Walkthrough: Connected to Poni Plains is the Poni Coast, which connects Poni Plains to Poni Gauntlet. It's a pretty empty area, outside of a given trainer here and there.
Wild Pokemon:
Rustling Spots (Levels 56-59): Dugtrio(100%)
Trainers:
Sightseer Steve - Level 59 Exeggutor
Punk Girl Reika - Level 59 Exeggutor
Youth Athlete Anton - Level 58 Sandslash
Sightseer Devin - Level 59 Geodude, Level 59 Graveler, Level 59 Golem
Sightseer Noriko - Level 59 Ninetales, Level 59 Sandslash
Firefighter Aiden - Level 60 Octillery, Level 60 Clawitzer
Items:
TM97 - Western Cliffside
Power Bracer - Near Firefighter Aiden
Max Revive (Hidden) - Near Youth Athlete Anton