Please do the following:

1.First Complete Badges
2.Defeat Pokemon Leage and Champion Wallace
3.Get Rayquaza (Sky pillar) Kyogre and Groudon (showed in the bottom hot to) <- not required ass long ass you have pokemon to defeat 6 lvl 74-78

To get both Goudon and Kyogre

You must go to the weather institute and talk to the prof.in the second floor and he will say Drought-Groudon or Heavy Rain-Kyogre and he will also say what route then find a Cave-Groudon or Deep area-Kyogre and there you will find them
(Well Suggested Stevens team has many weak against fire and water)

CAUTION!:They are both LEVEL 70

Lets continue:

4.Go to Fallabor
5.Go to Meteor Falls
6.Go up the Waterfall
7.Go inside the cave and climb the ladder
8.Go to the Bottom ladder and climb it
9.Go inside the cave
Final Step:Ill give you directions:

Right
Left
Straight up
And there you have it Steven facing the rocks