Chapter 
Organize
Learn
Connect
Instructors now have an easy way to collect students’ online quizzes with the Norton Gradebook without flooding their inboxes with e-mails.
Students can track their online quiz scores by setting up their own Student Gradebook.
Chapter 21: Dry Regions: The Geology of Deserts
Animations
Click on the links below to view animations created specifically for Earth: Portrait of a Planet. Animations require Macromedia's Flash Plug-in.
Zoomable Art: The Desert Realm
Except in the case of large rivers, such as the Nile or the Colorado, which bring water into a desert region from a more temperate region, streams in deserts fill with water only after heavy rains. At other times, the stream channels are dry. These channels are called dry washes, arroyos, or wadis. For more information, see the Featured Painting on pp. 748-749 in your textbook.