But, since facts and figures are key, if we assume the proportion of naturalized Mexicans naturalized in California in 2011 (39% of the total) holds true for previous years, and estimate that Mexican naturalizations since 1970 were at the same average rate as between 2002 and 2010, minus the outlier year of 2008 (almost certainly an overestimate), then there were about 1.37 million Mexicans naturalized in California from 1970 to 2010. Assuming 20% died, moved out of California, are not registered voters, or are too young to vote (almost certainly an underestimate), and 60% of the rest turned out (almost certainly an overestimate), that gets us to 660,000 votes - 250,000 still unaccounted for.
First of all about 20% of Hispanics in California are not Mexican. So that 250,000 unaccounted for shrinks considerably to about 75,000 assuming the naturalization rates are the same for the rest. http://www.census.gov/prod/cen2010/briefs/c2010br-04.pdf
Then we have to ask whether naturalization of Mexicans in California is only 39% of the total when averaged from 1970-2010. It is probably higher. Like I said, recently a greater proportion of Mexican immigration has headed to other places than California. Back in the 1980s and 1990s it was going in higher proportions to California. Also the 20% figure who have either moved or died is a little high. You have to remember that most immigrants are young and so the vast majority of immigrants from even the 1970s will still be alive. Also it's really the 1980s and 1990s where we saw a great increase in immigration. And averaged over 1970-2010, I really have to question whether there will be a net migration of immigrants from California to other states. Maybe native whites and blacks might be moving from California, I highly doubt that is the case with Hispanics or even Asians for that matter. And as for being too young to vote, if you come through legal channels, it can take up to 5-15 years to get naturalized. Many who came as kids would be eligible to vote, or at least within a few years of naturalization, in most cases. And immigration rates among the young are not that high iirc (double check me on this point though). Most immigrants tend to be from 20-40 years old. The young and definitely the old are underrepresented.