I'm not familiar with OR law, however I am with CA vehicle code and dmv processes.
If the car is reg'd in OR (either with a one way trip permit or otherwise), you're legal in CA until the permit expires or otherwise becomes invalid (i.e. no longer traveling from point a to point b). Interestingly, the OR DMV website says their permit is for trips "within Oregon", however not sure how legal that is. You'll need to verify.
If you want to be covered, you can apply for a CA REG 402 or "TOP", which allows for "one continuous trip", including from placed outside of CA.
https://www.dmv.ca.gov/portal/handbo...rmit-reg-402t/
https://www.dmv.ca.gov/portal/vehicl...ating-permits/
BTW - are you positive you can register this car in CA once you get there? I.e., it'll smog, etg.