California Development - Property Tax Assessments pre-completion?

More of a modeling question. Assuming I buy a piece of dirt for $10MM and develop a project with an end-value of $50MM, during the development process, when budgeting for property taxes during the 36 months before C of O is issued, are my taxes going to be based on the $10MM initial purchase at whatever the millage rate is? At what point should a developer expect the assessor to reassess the site based on the new construction valuation? In California especially, where values are based on sales value with Prop 13.