Say I harvest crop as a hobby on my land, and it's less than an acre. What's the tax on the crop income? In California.
If it's truly hobby, then income goes on line 21 of your form 1040 (miscellaneous income), and expenses go to your Schedule A line 23 (miscellaneous deductions) subject to the 2% AGI threshold. You cannot deduct more expenses than you have income (i.e.: You can't deduct hobby losses).
I'd suggest talking to a CA-licensed CPA or EA practicing in California, and familiar with this field.