Cal. PCC § 20121

Whenever the estimated cost of construction of any wharf, chute, or other shipping facility, or of any hospital, almshouse, courthouse, jail, historical museum, aquarium, county free library building, branch library building, art gallery, art institute, exposition building, stadium, coliseum, sports arena or sports pavilion or other building for holding sports events, athletic contests, contests of skill, exhibitions, spectacles and other public meetings, or other public building or the cost of any painting, or repairs thereto exceeds the sum of four thousand dollars ($4,000), inclusive of the estimated costs of materials or supplies to be furnished pursuant to Section 20131, the work shall be done by contract. Any such contract not let pursuant to this article is void.