What you're proposing is probably a state with less population than Wyoming. We don't need more states like that. In fact, we should be eliminating states like RI and WY, and combining those areas with other regions to form more populous states, so we don't have this problem where we have some states that have enormous populations and some with puny populations; they should be more equal.
Instead, if northern Californians don't want to be part of the same state as the Bay Area, maybe they should push instead to join Oregon.
Edit: Sorry, I thought this was a proposal along the lines of the State of Jefferson, to break off the very northern part of California, in wine country, north of the Bay Area.
Yeah, splitting the state in half around the mid-section does make sense; the state is too large, and the north and south halves are pretty different from each other. While they're at it, Las Vegas should probably join the southern half.