Inside the CA 541 there is (will be) a grid for sourcing the CA source income (and the residency of fiduciaries and beneficiaries).  I'm assuming you're filing in CA because the trust has CA source income (e.g., owns rental properties)?

And if not already, be aware of the accumulation distribution rules in CA together with 'CA expat' rules.  There are also recent cases regarding residency of (contingent) beneficiaries, etc.  Link below is old and should be updated but it might give you some background info that might be helpful.

A shakeup in trust taxation: Kaestner and Paula Trust