Traditionally, calls to split California in two have called for a north-south split, generally putting the SF Bay Area and Sacramento in the north, and LA in, well, Southern California along with its neighbors. (Though the proposed state of Jefferson would start roughly at Redding.)
Politically, though, it’s another matter altogether. It can be seen in the red-blue maps after statewide elections, and it can be seen in this map from the Sacramento Bee of how California’s representatives voted on the health-care reform bill.
