I was there summer of '04, we stayed in a lakeside cabin. I remember that Park Lake had some rocks on the southwest end close to Highway 17 and a couple other random boulders. Nice resort with a heated pool, golfing, grocery store, café. There are a few spots for cliff jumping into the lake.
The Dry Falls visitor center is pretty cool and I think there is a shuttle to the Grand Coulee Dam for the laser light show. You will enjoy!