what type of states politically/culturally would "Northern California" & "Southern California" be?

[Kamala's side hoe]

Culturally, again I think it would be similar to current NorCal/SoCal divides, but perhaps more pronounced. Which is to say, NorCal would feel even more like a northeastern state than it already does, and SoCal would be more Sun Belt-y than it already is.

I don't really think of NorCal as being culturally similar to any part of the Northeast- not least because California seems to define itself in opposition to the entire country east of the Rockies. Agree with you on the politics aspect.

[Kamala's side hoe]

If they split tomorrow? Both blue states anchored around San Francisco and Los Angeles with their own laundry lists of obstacles for Republicans. Population losses would be hitting NorCal much harder proportionally and the current problems in the tech industry wouldn't bode well for its economy, and while SoCal would have and maintain a larger population and a more diversified economy, its per capita personal income and income disparity might look worse. SoCal would inherit the oil and gas industry and Los Angeles' car culture, while NorCal would be freer to pursue an environmentalist agenda. SoCal's five UC and twelve CSU campuses, while prestigious, would struggle being disconnected from the rest of the university system. The North would inherit the Sacramento government, and the more interesting political developments would be in SoCal.

It would be interesting to see how the environmentalist movements in Los Angeles and San Diego would evolve in a hypothetical independent SoCal. I'm guessing the seat of the new state government would be based somewhere in Los Angeles proper?

[Kamala's side hoe]

It depends upon which part gets the Central Valley. The San Francisco- San Jose area votes much like Greater LA anyway. 

That actually makes me wonder if Greater Los Angeles was ever more D/less R than the Bay Area.

The answer often given for this question is that OC was strongly conservative due to post-WWII suburbanization as well as the presence of the Cold War-era defense industry. However, looking at past election results, it seems to go much deeper than this- IIRC, Orange County was already one of the most Republican counties in California by the 1920s (along with tiny Alpine County in the Sierras).

In 1884, in Los Angeles County (which at the time also included present-day Orange County), a total of 10,829 votes were cast. James Blaine won the county by eight points, making Los Angeles County two points more Republican than the state as a whole. In 1888, the first election after the beginning of the wave of immigration, the total vote in Los Angeles County was 25,264 votes, more than double what it had been just four years ago. While Cleveland improved on his previous performance statewide, in Los Angeles County this time Benjamin Harrison won by fifteen points, making the county thirteen points more Republican than the state as a whole. From a political perspective, greater Los Angeles was created in the late 1880s, and it was created by Republicans.

[Kamala's side hoe]

You'd also have to wonder how both domestic and foreign immigration to OTL California would differ in this scenario, and how they would affect NorCal and SoCal respectively.