  In topological photonics, artificial photonic structures are constructed for
realizing nontrivial unidirectional propagation of photonic information. On the
other hand, moir\'e superlattices are emerging as an important avenue for
engineering quantum materials with novel properties. In this paper, we combine
these two aspects and demonstrate theoretically that moir\'e superlattices of
small-angle twisted monolayer-bilayer graphene provide a natural platform for
valley protected plasmons. Particularly, a complete plasmonic bandgap appears
stemming from the distinct optical conductivities of the ABA and ABC stacked
triangular domains. Moreover, the plasmonic crystals exhibit nonzero valley
Chern numbers and unidirectional transport of plasmonic edge states protected
from inter-valley scattering is presented.
