You're all wrong. The thread is asking about an apostrophe-s, possessive case.
maybe Sierra Cement's original post had the title wrong
did he mean
(A) Sierra or Sierra's
or
(B) Sierra or Sierras
if A, then Jeff is correct about possessive.
if B, then all the other comments flow from there.
Of course, Sierra is lazy for Sierra Nevada.
Would those who (incorrectly) say
"I have been to the Sierras"
actually be saying:
"I have been to the Sierra Nevadas"?
Never heard that, just Sierra Nevada mountains (redundant)
I am surprised this thread has legs. I am guilty, too.
Edit: This just in from CNN
This historic drought demands unprecedented action," Brown told reporters, standing on a patch of dry, brown grass in the
Sierra Nevada mountains that is usually blanketed by up to 5 feet of snow.