what part of cali. do you live in?
i live in bakersfield and i get crawdads all the time
a trap is best or some times you can walk around in shallow water just after dark with a spot light and get them by hand.

or find a canal or river and set a chunk of chicken liver on the bank half under water or like a inch under the water then sit right next to it and wait every few min. use your flashlight to check on it.
the craw dads will come up ad try to steal it so just scoop them up when you see them or get a net if you dont want to use your hands