Those recommendations are fine....however, downtown Portland is a wonderful urban area. Well worth exploring. It is my favorite city on the west coast.
That said....June is rather late for waterfalls in the Columbia Gorge. Quite frankly, I would wait for a major storm to hit Portland and then show up just after the storm. There are lots of minor falls that only run after major storms that are more interesting than the known waterfalls.
You might want to check with the Forest Service which manages the Columbia Gorge for additional information.
There is also this website:
http://www.waterfallsnorthwest.com/nws/