They posted the entire poll and the crosstabs definitely look solid:
Whites: Hillary 46-42 (remember, there are more affluent whites in California and some of them might break her way. There is also a decent-sized Jewish population in CA and she's crushed him 2-1 with the Jewish vote)
Hispanics: Hillary 51-39 (this makes sense if younger Hispanics are breaking away from her while older Hispanics vote for her)
African-Americans: Hillary 71-9 (I think this is a little optimistic for her and she'll carry 3/4 of the African-American vote instead of an Alabama-type margin).
Asians: Hillary 56-33 (She's had a better organization with the Asian-American community here for a far longer period than Sanders. Younger Asians might be breaking for him but their parents and grandparents are almost certainly going for her, especially the grandparents)
18-29: Sanders 61-30 (Now you're thinking, shouldn't he be winning the California youth vote by more? Remember minorities comprise a majority of the youth vote in CA so his margins might not be as drastic as in other states where he won 75-80%)
30-44: Hillary 48-38 (Once again, minorities make up about half of this age group in California as well so it makes sense that she's winning narrowly here).
45-64: Hillary 57-36 (Very much in line with other states)
65+: Hillary 63-22 (Very much in line with other states)
Now the bit of good news for Sanders supporters:
They undersampled independents. 90% of the electorate in this poll is registered Dems. In 2008, 79% of the electorate were registered Dems while 21% were not. Adjust that to 80-20 and you get Clinton 48, Sanders 42, which is almost exactly what Field showed the last time
http://www.hoover.org/sites/default/files/golden_state_poll_may_2016_results_tables_final.pdf#overlay-context=press-releases/hoover-institution-golden-state-poll-californians-have-their-eye-water-and-jobs-wary
