Fossil (?) of spine or backbone whale (?)

I found this old bone in my garage 40 years ago, when I bought this old house on Whidbey Island. I have almost thrown it away a number of times, but instead put it on my bookshelves a couple of years ago. Now I am curious about it. Anybody have an idea what kind of animal it is from. I am guessing that it is from a whale, as they swim by in front of my house and have been for eons. Don't know who found it or when, as the old place is 100 years old now. Could have been any of the two previous owners. Appreciate the help. Thanks.
PS: it measures 9" across and 4.5" high approximately. Didn't weigh it.