While most basic-plumaged Common Murres (Uria aalge) show white facial plumage and tips to the secondaries, some individuals of central California from September through November have dark faces and secondaries. To investigate the plumage state and age of such birds, I examined specimens and photographs of Common Murres taken off central California and conclude that outgoing and incoming alternate feathers as well as early-replaced and late-replaced dark basic and formative feathers all may contribute to this variation. Hypermelanism may account for a small proportion of cases. The early onset of prebasics molting—before hormone signaling switches from dark feathers typical of the alternate plumage to white feathers typical of the basic plumage—may be responsible for most of the darkest-faced birds in basic plumage. This type of asynchrony of molt and the signal for change in plumage appears to occur more often in second-cycle birds, which initiate the prebasic molt earlier than do older adults, and it may also explain plummages in chicks and juveniles molting during May and June. Common Murres in basic plumage from colonies in central California appear to acquire dark facial feathers more often than birds from more northerly colonies, which could relate to earlier breeding and molt in central California.