I am scheduled to return from mat leave in March and all indications point to my job being eliminated. They hired someone with a different title, but with my responsibilities. They eliminated a manager, 5 hours on her first day back from maternity leave.

What rights do I have in California?

You have no greater or less job security than if you had not taken leave. You can't be let go because you took maternity leave but you can be let go in spite of it.