If I’m in another state, will I have to file for custody in from the state where I came from?

Both Oregon and California have adopted the Uniform Child Custody Jurisdiction Enforcement Act (the UCCJEA). Under the Act, the state where the child last lived for six months has jurisdiction to detemine child custody, parenting time and support. Once a court in that state has determined custody, that court retains jurisdiction to modify the original judgment unless that court decides to grant a motion to change jurisdiction to another state because the custodial parent and the child have lived in another state for a fairly long period of time. In addition, the court where the child currently resides can exercise emergency jurisdiction to protect the child from bad things, but the court that is being asked to exercise emergency jurisdiction would have to consult with the court that made the original custody determination. If you got sole custody under an order from a California Court and then moved to Oregon, and if the child has been in Oregon for a significant period of time, you can bring a motion in the California court to transfer jurisdiction to the Oregon county where you live. The motion would not automatically be granted but the court would evaluate the factors affecting the child's welfare. The court would also have to consult with the Oregon court to which you are asking for jurisdiction to be transferred.