Q: Does a non-property owner have full use rights of an access road in Shasta County, CA?

A: The people staying on the neighboring lot don't automatically have full use rights to the access road beyond the entrance to their lot unless they have a specific easement granting them those rights. In California, an easement grants someone "a limited right to use another's land for limited purposes" - most commonly as a right of way over another's property. Without such an easement, they would typically only have the right to access their own property.

When someone does have an easement, they generally "have the right to use every square inch of land that the easement is located on," and the property owner cannot prevent their use unless the easement holder agrees. However, this applies to people who legally hold easement rights - not to individuals who are staying on a property illegally. The situation you're describing involves people who are violating code enforcement rules, which likely affects their legal standing regarding road usage rights.

You might want to document this ongoing situation alongside the code enforcement violations. While property owners can post "No Trespassing" signs to protect against unauthorized access, these don't override legitimate easement rights - but may help establish boundaries for those without legal claims to the property. Since code enforcement has already identified six violations, consulting with a real estate attorney familiar with Shasta County regulations would give you specific guidance on limiting their use of the access road while the enforcement process unfolds.