Simplify the following text for a Grade 6 native English-speaking person.
Original: Its walls are near vertical cliffs up to 600m high and the Zanskar River ( a tributary of the Indus ) is only 5m wide in places .
Simplified: Its walls are near vertical cliffs up to 600m high . The Zanskar River ( a tributary of the Indus River ) is only 5m wide in places .