We all know California, never a lily-white state to start with, has rapidly diversified over the last generation.  But California's White vote is far from monolithic.  It's not easy task to figure out what percent of the White vote Obama got in each county in the state, but I was inspired to try my best after the New York Times map of places where Obama got under 20% of that demographic (http://graphics8.nytimes.com/...).

My methodology was as follows:
1) Use exit polls to approximate the Black, Asian, and Hispanic vote for Obama vs Romney.  Due to the more heavily Vietnamese Asian population in L.A. and Orange Counties, I gave Obama only 70% of L.A.'s Asian vote and 65% of Orange County's.  Those are approximations, and mean that my numbers could be off, but I believe the true percentage is closer to those numbers than his 79% statewide.  Otherwise, I avoided changing the numbers.  I know Obama did better than 73% with Hispanics in some almost 100% Hispanic Central Valley towns but figured the range was close enough to 73% that it wouldn't matter.  I gave Obama 80% of the Native American vote, which wasn't part of the exit poll.

2) Use the Census to approximate turnout by race/ethnicity.  I adjusted all numbers downward (surprise, people lie and say they voted) to match actual turnout, which is an easy number to get using 2012 population estimates and actual vote totals.

3) Approximate Hispanic turnout in various counties (it's far lower among migrant workers in the Central Valley than in San Ysidro, Los Angeles, east San Jose, or Salinas, unsurprisingly) by looking at turnout in heavily Hispanic towns.  Hispanic turnout (as % of population, not VAP or CVAP) ranged from 10% in Kern County to 25% in Santa Barbara County.

4) Adjust for prisons (which boost minority population, especially in Kings, Lassen, and Del Norte Counties) by assuming demographically similar counties (Tulare, Plumas, and Humboldt, respectively) had similar voting populations.

I hope that all makes sense.  Even with that, there is some guesswork that must be done.  I'd hope my numbers are within three percent of the actual percentage, but in truth the margin of error may be up to five.  

I've drawn up a map.

Totals range from 90% (San Francisco) to 17% (Tulare and Colusa).  I'm going to go region by region, south to north.

Southern California:
San Diego (voters approximately 66% White, 19% Hispanic, 8% Asian, 7% Black): Whites 41% Obama.
San Diego's urban core gives it a relatively high percent of White Democrats.  I'm sure the numbers in the suburbs are far lower.

Imperial: 76H/18W/5B, Whites 29% Obama.  This is the only county in the state that is majority Hispanic if you look at the voters rather than the population.  As with much of Southern California, racial polarization looks more like Arizona than NorCal.

Riverside: 54W/31H/9B, Whites 28% Obama.  Riverside is (surprisingly and perhaps inaccurately) even worse than Imperial for White Democrats, by my calculations.  And that's even with Palm Springs helping to boost the numbers.

San Bernardino: 46W/36H/13B, Whites 24% Obama.
San Bernardino's numbers are about the same as Georgia or South Carolina.  It's Riverside County without Palm Springs.  However, I can't help but feel these numbers are a bit low.  Perhaps Hispanic turnout is lower than I thought it was.

Orange: 65W/19H/13A, Whites 33% Obama.
While there is much talk about Orange County getting bluer, you can see here why it's tough.  Almost 2/3 of the voters are White, and there are also some conservative Vietnamese votes.  

Los Angeles: 43W/33H/13B/10A, Whites 63% Obama.
Another one of the state's few majority-minority electorates, but the Whites are unsurprisingly pretty liberal too.

Ventura: 66W/25H/5A, Whites 42% Obama.
Ventura's numbers are quite a bit higher than other SoCal counties.  I'm not sure why that is, but it's high enough that I can't attribute it to my estimates being off.

Central Coast:

Santa Barbara: 64W/29H, Whites 50% Obama.
It's possibly I over-estimated Hispanic turnout here; my gut tells me a majority of the county's White voters went blue.  Interestingly, the map of White voters mirrors a 50-50 D/R race in the state almost perfectly.

San Luis Obispo: 82W/12H, Whites 45% Obama.
Obama managed to win this heavily White county thanks to the college town of San Luis Obispo.  

Monterey: 55W/33H/6B/5A, Whites 62% Obama.
Steinbeck Country votes like the Bay Area.

San Benito: 60W/35H, Whites 51% Obama.
It surprised me, but rural San Benito's Whites are pretty liberal.

Santa Cruz: 79W/14H, Whites 80% Obama.
The results from this hippie haven should surprise nobody.  It trails only SF and Alameda.

Central Valley:

Tulare: 57W/36H, Whites 17% Obama.
Kings: 62W/31H, Whites 22% Obama.
Tulare County is a lot like Texas, but with a few more Mexicans and far fewer Blacks.  Its twin, Kings County, is similar in almost every respect.  I chalk up the 5% difference to my margin of error.

Kern: 66W/19H/10B, Whites 22% Obama.
For all the talk about Oklahoma, I think Kern County's Whites may be even more conservative.

Fresno: 58W/25H/10B/7A, Whites 30% Obama.
My guess is that we can chalk up the 8% difference between Kern and Fresno to the oil industry.

Madera: 63W/28H/7B, Whites 20% Obama.
Merced: 48W/41H/6B, Whites 30% Obama.

These two counties are both smaller.  Merced is another majority-minority electorate, but its Whites are more liberal too.  Possibly helped by the college.

Stanislaus: 66W/25H, Whites 38% Obama.
San Joaquin: 54W/24H/12B/10A, Whites 37% Obama.
San Joaquin's light blueness compared to Stanislaus's light redness can be chalked up to diversity, not the preferences of its White voters, who are more liberal in either county than they are anywhere else in the valley.

Inyo: 76W/12H/12NA, Whites 33% Obama.
Mono: 83W/14H, Whites 50% Obama.
Alpine: 73W/20NA/5H, Whites 56% Obama.
Guess which one doesn't have ski resorts and second homes.

Tuolomne: 89W/6H, Whites 37% Obama
Mariposa: 90W/6H, Whites 36% Obama
Calaveras: 90W/6H, Whites 37% Obama
Amador: 87W/8H, Whites 34% Obama

These four are almost as identical as they come.

Siskiyou: 88W/5H, Whites 37% Obama
Lassen: 91W/5H, Whites 25% Obama
Modoc: 86W/7H/5NA, Whites 21% Obama
Plumas: 92W, Whites 38% Obama
Sierra: 95W, Whites 36% Obama
Nevada: 94W, Whites 48% Obama

Tahoe helps make Nevada bluer, and Modoc and Lassen are basically Southwestern Idaho.  The others are the same as mountain counties all over the state's eastern tier.

Sacramento Area:

El Dorado: 91W/5H, Whites 37% Obama
Placer: 87W/6H, Whites 35% Obama

Suburbs and skiiers.

Sacramento: 62W/13B/13H/10A, Whites 46% Obama
Half Sacramento itself, with liberal Whites, and half suburban, which similar votes to Placer.

Bay Area:
San Francisco: 64W/22A/7H/6B, Whites 90% Obama
90% is a crazy number.  That's all I have to say on the matter.

Alameda: 49W/20A/17B/13H, Whites 81% Obama.
The wealthier 680 corridor stops these numbers from being similar to SF's.

Contra Costa: 63W/13H/12B/11A, Whites 60% Obama.
In the Bay Area, this is conservative.

Santa Clara: 54W/25A/16H, Whites 67% Obama.
Tech stops this from being the same as Contra Costa.

San Mateo: 61W/19A/14H, Whites 71% Obama.
A tad poorer than Santa Clara, and also doesn't have Gilroy or Morgan Hill.

Marin: 86W/6H, Whites 76% Obama.
Famous for rich liberal Whites.  The fame is deserved.

Sonoma: 81W/12H, Whites 73% Obama.
Higher than I expected.

Solano: 56W/19B/14H/10A, Whites 50% Obama.
Fairfield and Vacaville feel like Texas if you grew up in the Bay.

North Coast:
Napa: 74W/17H/5A, Whites 60% Obama.
It's not really on the coast, but it had to go somewhere.

Mendocino: 80W/12H/6NA, Whites 69% Obama
Lake: 85W/10H, Whites 56% Obama
Humboldt: 86W/6NA/5H, Whites 63% Obama
Some of the most liberal rural Whites in the country live here

Del Norte: 85W/6H/6NA, Whites 39% Obama
I'm the least confident about these numbers since I had to adjust for the prison.

Trinity: 91W, Whites 47% Obama
I know nothing about this county except it barely has any people.

Sacramento Valley:

Yolo: 68W/18H, Whites 63% Obama
Yeah, yeah, we have a county called Yolo.  The college keeps it blue.

Colusa: 62W/33H, Whites 17% Obama
Glenn: 77W/18H, Whites 25% Obama
Tehama: 87W/10H, Whites 30% Obama
Sutter: 70W/14H/10A, Whites 24% Obama
Yuba: 75W/16H/5B, Whites 28% Obama
Butte: 86W/8H, Whites 44% Obama
Shasta: 91W, Whites 31% Obama

Colusa's numbers seem a bit low.  This area is very conservative, except the college town of Chico.  Even Redding, a real population center, is barely above 31%.

So there you have it.  I'm hoping to do this for more states if I have the time.

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