The longitudinal valley lying between lesser Himalaya and the Shivaliks are known as

The longitudinal valleys lying between the Lesser Himalayas (Middle Himalayas) and the Shivalik Range are known as Duns (or Doon valleys).

These are structural valleys formed due to folding and faulting when the Himalayas were formed.
They are filled with alluvial soil and are often flat-bottomed and fertile, making them ideal for agriculture and settlement.

Dehra Dun (between Mussoorie and Shivalik ranges)

The Himalayas consist of three main parallel ranges:

The Duns occur between the Himachal and Shivalik ranges, running parallel to them.

These valleys are tectonic depressions formed due to folding during Himalayan uplift.