Simplify the following text for a Grade 9 native English-speaking person.
Original: The range is mostly located in the United States but extends into southeastern Canada , forming a zone from 100 to 300 miles ( 160 to 480 km ) wide , running from the island of Newfoundland 1,500 miles ( 2,400 km ) south-westward to central Alabama in the United States .
Simplified: They form an area from 100 to 300 miles wide , running 1,500 miles from the island of Newfoundland in Canada to central Alabama in the United States .