From Fodors.com article:
The Watchman Campground at Zion National Park fills up months in advance, and for good reason: This massive 176-site campground located a 1/4 mile from the south entrance and visitor center sits in the shadow of the iconic Zion rock formation. Despite its size, there’s enough space between campsites, spread out among six loops, to preserve your camping experience. For something more private try one of the 18 walk-in sites at the campground. In addition to firepits and clean bathrooms with flush toilets, some of the sites have shade trees to relax under after a long, hot day of traversing the The Narrows.