I think probably a bad idea. DFG law makes it pretty clear that if you're catching fish for bait you need to catch it by hand, with a dip net, or using a trap. You can read about it at:

http://www.fgc.ca.gov/2006/06freshfishregbook.pdf

Look in the Bait Regulations Chapter. I seem to remember that it used to be legal to use umbrella nets but they don't make mention of that in there any more.