases ram by Fed and state as well as SDGE, Edison, and PG&E throughput the state.
There are challenges to all this though. Retardant has to be made in a mixer, multiple sorties stacking up, availability of lead planes, Air Attack planes (like the offensive coordinator in the sky), wind, time of day, and even drone activity (a helicopter struck a civ drone the other day on the fire).