91931 leans Republican by roughly 28 points: about 36% of voters vote Democratic and 64% Republican.
About 43% of adults in 91931 typically vote, below the U.S. average of about 62%. Among adults in 91931, ~15% vote Democratic, ~28% Republican, and ~57% don't vote. The map below shows estimated turnout by block group.
How 91931 compares
Among zip codes within 15 miles, 91931 leans more Republican than 1 of 5 neighbors.
91931 runs about 49 points more Republican than California as a whole. California leans Democratic overall, while 91931 is one of the few Republican-leaning pockets.
Why 91931 leans the way it does
This analysis examined 14,881 data points per zip code to find what predicts political lean and turnout. The items below are a few correlations that stood out for 91931, not a ranked or complete list of what matters most.
Rural areas vote Republican. About 1% of residents in 91931 live in densely developed areas, about 57 points below the California average of 58%. 91931 runs against the grain of California, a Republican-leaning pocket in a Democratic-leaning state.
Paved land cover and Republican lean
Places with little paved surface tend to lean Republican; 91931, CA sits in the bottom tenth nationally on this measure. Paved ground does not change how people vote; it mostly reflects how urban and built-up a place is.
Why turnout in 91931 looks the way it does
Crowded housing lines up with lower turnout. About 15% of homes in 91931 have more than one occupant per room, above 98% of zip codes. Strong routine healthcare access lines up with higher turnout, and 91931 sits in the top quarter on routine-care measures. Learn more about the findings and methodology on the political spectrum map.
Nearby Zip Codes
Zip Codes with Similar Populations
Sources and methodology
Precinct-level voting records used to fit the model come from California Secretary of State, Elections, distributed by the Voting and Election Science Team. Demographic inputs come from the U.S. Census Bureau (ACS 5-year estimates and the 2020 Decennial Census). Health and environmental inputs come from the CDC (PLACES and the Environmental Justice Index). Land cover comes from the USGS and EPA. Election-day and lead-up weather come from PRISM 4km daily grids and the NOAA Global Historical Climatology Network. Mail-voting and election-administration patterns come from the MIT Election Lab's Survey of the Performance of American Elections. Block-group crime detail comes from CrimeGrade. Internet data and modeling support provided by ISPreports.org.
Modeling and analysis by the BestNeighborhood data science team. Full methodology and findings: political spectrum map.
Methodology reviewed by the BestNeighborhood data team. Last updated May 2026.