No place to build an upstream dam but there are two downstream facilities that do the same thing. One is the Thermalito Afterbay and the other is Don Pedro Dam. Oroville serves as the upstream capacitor for the lower dams.
I'm not sure where the connection to send water to LA is.
The Feather River channel through Oroville is apparently well below a 100K cfs release.
The most recent significant event had a ~250k cfs inflow to Oroville. If they want to store max. water in Oroville, they need to have, perhaps, multiple structures upstream to keep the inflow within the outflow capability over a day or two.
Not sure what happens during Spring melt.
There are several upstream dams and they are at 100% capacity.