Zion Canyon is relatively wide in the lower reaches because the layers beneath the Navajo Sandstone are easily eroded, undercutting the high cliffs and causing rockfalls. It's where the Virgin River flows entirely in Navajo that the canyon gets incredibly narrow and very deep, with vertical walls reaching 2,000 feet above the river. The Riverside Trail is a paved ADA accessible trail that follows the narrowing canyon, ending after a mile at the entrance to the Narrows, where no trails are possible, but people can explore miles upstream as long as they don't mind getting wet numerous times.
I'm sorry to tease you with the picture though. It's actually a Turkey Vulture. The ranger hadn't seen any this season yet. The upper canyon is also a good place to watch for Peregrine Falcons.