California Code, Civil Code - CIV § 8834

(a) At least five days before giving the stop work notice, the contractor shall post notice of intent to give a stop work notice.  The notice shall comply with the requirements of Chapter 2 (commencing with Section 8100) of Title 1.  In addition to posting the notice pursuant to Section 8114, the notice shall also be posted at the main office of the site, if one exists.

(b) At the same time the contractor gives the stop work notice, the contractor shall give a copy of the stop work notice to all subcontractors with whom the contractor has a direct contractual relationship on the work of improvement.