• The river is flowing through rock in all three pictures.
• The land gets deeper and narrower over time.
• The river carries sediments as it moves.
• The middle image shows eroded sediments at the bottom.
• The final image shows a deep canyon with steep sides.

EXTENDING THE DISCUSSION
After the observational question, randomly call on one or more students to share what they or their partner answered. Then ask the class, “Did anyone notice…?” using the suggestions above or anything else you’ve noticed.

• How long does it take for a canyon to form?
• What causes erosion to happen faster or slower?
• How does weathering help break down the rock first?
• What happens to the sediments after they are carried away?
• Can wind or ice also help form a canyon?

EXTENDING THE DISCUSSION
After students have shared what they notice, ask the class, “Did anyone wonder…?” using the suggestions above or anything else you might think is interesting or relevant to the lesson.

To the observational question, How does a canyon form?

LOW-LEVEL

A canyon forms by a river cutting into the rock.

HIGH-LEVEL

A canyon forms by water causing weathering and erosion, which break down rock and carry away sediments over a long period of time.

RESPONDING TO RESPONSES
Emphasize and celebrate each student’s use of the key vocabulary to support a culture of “no wrong answers.”