Check this out: http://www.sprintaquatics.com/prodinfo.asp?number=855

I stumbled on them while looking at different shoes mentioned in an older thread. I asked their customer support for more info, and they informed me those soled socks are about .3 oz and made of cotton/nylon. The might be too flimsy for creek crossings and probably won't dry out as fast as pure synthetic, but at four bucks I'm going to buy a pair or two and see how they measure up.