Stone pillars can generate underneath a mesa/badlands biome below y=0, or on any caves, especially underneath an eroded badlands biome.
Step to Reproduce
1. Create a new world with the seed 218785
2. Go to the coords to /tp -253 -9 -62
The caves inside don't generate with stone pillars.
The caves have strange stone pillars inside, below y=0.
Large stone pillars are generated below -y and if on the surface there is a plateau biome