A Vintage Rosy Red Washita, manufactured sometime between the 1850's and 1930's, but probably in the earlier range as it appears to be hand cut.
These stones are surprisingly fast cutting for the keenness of the edge that they can produce, and blow modern Soft Arkansas Stones out of the water in both cutting speed and the edge they can produce.
They do wear/dish quite a bit faster though.
They're usually extremely expensive, but I took my chances with an unlabeled stone that looked to be a Washita, and scored the one I have on ebay for $15. I was lucky indeed.
I made a cool box for it, too -- chiseled out by hand from two pieces of Cypress.
Hmm... Seems like I can't upload images. I'll come back with pictures when I can maybe.