if your at the top of the mountain, and you turned the power back on (by helping the electricion het his keys), then you need to travel back down the mountain to the first cavern (where the guy who sent the electriction up the mountain is), and use the big cannon (which was out of power before), and that will take you to the "shinny rock" that Rachel refered you too.
whats wrong with the exit placement? The cannon inside the hill (the one that your supposed to turn the power on for) will blast you straight to that spot.
I can add another character on the top of the hill if it would make that clearer.
edit: Power of posting! :D Now let's go on.
edit2: I did it with an awesome score! :D