They include the mountains and plateaus of northern Kashmir, the Himalayas proper and the hills of Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura and Meghalaya.
They are divided into three groups. They are
 The Himalayas
 The Trans-Himalayas
 Purvanchal or the hills of the North-East.
 The Himalayas
This is the highest mountain range of the world.
It extends in the shape of an arc for a distance of about 2500 km from west to east along the northern boundary of India between the Indus gorge in Jammu and Kashmir in the west and Brahmputra gorge in Arunachal Pradesh in the east.
The breadth of the Himalayas ranges between 400 km in the west to 150 km in the east.
The area covered by this mountain system is about 5 lakh square km.
It has three major ranges.
These ranges are separated by deep valleys and plateaus.
The southern slopes of Himalayas facing India are steeper and those facing the Tibetan side are generally gentler.
In the east, Himalayas rise almost abruptly from the plains of West Bengal and Assam.
That is why two of the highest peaks of Himalayas, Mt. Everest (in Nepal) and Kanchenjunga are not very far from the plains.
On the other hand, the western part of Himalayas rises rather gradually from the plains.
Hence, the higher peaks in this part are farther from the plains and a number of ranges lie between the plains and high peak.
The high peaks of this part such as Nanga Parbat, Nanda Devi and Badrinath are very far from the plains.
Three parallel ranges can be identified in the Himalayas.
[b] Himachal and
[a] Himadri (Greater Himalaya)
This is the northern most and the highest range of the Himalayas.
This is the only range of the Himalaya which maintains its continuity from west to east.
The core of this range is made up of granite rocks and flanked by metamorphic and sedimentary rocks.
The extent of this range is between the Nanga Parbat peak (8126 m.) in the west and Namcha Barva peak (7756 m.) in the east.
The average height of this range from sea level is about 6100 metres.
Over 100 peaks have a height of more than the average height of the range.
The highest peak of the world, Mount Everest, (8848 m) is situated in this range.
Kanchenjunga, Makalu, Dhaulagiri, Annapurna are some of the other peaks having a height of more than 8000 metres.
Kanchenjunga is the highest peak of Himalayas in India.
The Himadri range is snow clad throughout the year.
There are a number of large and small glaciers.
After melting of snow and ice, their water falls in the rivers of northern India making them perennial throughout the year.
Gangotri and Yamunotri are good examples of such glaciers.
The Himadri range can be crossed through some passes like Zojila, Shipkila, Niti, Nathula etc.
[b] Himachal (Lesser or Middle Himalaya)
It is located southwards of Himadri.
The breadth of Himachal range is 60 to 80 km and the height varies from 1000 metres to 4500 metres.
Some of the peaks of this range have a height of more than 5000 metres.
This range is highly dissected and uneven.
This range mainly consists of metamorphosed rocks.
The gentle slopes of the eastern part of this range are covered with dense forests.
The south facing slopes of other parts of this range are very steep and generally devoid of any vegetation.
The norths facing gentle slopes of this range are covered by dense vegetation.
Pir Panjal in Jammu &Kashmir and Dhauladhar in Himachal Pradesh are the local names of this range.
The beautiful valley of Kashmir extends between the Pir Panjal and Himadri ranges.
The famous valley of Kullu and Kangra are also a part of Himachal ranges.
Most of the hill towns or resort towns are located in the Himachal range.
Shimla, Nainital, Mussouri, Almora and Darjeeling are some such famous hill towns.
[c] Siwalik (Outer Himalaya)
The southernmost range of Himalayas is known as Siwalik.
The Himadri and Himachal ranges of the Himalayas have been formed much before the formation of Siwalik range.
The rivers rising in the Himadri and Himachal ranges brought gravel, sand and mud along with them, which was deposited in the rapidly shrinking Tethys Sea.
In course of time, the earth movements caused folding of these relatively fresh deposits of sediments, giving rise to the least consolidated Siwalik range.
The average height of the Siwalik range is very low, about 600 metres only.
There are some broad valleys in between the Himachal and the Siwalik ranges.
These valleys are known as ‘duns’.
Dehradun valley is one of the best examples.
 The Trans Himalayas Ranges
There are some mountain ranges to the north of the Himadri in Jammu and Kashmir.
The range extending to the north of the Himadri and running parallel to it is called the Zaskar range.
North of Zaskar range is the Ladakh range.
The river Indus flows towards northwest between Zaskar and Ladakh range.
Many scholars treat Zaskar and Ladakh ranges as parts of the Great Himalayas and include them in Kashmir Himalayas.
North of the Ladakh range lie the Karakoram.
The name of the Karakoram in Sanskrit literature is Krishnagiri, K2 (8611m) is the highest peak of the Karakoram Mountains.
This is the second highest peak of the world, next only to Mt. Everest.
Ladakh plateau is situated in the north eastern part of the state of Jammu &Kashmir.
This plateau is a very high and arid. It forms one of the remote areas of our country.
Purvanchal is the name given to all the hills of north east India beyond Brahmaputra gorge.
The average height of these hills from sea level is 500 to 3000 metres.
These hills are located in Southern Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura and Meghalaya.
Mishmi, Patkoi, Bum, Naga, Manipur, Mizo(Lushai) and Tripur are the major hilly ranges of this region.
Meghalaya Plateau is also part of these hills of the north eastern region.
This plateau includes the hills of Garo, Khasi, and Jaintia.
Structurally, however, it is a part of Peninsular India.