In the very south region of
Noventarmas close the border the
Balaceras there is a mountain with the perfect spot for this achievement. (Picture 1 and 2)
Nearly on the top of this mountain you will find a gap with two "no slide" signs (picture 3). This is one of the best opportunities in the game. Take a little run up and start sliding by pressing and holding the
button. It is important that you only use your stick to steer left and right. Don't push the stick backward or forward!
Your slide should normally end just before the tree trunk with the blue bandage and the achievement should unlock (picture 4)
In case you need a video: