Route 4 is a short path in north Kanto from the eastern exit of Mt. Moon in the west to Cerulean City in the east. Though the official western terminus of Route 4 is at Route 3 south of Mt. Moon's western entrance, the western terminus is regarded by most to be Mt. Moon's eastern entrance.
From Mt.Moon, Route 4 travels to the east, swerving to the north and the south to avoid ledges along the route. The path turns north, then east near a large clump of trees surrounding a grassy area. To the east of this area is a ledge that separates Mt. Moon from Cerulean. By hopping down this ledge, the trainer cannot return to the previous towns until they travel through Diglett's Cave and use HM01 (Cut) on Route 2, or use HM02 (Fly) to return to the cities.
The majority of the route is fairly straightforward as there is only one true way to proceed on the path and there are no trainers to battle (with the exception of a Lass on the highest hill on the route; however, she is reached only by way of the waterway that begins on Route 24).
A Poison-type Pokémon that is exclusive to Pokémon FireRed. Its Intimidate ability is quite useful: it decreases opponents Attack. It evolves into Arbok. It is rather mediocre Pokémon since its base stats aren't that good and it doesn't learn many powerful attacks by itself.
A Ground-type Pokémon that is exclusive to Pokémon LeafGreen. It evolves into Sandslash, which packs a punch. It has nice Attack and Defense stats, but its Special Defense and Speed are quite low. It learns some useful attacks by TMs.
Pokémon Purchase
In the Pokémon Center in the beginning of this route there is a fisherman that will sell you a very special Pokémon for 500 Pokédollars. At first it is the weakest creature in the entire game, with pitiful stats and only two possible moves (one of which is useless). When it evolves, however, it becomes one of the most invaluable and fearsome colossi of all the Water-types: Gyarados. Seeing as you can fish for Magikarp when you get the old rod a little later, this is still a rip-off.