It's superwash. It's merino. And it is hand dyed in Colorado, using natural plant dyes.
The one downside I found is that it turned my hands blue, and made my tension hand itch. That being said, I've used lots of other colorways of this stuff, and this is the first that has bled or made me itch, so I really think that both are just the indigo. That being said, the finished socks didn't bleed in the blocking bath, and when I wear them they don't turn my feet blue, so the bleeding is not horrible, and again... if it bothers you pick an indigo free color. On a related note, I may be allergic to indigo, and that pisses me off.
These socks (Aspen) are currently available for preorder in my Ravelry store! They are also included in my new ebook, Home State Botany: Colorado.