Ordering YYYY MM DD in reverse chrono order

Hello,

I am trying to select distinct dates and order them in the reverse
chronological order.  Although the column type is TIMESTAMP, in this
case I want only YYYY, MM, and DD back.

I am using the following query, but it's not returning dates back in
the reverse chronological order:

SELECT DISTINCT
  date_part('year', uu.add_date),  date_part('month', uu.add_date),
  date_part('day', uu.add_date)

FROM uus INNER JOIN ui ON uus.user_id=ui.id INNER JOIN uu ON
ui.id=uu.user_id
WHERE uus.x_id=1

ORDER BY
date_part('year', uu.add_date), date_part('month', uu.add_date),
date_part('day',  uu.add_date) DESC;


This is what the above query returns:

 date_part | date_part | date_part
-----------+-----------+-----------
      2004 |         2 |         6
      2004 |         4 |        20
(2 rows)


I am trying to get back something like this:
2004 4 20
2004 4 19
2004 2 6
...

My query is obviously wrong, but I can't see the mistake.  I was
wondering if anyone else can see it.  Just changing DESC to ASC, did
not work.

Thank you!