What mountain range stretches 2400 km westward from a peak called nanga parbat to one called namcha barwa?

The mountain range in question is the Himalayan Mountain Range.

Nanga Parbat (locally known as Diamer) is considered the westward anchor of the Himalayan Mountain Range. It is located in Pakistan, more specifically in the Diamer District of Gilgit Baltistan region of the country. This is on of the highest mountain peaks in the world, more precisely it takes the number nine spot by height with its 8,126 meters above sea level.

Namcha Barwa (also referred to as Namchabarwa) is considered the eastern anchor of the Himalayan Mountain Range. It is located in Tibet as part of the Tibetan Himalaya. It is not as high as Nanga Parbat but its height of 7,782 meters above sea level is still an astounding height.