Instructions
Defeat Wattson in the Mauville Gym to obtain the Dynamo Badge. Head north from Mauville City and defeat the trainers as they confront you.
Ride the Mach Bike across the desert sands and head west onto Route 113. Defeat any trainers who challenge you.
Continue west to reach Fallarbor Town. Head west onto Route 114 and continue on to Meteor Falls.
Defeat Fisherman Nolan in battle and enter the house beside him. Talk to the boy inside of the house to obtain TM28, which contains Dig.