I took pictures at this same spot; they're posted on the Ruby Mountain page I put up recently. I think it's from calcium; the rocks feel chalky if you touch them. Anyway, it's among the prettiest streams I've ever seen.
"After the first glass, you see things as you wish they were. After the second, you see things as they are not. Finally, you see things as they really are, which is the most horrible thing in the world."
--Oscar Wilde on Absinthe