Simplify the following text for a Grade 6 native English-speaking person.
Original: The Dry Tortugas are a small group of islands , located at the end of the Florida Keys , USA , about 70 m west of Key West , and 37 m west of the Marquesas Keys , the closest islands .
Simplified: The Dry Tortugas are a small group of islands , located at the end of the Florida Keys , United States . They are located about 113 k west of Key West , and 60 k west of the Marquesas Keys , at , the closest islands .