A mitochondrial DNA study has shown that the flying squirrels occurring on the Pacific coast of North America are distinct from Northern Flying Squirrels, with no evidence of hybridization in a zone of sympatry: (link). The authors call this cryptic species Humboldt’s Flying Squirrel (Glaucomys oregonensis).
Ben S, , North American, Glaucomys oregonensis, Humboldt’s flying squirrel, Northern Flying Squirrel, 0