As I said in the guide right before this one, the best place to raise your Gathering skill from 250 - 270 is the Salix Logs that are scattered around the Mosbear Snowfield. This location is actually part of my Farming locations guide, since there is such an abundance of Salix Logs over here.
Once you reach 270 with your skill you will want to switch locations. From the Mosbear Snowfield you will want to head far southeast to the next area. Below is a picture of where you can find this area on my map:
Over here you will find a herb called Calamot. You will want to gather this herb until you reach skill level 280. Once you reach 280 you will want to head north.
Just east of the Besfer Refugee Camp you will find Almeha. When I say Almeha I mean a fuck load of it. They are clams that are scattered along the whole "beach area". There are quite possibly 100 or more of them all over this beach. The Clams will take you up to skill level 299. Once you get 299 you will need to return to Pandemonium and train your Extract Vitality to 300.
NOTE: Almeha is also one of my favorite farming locations since the clams are used in a popular cooking recipe for casters, Almeha Aether Egg-rolled Sushi. Below is a video of me farming Almeha.