one chaco to rule them all
As already mentioned, despite having the same great fit and distinct sole/strap profile, the Yampa uses an entirely different outsole, which shaves a great deal of weight off its Unaweep brethren, making it just as perfect for crossing the street to get a newspaper, as it would for hiking a dry riverbed in Moab. The sole isn't as lugged or stiff as the aforementioned, but that makes the Yampa a little more versatile, and less of a chore to wear. Comfortable right out of the box, they broke in very quickly.
* if you're in-between sizes, I wouldn't recommend going up. my street shoe size is a 10.5, but the 10 here fits great