In the Democratic horserace, Clinton leads Sanders among likely voters ages 45 and older (63 percent to 33 percent), self-identified Democrats (57 percent to 40 percent), women (54 percent to 41 percent), past Democratic primary voters (53 percent to 42 percent) and whites (51 percent to 46 percent).
Clinton also is ahead among those who have already voted, 58 percent to 41 percent.
Meanwhile, Sanders leads among first-time participants (72 percent to 28 percent), independents (68 percent to 26 percent), those younger than 45 (66 percent to 30 percent), men (54 percent to 43 percent) and Latinos (49 percent to 46 percent).
"As throughout the primary season, age is the story in this California tossup," says Lee Miringoff, director of the Marist College Institute for Public Opinion. "Sanders inspires younger or first-time voters, and Clinton relies upon those who are older or have participated in the past."
Geographically, Clinton is ahead in the Bay Area (56 percent to 42 percent) and Los Angeles County (54 percent to 40 percent), while Sanders has the advantage in the inland/valley areas (54 percent to 44 percent) and the coastal region (58 percent to 36 percent).