Route 39 was first featured in Generation II and has not been featured since.
Route 39 is fairly linear as it is almost perfectly straight and has no major obstacles. There is only one patch of grass that contains wild Pokémon, and this area is located off the beaten path.
Along Route 39, there are four trainers: one near the entrance to MooMoo Farm and three near the southern end of the route. In Pokémon Gold and Silver, you can register the phone number of one of these three trainers, PokéFan Derek, into your PokéGear for subsequent battles, as well as the occasional Nugget if you have a Pikachu in your party when you battle him.
All of the items on Route 39 are concentrated near MooMoo Farm. Outside of the farm, a Berry tree contains a Mint Berry that will regenerate each day. Inside of the farm, you can purchase MooMoo Milk and obtain TM13, which contains the move Snore, once you restore the farm's Miltank to full health by feeding it a large number of Berries.