A series of amphitheaters extends more than 20 miles (30 km) north-to-south within the park.
The largest is Bryce Amphitheater, which is 12 miles (19 km) long, 3 miles (5 km) wide and 800 feet (240 m) deep.

Bryce was not formed from erosion initiated from a central stream, meaning it technically is not a canyon.
Instead headward erosion has excavated large amphitheater-shaped features in the Cenozoic-aged rocks of the Paunsaugunt Plateau.
This erosion exposed delicate and colorful pinnacles called hoodoos that are up to 200 feet (60 m) high.

~ From Wikipedia