As a PS to my previous post, you can always call and reserve a permit for $15 for a specific date if you really want to make sure you'll have one; but I wouldn't waste my money, since walk-in permits are usually available.
CaT
If future generations are to remember us with gratitude rather than contempt, we must leave them more than the miracle of technology. We must leave them a glimpse of the world as it was in the beginning, not just after we got through with it.
- Lyndon Johnson, on signing the Wilderness Act into law (1964)
