Simplify the following text for a Grade 8 native English-speaking person.
Original: The RhÃ ne drains almost the entire canton and flows in the main valley from east to west down to Martigny , then in a right angle north to its mouth in Lake Geneva .
Simplified: The RhÃ ne drains the main valley from east to west up to Martigny , Switzerland , then in a right angle north to its mouth in the Lake Geneva .