The area you are trying to go to is part of the Ghostlands. You cannot fly in that zone and cannot fly your mounts into it was put in as an instance so Blizzard would not have to redo the entire world to make it fit. You have noticed that no flying in the starter BC zones and unless you use a portal, Boat, Port, or instance entrance you cannot enter that zone.
Thrumbar
You need to go to Ghostlands to uncover that area....
