archive block - how to sort with most recent months at the top

By default the drupal blog archive block listing shows the oldest month at the top.

To change to sort with recent months at the top, don't change sort criteria.  Instead, change argument.  Argument view listing shows what to do if default argument isn't available.  Default setting is to show summary, sorted ascending.  Change this to show summary, sorted descending to get most recent months at the top.