California Code, Streets and Highways Code - SHC § 1460

(a) Make an opening or excavation for any purpose in any county highway.

(b) Place, change or renew an encroachment.

(c) Place or display in, under or over any county highway any kind of advertising sign or device.  Any such sign or device placed or displayed contrary to the provisions of this section is a public nuisance and the road commissioner may immediately remove it.  The provisions of this section shall not prohibit the posting of any notice in the manner required by law or by the order of any court of this state.

(d) Plant, remove, cut, cut down, injure or destroy any tree, shrub, plant or flower growing within any county highway.

Any person who does any of the acts specified in this section, without the authority of such a permit, is guilty of a misdemeanor and is liable to the public agency for all expenses and damages caused thereby.