Most local places, you are lucky to find a spot on a Friday. However the more remote places like Yosemite and Yellowstone, where many of the campers are taking more than a weekend off work to visit the area, you will see they tend to fill up all week long.
Yes they will have more traffic on the weekends, but still are not the full to empty like some places near a larger town. It is more like full to 1/2 full on Sundays.
When I was in Yellowstone in 1994, they did not require reservations or even allow them at that time. By 2006, reservations where for each campsite and almost required. THe park rarely emptied in the summer time.
Bryce was another matter. I camped at Ruby's Inn and never have a problem getting a site in October. I like the full hookups and found the hot tub too!
Fred.
