I'd like to draw you a picture.
Sometimes in California, everything beyond the fog is written off as "too Republican" to be contested by Dems. I would like to refute this. Certainly, Republicans do well in the Sierra, where they enjoy a large registration advantage, but the real picture is more complex. There are opportunities in them thar hills.
As you can see, eastern California is not a crimson wasteland. Obama did well for himself across the region (and, just across the border, he won Reno, too). In CA-4, Charlie Brown did even better!
Placer County is a great example: in a county that is 50% Republican, Obama did quite well from Auburn up. That pattern repeats itself elsewhere in the Sierra, creating 'pockets' of Dem sympathy in otherwise hostile territory.
I wanted to create this map before getting to the CA-3 and CA-25 posts for two reasons. First, as mentioned above, this is not an incontestable region. Second, I believe a sense of momentum is necessary to have any success in these and other Obama Eight districts. Building momentum requires starting from a base and working outward, and even in unfriendly terrain there are places from which momentum can be built.
Unfortunately, the Sierra is just the low-population rural area attached to several districts. 80% of CA-3's voters are in Sacramento County and most of the voters of CA-25 are all the way down in L.A. County. In close elections, though, marginal areas can't be neglected. Certainly not those that show promise...