This is a wonderful place to bring you dog to run around! You can bring your mountain bike or just walk the myriad trails of the park. I've laid out a track in this guide that will bring you to the furthest extents of the park and out to the shore of the mighty Columbia River where your dog can play in the water and cool off on a hot summer day.
Take Exit 18 off of I-84 east of Portland, OR. Parking is on the north side of the highway and is free.