Question about let binding behavior

[Louis-Guillaume Gagnon]

Dear all,

I'm a long time user but I've only recently started to dive into elisp 
programming. I'm a bit surprised by the following behavior.

Let's say I write the following silly function:

(defun foo (bar)
   (let ((baz '((quux . 0) (quuz . 0))))
     (if (> 10 bar)
     (setcdr (assoc 'quux baz) bar)
       (setcdr (assoc 'quuz baz) bar))
     baz))

Then the following evals:

(foo 1)
=> ((quux . 1) (quuz . 0))

(foo 100)
=> ((quux . 1) (quuz . 100))

I'm surprised that the list is not reset since I thought the binding was 
local to the function, but clearly I don't have the right mental model 
for elisp evaluation. For the actual application I ended up using 
copy-tree but I'd like to understand this better -- could someone 
explain or point out the relevant sections of the manual?

Cheers,
L-G

P.S. Please keep me in CC, I'm not subscribed to this list