Original: The Cascade Arc includes nearly 20 major volcanoes, among a total of over 4,000 separate volcanic vents including numerous stratovolcanoes, shield volcanoes, lava domes, and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas.
Simplified: It includes about 20 major volcanoes, among a total of over 4,000 separate volcanic vents.