You may want to look at
http://www.courts.ca.gov/17976.htm
This link will take you to the official court system in California. They do have a page of general information on Grandparents Visitation rights. Of course that is just general information and only an attorney can give you legal advice on your specific case.
Some questions you may want to ask your attorney: Does it matter which state you file your petition in? (it could be California since you live there, Arizona since the children live there or if the children lived in a different state prior to the adoption it maybe that state). How are you supposed to show to the court that you had a pre-existing relationship with the children?