You will get arrested where ever you are found will be transported back to Napa County. There is no extradition unless you are arrested in a different state.
Depending on the type of warrant and circumstances, it may be possible for you to be arrested almost anywhere.
Johnny summed it up. Any law enforcement officer in the country with a computer in their patrol car can see you have a warrant. They'll arrest you and then you will be transported to Napa county to stand before a judge for the warrant.
The warrant will show up if they stop you and you will be taken into custody.
If Napa County will extradite, Sonoma County will hold you until Napa can pick you up.
