Right, so if you think of Californians as different and are prejudiced against them then it says more about you than them. It doesn't matter whether it's because of their ancestry or choice of location to live.
They're still not a race, but you're welcome to think whatever you want, even if it's inane. In regards to race being a construct, the consensus is there more so because nobody wants to rock that boat rather than because it's unquestionably true. Sadly, discussing taxonomical differences between various races and ethnicities often leads to talk of supremacy, so most people prefer to keep that can of worms closed, especially after what happened in the 20th century. Dawkins speaks on that matter at length and once explained why avoiding the discussion of race as a biological fact rather than a social construct is a mistake that sets science and medicine back. If differences in the genome were explored properly without the stigma of "racist research" hanging over the endeavour, many preventable diseases could be mitigated before they cause damage in ethnic groups that are particularly susceptible to them.
https://time.com/91081/what-science-says-about-race-and-genetics/
Sadly we can't have such nice things and the subject will always be a field of egg shells that must be danced around. Can't be helped, I suppose. The idea that humans who evolved under vastly different conditions are exactly the same, or that evolution got to a certain point and then suddenly stopped, is not just silly on the face of it - it's flat out wrong. Humans have adapted and continue to adapt to their surroundings, regardless of whether we think that's racist or not.