Route 4 is an incredibly small route between Mt. Moon to the west and Cerulean City to the east. You can grab TM04 – Whirlwind in the northeast up some ledges.
Be careful, once you jump down the ledge to the southeast, you will not be able to return to Mt. Moon or the rest of Route 4 until after the third badge. When you’re ready to go on, head east to Cerulean City.