Go to this site for more information and directions:
http://www.wta.org/go-hiking/hikes/dog-mountain
On your trip a great place to stop in for a bite to eat is Multnomah Falls Lodge.
http://www.multnomahfallslodge.com
I was extremely impressed with the Elk Burger. You may learn by following me that I am very fond of hamburgers. Good ones at least. There fries were spectacular as well. It's like they just cut a potato into wedges and put them in the oven. Along with some rosemary seasoning. Yum!!
If you aren't hiked out you could always hike up the Multnomah waterfall by the restaurant or enjoy the view from below.