Not taking any chances, you tie a surveyor's tape to the nearest trunk, and tell Furia Storm that you should wait for Moonflower before attempting to cross the oat field.

You use Surveyor's Tape.

You both retrace your steps up to the road, and sit next to it. Thankfully, it doesn't take long before your bat pony companion finally catches up to you. She lands nearby, and you welcome her return.

Moonflower: "Sorry it took a while! Sea Swirl wasn't home, so I had to go lookin' for her. Did I miss anythin'?"

You tell Moonflower about your findings so far, and now with a full party, you make your way back to the oat field to pick up where you left off.

Moonflower: "Ooh, you're right! I can see a beaten track goin' through the oats from up here!"

Following your flying friend's directions, you and Furia Storm enter the tall grass, and trample yourselves a clear path. As you do so, you barely notice that far above, the last rays of sunlight slowly begin to fade away.

Moonflower: "Forward... forward... and stop! Careful, the track goes out into a mud slide, and those look like thorny bushes down below. Ya don't wanna get caught in those!"

You push aside the last of the oats in front of you, and find that you are standing on the edge of a long muddy slope. Imprints in the mud suggest that somepony did come down this way, and that it wasn't a fun ride.