The Th220 level scheme has been considerably extended from an experiment using the Mg26+Pt198 reaction at 128 MeV. The evaporation residues from this very fissile system were selected with the HERCULES detector system and residue-gated γ rays were measured with Gammasphere. The simplex feature (alternating-parity levels) persists up to the highest spins observed (23), but the nucleus exhibits a more vibrational-like behavior than the heavier Th isotopes. In addition, a doubling of the negative-parity, odd-spin states is seen as well as a staggering of the B(E1)/B(E2) ratios. A new interpretation based on a picture of tidal waves on a reflection-asymmetric nuclear surface is proposed.