Simplify the following text for a Grade 9 native English-speaking person.
Original: The area extends from Port Roper on the Gulf of Carpentaria around the coast to the East Alligator River , where it adjoins Kakadu National Park .
Simplified: Arnhem Land goes from Port Roper on the Gulf of Carpentaria around the coast to the East Alligator River where it joins Kakadu National Park .