Awesome trip report!
I have descended that 400 foot monster. That entire canyon is an incredible adventure. VERY beautiful. The 400 footer is a two stage rappel. There is a ledge (room for 2 people) and a bolt about 150' down. Also, we used a trail just to the north of the canyon that will take you above the monster. From the road to the top took about an hour. I wouldn't do that canyon with a lot of water flow. We did it in October of 05.