a deep, narrow valley with steep sides that may have a stream flowing through it
Sentences:
NASA Earth scientists study
canyons and how they were made.
Our family went to the Grand
Canyon in Arizona during summer vacation.
More Information:
http://www.nasa.gov/multimedia/imagegallery/image_feature_769.html
http://www.nasa.gov/multimedia/imagegallery/image_feature_83.html
http://www.nasa.gov/mission_pages/MRO/multimedia/pia09097.html