"Interest is the only income so no CA source income"

If interest was earned by a CA trust, that IS California income.

No OR return for the trust, its California trust, unless it had something generating income from the state of Oregon (like an OR rental property), you wouldnt need an OR trust return.

Your OR beneficiary will get the 541 k-1 for his share of the trust income You may need to mark a check box on the 541 that you have a non-resident bene (It might mark it for you automatically when you enter an out of state address for the beneficiary, I cant remember).

And he may very well have a CA filing requirement, if his worldwide gross income is over $21,561  CA will compute the tax on all income and then multiply it by the % of CA income vs all other income, of course he would get credit for taxes paid to another state, since the CA income would be taxed by OR as well as CA.