To get from the California border down to Mexico, you would get service off 
of SoCalGas' and SDG&E's tariff (i.e., you have to wheel through SoCalGas and 
SDG&E to get there.  There may be a single tariff for that service, however 
(rather than taking service off of two tariffs).  I'll try to get the tariff 
numbers and get back to you.  All the tariffs are on Sempra's website.

Best,
Jeff