This is gotten easily during a campaign race.
In the 'dry rigs' zone, there is a campaign race 'Way of the lumberjack'.
Before the first checkpoint just after you start the race you will take a few corners up hill, the jump is shortly after. You can't miss it.
You will need to use a fast bike (when you unlock one. I used the 'Valkyrie' personally), for you to make the jump far enough.