Abstract The California ribbed mussel, Mytilus californianus, is an ecosystem engineer crucial for the survival of many marine species inhabiting the intertidal zone of California. Here, we describe the first reference genome for M. californianus and compare it to previously published genomes from three other Mytilus species: M. edulis, M. coruscus, and M. galloprovincialis. The M. californianus reference genome is 1.65 Gb in length, with N50 sequence length of 118 Mb, and an estimated 86.0% complete single copy genes. Compared with the other three Mytilus species, the M. californianus genome assembly is the longest, has the highest N50 value, and the highest percentage complete single copy genes. This high-quality genome assembly provides a foundation for population genetic analyses that will give insight into future conservation work along the coast of California.