Can I use a 1 1/2 vent for a toilet (3" drain) in CA (not a went vent, no other fixtures on it)?
In California, which is based on UPC, a 1-1/2" vent, properly installed, can vent a 3" toilet drain.

However, local codes can vary, so it's always a good idea to draw a diagram and get a permit, so they can inform you of any special rules or anything you may have missed.