Not to be mean or anything... but I think you just answered your own question! Go running <b>on the mountain</b>! That will give your legs a much better workout than running on flat land will.
It might not be exactly what you are going to do for the track team, but if you can run a mile uphill in 6 minutes I am sure you could run one around a track in 4:30.
Think about Rocky 3(?) when he is fighting the Russian and trains in the wilderness. He runs up hill in the snow. I know it is a fictional movie, but the concept is the same. If your body is used to doing something hard and you only want it to do 50% of that, you are much better off than the other way.
Just make sure you run during daylight so that you can see the rocks and not hurt an ankle or something.
Good luck with track!