Assuming the check is more than a couple hundred bucks, hire an attorney for $100 to $200 to send a demand letter for the paycheck plus your attorney costs to date. (Don't let the attorney do a lot of 'research' make it clear that initially you just want a demand letter. This establishes that the expense goes up the longer they delay. Or, file a small claims action.
Any idea how I might go about finding the attorney? The websites "california employment attorney" turn off look oddly spammy. Also what kind of things would you look for in picking an attorney? I am printing out forms for small claims now.
IMO for purposes of a demand letter on a small matter like this you could almost pick an attorney at random. Call a couple of solo lawyers who have small ads the yellow pages, explain what you want, ask for a quote for the initial demand letter. Also, instruct them to take NO further billable action after sending the letter w/o your express permission (to avoid them racking up another hour's fee to "review the reply" if your former employer sends them a reply). If they get a reply instead of a check, they should simply forward it to you. At THAT point contact your state labor board.