Hi and welcome to JA. I am Ray and will be the expert helping you today.
If you want legal access here you would need to claim a prescriptive easement
.If you have used this road for at least five years you would have a valid claim here in California.
Here is reference to the requirements under California law.
In California this is the acquisition of an easement by adverse possession or squatters rights
California law allows that an easement is an interest in the land of a neighbor
or owner that allows you the owner of the easement to a limited use or enjoyment of the other’s land. A prescriptive easement is an easement that is earned by regular recurrent use you would sue here for quiet title to seek court ordered easement.This appears to fit your facts here.
You can keep using it here if you want and file suit if they challenge you here.
I appreciate the chance to help you today.Please let me know if you have more follow up.