California Code, Penal Code - PEN § 32311

(a) Except as provided in Article 2 (commencing with Section 32400) of this chapter and in Chapter 1 (commencing with Section 17700) of Division 2 of Title 2, commencing January 1, 2014, any person in this state who knowingly manufactures or causes to be manufactured, imports into the state, keeps for sale, or offers or exposes for sale, or who gives, lends, buys, or receives any large capacity magazine conversion kit is punishable by a fine of not more than one thousand dollars ($1,000) or imprisonment in a county jail not to exceed six months, or by both that fine and imprisonment. This section does not apply to a fully assembled large-capacity magazine, which is governed by Section 32310.

(b) For purposes of this section, a “large capacity magazine conversion kit” is a device or combination of parts of a fully functioning large-capacity magazine, including, but not limited to, the body, spring, follower, and floor plate or end plate, capable of converting an ammunition feeding device into a large-capacity magazine.