After defeating Roark, head west from Oreburgh City onto Route 207. You'll encounter Professor Rowan's assistant again, who will give you the Dowsing Machine app for your Pokétch. This app helps you find hidden items. There are a few trainers on this route, so battle them to gain experience. At the end of Route 207, you'll reach the entrance to Mount Coronet.
Mount Coronet is a significant landmark in Sinnoh. For now, you'll only be traversing a small section of it. Use Rock Smash (if you have a Pokémon that can learn it and you've taught it the move) to clear any boulders blocking your path. The path through Mount Coronet is linear at this point. You'll encounter various Rock and Steel-type Pokémon here. Exit Mount Coronet to the north, which leads you to Route 208.