what are the laws on this in Ca

All NFA rules apply as does the requirement to get a special permit from the DOJ to have a short-barrel/sawed-off chotgun.  This assumes you have a shotgun it will fit.

Short version is no way in hell.  Shotgun has to be 26 inches overall or longer AND have a barrel length 18 inches or longer.  Was this a serious post??  How long have you been in this damn state??

Read on...from the PRK doj website...

12095. (a) If it finds that it does not endanger the public safety, the Department of Justice may issue permits initially valid for a period of one year, and renewable annually thereafter, for the manufacture, possession, transportation, or sale of short-barreled shotguns or short-barreled rifles upon a showing that good cause exists for the issuance thereof to the applicant for the permit. No permit shall be issued to a person who is under 18 years of age.
(b) Good cause, for the purposes of this section, shall be limited to only the following:
(1) The permit is sought for the manufacture, possession, or use with blank cartridges, of a short-barreled rifle or short-barreled shotgun, solely as props for a motion picture, television, or video production or entertainment event.
(2) The permit is sought for the manufacture of, exposing for sale, keeping for sale, sale of, importation or lending of short-barreled rifles or short-barreled shotguns to the entities listed in paragraph (1) of subdivision (b) of Section 12020 by persons who are licensed as dealers or manufacturers under the provisions of Chapter 53 (commencing with Section 5801) of Title 26 of the United States Code, as amended, and the regulations issued pursuant thereto.

12001.5. Except as expressly provided in Section 12020, and solely in accordance with Section 12020, no person may manufacture, import into this state, keep for sale, offer for sale, give, lend, or possess any short-barreled shotgun or short-barreled rifle, as defined in Section 12020, and nothing else in this chapter shall be construed as authorizing the manufacture, importation into this state, keeping for sale, offering for sale, or giving, lending, or possession of any short-barreled shotgun or short-barreled rifle, as defined in Section 12020.

From Section 12020...(c)(1) As used in this section, a "short-barreled shotgun" means any of the following:
(A) A firearm which is designed or redesigned to fire a fixed shotgun shell and having a barrel or barrels of less than 18 inches in length.
(B) A firearm which has an overall length of less than 26 inches and which is designed or redesigned to fire a fixed shotgun shell.
(C) Any weapon made from a shotgun (whether by alteration, modification, or otherwise) if that weapon, as modified, has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length.
(D) Any device which may be readily restored to fire a fixed shotgun shell which, when so restored, is a device defined in subparagraphs (A) to (C) inclusive.

-hanko