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.
In the 1850s and 1860s, what is now the Los Angeles area was more Democratic than the San Francisco area because southern California was dominated by Mexican American landowners who were sympathetic to the planter class of the American South while San Francisco was populated by Forty-Niners and their descendants who leaned toward the Republican Party and were responsible for California's admission to the Union as a free state.
As an example, in the 1860 Presidential election, Lincoln won California due to the split in the Democratic vote and his strength in the Bay Area while Los Angeles County voted for Breckenridge.
https://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/California_Presidential_Election_Results_1860.png/640px-California_Presidential_Election_Results_1860.png
