There were 8 counties that were more responsible for Proposition 8 passing than any others, based on sheer numbers coupled with sizable win margins. (There were many smaller eastern state counties that had larger margins of victory, but were relatively small in numbers. I'm ignoring those because they're essentially nickles and dimes.) Those 8 counties are (ranked by yes-minus-no net sheer number):
San Bernardino -- 67.1 YES (a yes-minus-no net of 162,198)
Orange -- 57.5% YES (net of 131,691)
Riverside -- 64.3% YES (net of 118,241)
Kern -- 75.3% YES (net of 97,957)
San Diego --54.0% YES (net of 76,608)
Fresno -- 68.8% YES (net of 71,810)
San Joaquin -- 65.5% YES (net of 51,361)
Stanislaus -- 68.1% YES (net of 44,601)
In looking at those eight counties we see a clear pattern: they are all conservative counties with long traditions of voting for Republicans (from wikipedia).
San Bernardino County is a predominantly Republican county, with Barack Obama in 2008 and Bill Clinton in 1996 being the last Democrats to win a plurality in the county.
Riverside is a strongly Republican county in Presidential and congressional elections. The last Democrat to have won the county was Barack Obama in 2008. Before him the last democrat to win the county was Bill Clinton. In the House of Representatives, Riverside is mostly in California's 45th congressional district, with parts in the 41st, 44th, and 49th districts. All four districts are held by Republicans, the 41st by Jerry Lewis, the 44th by Ken Calvert, the 45th by Mary Bono, and the 49th by Darrell Issa.
Kern is a strongly Republican county in Presidential and congressional elections. The last Democratic candidate for President to win a majority in the county was Lyndon Johnson in 1964.
San Diego County is a slightly Republican county. The city of San Diego itself, however, is more Democratic than the county's average (though fairly moderate compared to the national and state average) and has voted for Democrats Clinton, Gore, and Kerry in the last four presidential elections respectively.
Fresno County today is a strongly Republican county, voting for President George W. Bush by over 55% of the vote in 2004, although it remains closer in Senatorial races.
San Joaquin is a Republican-leaning county in Presidential and Congressional elections. The last Democrat to win a majority in the county before 2008 was Lyndon Johnson in 1964, although Bill Clinton won pluralities in the county in 1992 and 1996. However, in 2008, Democrat Barack Obama won 54% of the county's vote.
Stanislaus is a strongly Republican county in Presidential and congressional elections. The last Democrat to win a majority in the county was Jimmy Carter in 1976.
In fact, none of these counties are politically Democratic where you might expect to find large African-American populations. Only one of these eight counties has a significant African-American population: San Benardino (9.1%). Most of those live in the city of San Bernardino accounting for more than 18% of that city's population. However, they are largely low-income and mostly segregated to the western part of the city in a housing project.
Five of the remaining seven have roughly average African-American populations relative to California's overall 6.2%: San Joaquin (6.7%), Riverside (6.2%), Kern (6.0%), Fresno (5.3%), and San Diego (5.0%).
Two have relatively small African-American populations: Stanislaus (2.6%) and Orange (1.7%).
I don't think Proposition 8 passing has anything to do with African-Americans. I think it has everything to do with Republicans (decidedly NOT African-Americans) and Mormons (also decidedly NOT African-Americans).
Orange, San Diego and San Benardino counties have the largest Mormon populations of any county in California other than LA County. Orange County has 115 LDS congregations, San Diego has 112, and San Bernardino (which was founded by Mormons in 1852) has 95. Outside of Utah and Idaho, that represents the 4th, 5th and 6th largest Mormon communities in the entire country (following only Maricopa AZ, Los Angeles CA, and Clark NV).
http://www.adherents.com/...
Not only did the Utah-based Mormon church bankroll Proposition 8, the large contingent of California Mormons, disproportionatelly represented in those three counties, voted for it in large numbers.