I'll bet the other 1/3 are anchor babies.
how abut 1/2 or more for California, where 50% of the 33 million population are immigrants or children on immigrants, which surely cannot be legal, since the government hasn't allowed 15 million to enter legally in the last two generations and of these, The 2000 Census found that 36.9 percent of California's foreign-born population had arrived in the state since 1990.
http://www.fairus.org/Research/Research.cfm?ID=1408&c=9