Their homes were very advanced in structure and design. They had good farms. There are two explanations generally given. The Indians may have left because of a severe drought that occurred in 1276-1299. They may also have been forced out by the Shoshonean, a tribe of raiders.
Nobody really knows for sure.
Whatever the reason whether it was a drought, the invaders or a combination of both the Anasazi left their homes, and all that remains there now are the magnificent cliff dwellings that fascinate and intrigue everybody who sees them. Finally, the student has stopped plagiarizing. The first two sentences could be considered general knowledge or conclusions the writer came to after a preliminary general reading, therefore not attributable to any particular source. The two reasons given by Donald Pike in the original paragraph have been clearly footnoted. Even the last sentence has been footnoted because the writer had used Pike's idea that the reason might be a combination of both.