My grandfather has a few Gambel quail, which are very similar in behavior and size to the California quail. His birds are rather flightly and timid; however, they're more inclined to run than to fly up and hit their heads on the top of the pen. The birds seem to prefer having places to roost and perch, so it would be good to have places for them to do so that are large enough for their feet. Trimmed tree branches or wooden doweling rods greater than half an inch thick would be my recommendation. I would also recommend having places for them to hide when frightened as well, such as box-like shelter or something of the sort.
Overall, these aren't difficult birds to keep, and in spite of their relatively short laying season and occasional intolerance of people, they're really wonderful birds.
Best of luck!