[special-K]

I never knew why. But,actual west coast mirrors are what you saw on big trucks for years with a tall rectangular head and mounted using upper and lower arms. The first truck mirrors were just small round heads,or maybe slightly bigger rectangles,on a single arm. For ample rear vision these mirrors extended far off the cab.Not only did the small heads give poor rear vision,they also vibrated really bad,as you can imagine. Years ago,before interstates,trucking was somewhat divided between coasts and what they drove and did on one coast differed from the other in many ways. I figure it was the trucks on the west coast that started running the larger/better mirror design and that's where the name came from. GM offered real west coast mirrors as Sr West Coasts and a mini version on 67/68 10-30s. They also gave the "west coast mirror" name to the tripod style mirrors that came on these trucks,but they really aren't actual west coast mirrors