So - you're suggesting California breaks away, but Oregon doesn't, and isn't coerced into joining California?
I'm not saying I disagree, I just want to clarify what you are positing.
wolf_brother
I suspect that would be the case. Don't know enough about Oregon but it was pretty much all northern settled I think? Also no gold so no taxes on this by Washington. Also it's been American pretty much from the start while California was conquored from Mexico, has a Mexican element to the population and much of the recent immigrants, from America or elsewhere, are there for the gold and have little reason to be loyal to a distant Washington. Also it may consider itself big enough to stand on its own.
I don't think any of those would apply for Oregon. hence the reasons California has to seceded don't seem to apply. Also, once California has gone Oregon and the neighbouring Washington territory were the only option for the US to maintain a Pacific coast. As such I would expect they would seek to secure their grip on it. [Both possibly more troops and measures to make the population happier with their stance].
As such, unless someone attacks it and I don't think either California or Britain, the only neighbours in reach, have any reason to, I think it's unlikely Oregon would seek to fly the coup. [Unless the US response was particularly heavy handed possibly].
The only alternatives might be if the US, possibly lashing out in fear/anger/paranoia clashes with Britain or possibly California, fearing that the US will use Oregon as a staging ground for an attack to reclaim it launches what they see as a pre-emptive strike to occupy it first. You suggested that California would just declare independence and not make any hostile move, which is probably its best bet. [Even if Washington wants to do something after resolving a longer and more bitter war with the south, there might not be the appetite for a war at such a long distance. Also if California can use the time and the peace in the west to get international recognition and establish trading links with other powers that gives it a lot more status].
Furthermore war is expensive and Oregon is a long way from the goldfields. It might struggle to organise any sort of army for an invasion and especially to maintain it against any opposition. Also this means their less likely to get international recognition from the other powers, as they may be considered as destabilising and aggressive.
Anyway, hope this explains my thoughts on the issue.
Steve