California Code, Insurance Code - INS § 9080.3

(a) In excess of 10 percent of its capital and surplus as shown in its last statement on file with the commissioner, on any one risk, or in excess of 20 percent of its capital and surplus as shown in its last statement on file with the commissioner in any one city block within an incorporated city without immediately reinsuring the excess over those amounts.

(b) On business property within any incorporated city.