You have to get up the rope way at Mt. Chimney just ten or more steps away from the desert above Mavile City.. Then you will arrive at the hills. You have to battle with the Team Magma grunts and you will get the Meteorite. Then, you will have to get down the rocky paths and you will arrive at a small town. Don't go right because you will get down the city if you do so. Go left and you will find yourself at the Lavaridge Town where the 4th gym is located. Hope the above notes do help you. Good luck in your Hoemn days.