One-Myths: You do not need Rappeling gear, there is a cliff, but a side trail exists that allows you to avoid the cliff all together (We brought some gear, and while is was used on the cliff I felt bad for the person who had to carry it).
Two-Footwear: Wear shoes that are either meant to hike in water or shoes that don't have any special place in your heart (Teva, or Keens are my desired choice, though anything will work).
Three-Hydration: If at all possible bring a water filter, 9 miles hiking through desert and water can make anyone thirsty, and trust me when I say, you'll have plenty of water on the hike to filter (The particular water filter I own is a little more expensive than most but well worth the money it has a ceramic filter, and has a terricfic life span http://www.rei.com/product/695265).
Four-Apparal: Try to wear shorts that dry easily and are light, ie board shorts. Glasses and hats are preferrable but not needed (I also like to pack a pair of goggles, if you drop something in the water it's nice to find it again:) that really happened, and I used them).
Finally do not think that a 9 mile hike down hill is easy, this hike can kill you if you're not careful. There's reasons why permits are required for this hike, Just don't be stupid. Oh and one more thing, if you can, bring a digital camera, last time I did, and I've never regreted it. Use a ziploc to protect it from water.
Here are some pictures I took from last time we went.