Cal. Health & Safety Code § 41812

(a) The air pollution control officer of any district, upon authorization of the district board, may authorize, by permit, open outdoor fires for the purpose of disposing of agricultural wastes, or wood waste from trees, vines, bushes, or other wood debris free of nonwood materials, in a mechanized burner so that no air contaminant is discharged into the atmosphere for a period or periods aggregating more than 30 minutes in any eight-hour period that is either of the following:
1. (1) As dark or darker in shade as that designated as No. 1 on the Ringelmann Chart, as published by the former United States Bureau of Mines.
2. (2) So opaque that it obscures observer’s view to a degree equal to or greater than does smoke described in paragraph (1).
(b) In authorizing the operation of a mechanized burner, the air pollution control officer may make the permit subject to whatever conditions the officer determines are reasonably necessary to ensure conformance with the standards prescribed in this section.