It being a whole cloth makes a lot of sense actually.
There are patterns out their for spirals though.
And here is another quilt that is pieced that has the same look:
http://www.debplestid.ca/quiltssale.html (third one down the page). It is more close up and easier to see the pattern. You could always email the artist and ask if there is a pattern for sale.
And another at this link -- also a dyed wholecloth:
http://www.oac.state.oh.us/riffe/exh...e&Take/G&T.asp (4th row middle)