For the better refuges, you need a type A permit. You can buy a season pass for about $12, a two-day pass for about $25, and a one-day pass for about $15. (I'm a little off on the numbers, but close.) You probably will want the single or two-day passes. The singles are sold at the refuges in the morning. Two-days you need to get from a DFG office.
Here is a guide to public refuges, and the regulations:
http://www.dfg.ca.gov/docs/06-Waterfowl-Upland-Lands.pdf
There are A, B, and C refuges. A's have the fees I cited. B's have a season pass at about $40, and C's are free.
Kern is the southernmost refuge in the Central Valley. Drive about an hour and a half North, and you hit Mendota. That's a pretty good refuge (12,000 acres with a hunter capacity of 600.) Except for opening weekend, you can always get on there, and it shoots a lot of ducks. There are even more refuges farther North, and more and better ones above Sacramento.
There are plenty of places to duck hunt, and some very good ones. Kern is a hotspot for Cinnamon Teal, that's why I asked you in the first place if you wanted to go there in search of one.
Good luck.
Tom*