I dedicate this post to Fuzzy Lizzie over at The Vintage Traveler. She can tell you far more about Pendleton than I can, and if you look through her blog, you'll learn a lot about... well... a lot of things!
This, from 1957 Sports Afield:
I've always had a soft spot for plaid and for Pendleton. Talk about a quality clothing line (until recent years... as so many, they've moved production overseas... Again, see The Vintage Traveler for more!). If you think you want to give Pendleton to someone for Christmas, by all means, start looking sooner rather than later, because I highly recommend you seek out some vintage Pendleton. It is abundant because of its high quality. This stuff lasts and lasts, and it's as cozy as the day it was made in most cases.
There IS only one Pendleton (unless you're talking about my best college friend's family, in which case there are several "unique" Pendletons!). And it IS a hearty way to say "Merry Christmas"! I mean really...can you be any cozier than his-and-hers plaid wool robes? Now, I can't say what's with the heels and robe on herself up there...but whatever!