From a line of four and from "Centers In" or "Centers Out" lines in which the inside pair can California Twirl: Centers arch and the ends duck thru then Zoom. Arching couples always California Twirl. A regular line finishes with one couple behind another. A Centers In or Centers Out line finishes with couples facing.
Vern Callahan 1965
This definition is from The Handbook of Modern Square Dancing by Jay King.
It is provided here for informational and educational purposes only.