Registered domestic partnerships in California are the functional equivalent, as far as the law goes, of marriages without the title of marriage. RDPs retain all community property rights, all parental rights and responsibilities, and every other benefit and detriment of marriage. As far as California law is concerned, those unions are equal to marriage.
The difference comes with the federal government, especially if an RDP dissolves: there are massive federal tax consequences for RDPs that dissolve. For example, if an RDP is dissolved, one can’t deduct support payments from federal taxes. Another difference is that property division is also federally taxable. Neither of these would be the case in a standard divorce.