If you were to go to a local department store to ask for a "California king comforter," you might feel that you had provided the opening line to a long-running bedding joke. Quite possibly, the store clerk would tell you that there is no such thing as a California king comforter at all, and ask what it is that you are talking about. That happens all the time. Of course, the store clerk likely would know that you were referring to a comforter for a California king-sized mattress--it is just that there are few opportunities for humor when selling bedding is your profession. Many sellers of bedding simply deny that there is a "California king-sized" when it comes to comforters, reserving the term for mattresses.
It does appear that some retailers do understand "California king sized" to refer either to mattresses of a certain size, or to bedding of an appropriate size for such mattresses. But you might say that it is bad form to even speak of a "California king comforter," and that you ought to just request a comforter for a California king mattress.
We have seen that the term "California king comforter" derives from the term "California king mattress" or "California king-sized mattress," which is, in turn, often simply shortened to "California king." There is also an "eastern king," which is shorter and wider than the California king, where the term refers to the east coast of the United States.
"California king-sized mattress," "California king" and "Cal-king" are interchangeable terms. Such mattresses are most commonly found in the state of California.
David Bergeson invented the California king mattress in 1982. He lived in Concord, California, located in the San Francisco bay area. Presumably, his location had something to do with his choice of terms, but we can also imagine that using the term "California king" for an extra-long mattress was a way of suggesting the greatness of his home state, while also marketing something meant to be "little better" than the "standard," "eastern" king-sized mattress.
It may not always be possible to get a comforter designed specifically for a California king mattress. However, sometimes the standard king comforter will work.