Kevin,
Bolivia is completely operated by meter gauge. The network that connects Bolivia, also it connects to Chile, Argentina and Brazil. Not all of the trackage is still in service. The Argentina system has serious problems with mismanagement. There is something like 10,000 kilometers of track in the country. Less than 1/4 of the trackage is still in use. Also this is the only international routes in South America that goes from Atlantic to Pacific. There are many breaks in the routes that connect Argentina to Chile and Bolivia.
Only the standard gauge former General Urquiza Argentina route to Paraquay connect for international transfer. Brazil and Bolivia interchange but meter from Brazil to Argentina does not connect.
Colombia is three foot gauge. Ecuador is 42 inch gauge, but neither system connects to other countries.
Dale Brown