Walkthrough
At the end of Route 9 is Route 10, a very small path that will lead you to Rock Tunnel on your way to finding the next Pokemon Gym. The Power Plant, home of the Legendary Pokemon Zapdos, can also be found on Route 10. Unfortunately, you need HM Surf to reach the Power Plant, making it inaccessible this early in the game. Head to Rock Tunnel instead.
Wild Pokemon
Grasses:
Voltorb (40%): Levels 14-17
Spearow (35%): Levels 13-17
Ekans(FireRed)/Sandshrew(LeafGreen) (25%): Levels 11-17
Surfing:
Tentacool (100%): Levels 5-40
Magikarp (100%): Level 5
Horsea(FireRed)/Krabby(LeafGreen) (60%): Levels 5-15
Krabby(FireRed)/Horsea(LeafGreen) (20%): Levels 5-15
Magikarp (20%): Levels 5-15
Horsea(FireRed)/Krabby(LeafGreen) (84%): Levels 15-35
Gyarados (15%): Levels 15-25
Psyduck(FireRed)/Slowpoke(LeafGreen) (1%): Levels 25-35
Pokemon Trainers
Picnicker Heidi: Level 20 Pikachu, Level 20 Clefairy
Picnicker Carol: Level 21 Pidgey, Level 21 Pidgeotto
Hiker Clark: Level 21 Geodude, Level 21 Onix
Hiker Trent: Level 19 Onix, Level 19 Graveler
PokeManiac Herman: Level 20 Cubone, Level 20 Slowpoke
PokeManiac Mark: Level 29 Rhyhorn, Level 29 Lickitung
Pokemon Trainers - VS Seeker Rematch
Hiker Trent: Level 31 Onix, Level 31 Graveler
PokeManiac Herman: Level 29 Marowak, Level 29 Slowbro
PokeManiac Herman: Level 54 Marowak, Level 54 Slowbro
PokeManiac Mark: Level 33 Rhyhorn, Level 33 Lickitung
PokeManiac Mark: Level 54 Rhydon, Level 54 Lickitung
Items
Super Potion: ItemFinder
Persim Berry: ItemFinder
Cheri Berry: ItemFinder
Nanab Berry: ItemFinder
Max Ether: ItemFinder