Right about down the San Andreas fault. That could be the border.
No, that won't work. More complicated than that. The San Andreas cuts west into the Pacific just south of San Francisco. San Francisco would then be on the State of Jefferson side to the north. You probably mean the Hayward Fault, which goes north on the east side of SF. But it cuts Berkeley in half, so you still end up with a large portion of liberals on the Jefferson side. That's why I say you need to split the state into 3 to 6 sections, which are largely distinct from each other. An area surrounding SF east to Sacramento. Another area surrounding LA. The northernmost section of California to Jefferson. Central valley to Nevada. At the very least. The San Andreas doesn't split along political lines.