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.
"After the first glass, you see things as you wish they were. After the second, you see things as they are not. Finally, you see things as they really are, which is the most horrible thing in the world."
--Oscar Wilde on Absinthe