*wiggles my fingers in your face like some hoodoo woman* TOTES PSYCHIIIIIC!
Psh, not even. I made an educated guess. The green-grey pony has a messy design so I'm assuming they do dirty work. Their cutie mark is two bushes and a pine tree which leads me to believe they're involved in forest work. I don't think the group is anywhere near a steep mountain and running towards any would take too long. If Duster can't fly then the only option left is down. Straight down like the cellars people use to escape tornados. Considering the last panel has this new green-grey pony in a diving position I can assume they're all making a dive to safety. Plus, I know enough about you at this point to understand you think out the box and take every opportunity to put elements of unusual interests, designs, and ideas into your characters. A burrow using pony is totally something you'd be able to come up with. Major props, Mach.