Go to the part of the movie where the Raptor expert guy says, "Hush they're approaching the T-Rex paddock." The next scene shows the 2 cars. Look right by the tunnel the cars are coming out of -- there is a section of the fence missing.
I have seen that movie a thousand and one times, and I just noticed this the other day too when I watched it. The only explanation I could think of is that, maybe that is where the paddock ends and the fence could begin going up the mountain at that point. MAYBE.