What if the mother told the father she was leaving the state with the child and she is now going back to retrieve her things and takes the child with can the father prevent her from leaving. She is going to California

Is there an existing court ordered custody order? If there was then he would have something that could be enforced.

No, he cnt prevent her without a court order in place. But he could possibly force the return of the child. What exactly is happening?

She is going to CA or they live in CA? If she is going to CA then the laws that matter are the laws in place where they live now.

And, as noted, it really depends on what court orders currently exist for custody and visitation.

If you are the father and believe she plans to move (or has moved), then you need to move quickly and file for custody and a temporary order restraining her from moving until custody can be established.

Father needs to proactively file asap. This happened to my daughters mother in law. She went back to Ohio to take her daughter to Georgia and was ordered to return her. Get an order in place before she returns.