I obtained a Level 50 Groudon, and based on leveling it to 100, checking the Move Relearner, and past games, its full level up movepool is likely the following:
Start - Mud Shot
L5 - Scary Face
L15 - Lava Plume
L20 - Hammer Arm
L30 - Rest
L35 - Earthquake
L45 - Ancient Power
L50 - Eruption
L60 - Bulk Up
L65 - Earth Power
L75 - Fissure
L80 - Solar Beam
L90 - Fire Blast