After you battle Team Aqua/Magma on Mt. Chimney and defeat their leader, you retrieve the Meteorite and continue to Jagged Pass.
In the grass in this area, you can catch Machop, Numel, and Spoink.
Go south. There are ledges that you have to jump down, but if you have the Acro Bike, you can jump up the small rocks in the walls. You have to hold down the B button until the bike starts jumping, then you can jump up those rocks.
Southwest from the Mt. Chimney exit, there is a hidden Full Heal in the grass.
You can use the Acro Bike to jump down the rocks along the east side, which allows you to avoid the trainers. You can also get a Burn Heal next to a big tree on the east side of the path.
In the western part, you encounter Hiker Eric. In Ruby and Sapphire, he has two level 21 Baltoys, and in Emerald he has a level 20 Geodude and level 20 Baltoy.
In Emerald, there is a Team Magma Grunt who has level 22 Poochyena and level 22 Numel.
Farther south, you find Camper Ethan, who has Zigzagoon and Taillow.
There is also Picnicker Diana, who has a Shroomish, Oddish, and Swablu.
Emerald also has Triathlete Julio, who has a level 21 Magnemite, and Picnicker Autumn, who has a level 21 Shroomish. Julio and Autumn might team up for a Double Battle against you.
If you have the Acro Bike, then near the south end of Jagged Pass, you can use the Acro Bike to hop up to the second ledge and find a hidden Great Ball to the left.
When you are ready, go south to reach a previously inaccessible area of Route 112. Don't jump down the ledges to the east unless you are prepared to go through Mt. Chimney and Jagged Pass again. Instead, go west to Lavaridge Town.