Alluvial soil is a type of soil that is formed by the deposition of silt, clay, and other organic matter carried by rivers and streams. It is typically very fertile and is found in river valleys and deltas. However, there are certain states in India that have very little alluvial soil area. One such state is Arunachal Pradesh.

Arunachal Pradesh is located in the northeastern part of India and is known for its diverse topography, ranging from high mountains to deep valleys. Due to its mountainous terrain, the state has very little alluvial soil area. Here's why:

1. Geographic location: Arunachal Pradesh is situated in the eastern Himalayas and shares its borders with Bhutan, China, and Myanmar. The state is characterized by rugged mountains and deep gorges, making it unsuitable for the deposition of alluvial soil.

2. High elevation: The average elevation of Arunachal Pradesh is around 900 meters, with many peaks exceeding 4,000 meters. The high altitude and steep slopes prevent the accumulation of alluvial soil, as the sediments carried by rivers and streams are rapidly transported downstream.

3. Fast-flowing rivers: Arunachal Pradesh is crisscrossed by several large rivers, including the Brahmaputra, Subansiri, and Siang. These rivers have a high gradient and carry a significant amount of sediment. However, due to the steep slopes, the sediments are quickly eroded and transported downstream, leaving little opportunity for alluvial deposition.

4. Glacial influence: The state is also influenced by glacial activity, with several glaciers present in the higher reaches of the Himalayas. Glaciers erode the land and transport large amounts of rock debris, but the deposition of alluvial soil is limited due to the high elevation and steep slopes.

In contrast to Arunachal Pradesh, states like Uttar Pradesh, Uttaranchal (now Uttarakhand), and Madhya Pradesh have extensive alluvial soil areas. These states are located in the Indo-Gangetic plain, which is known for its fertile alluvial soils deposited by rivers like the Ganges and Yamuna over thousands of years.

In conclusion, Arunachal Pradesh has very little alluvial soil area due to its mountainous terrain, high elevation, fast-flowing rivers, and glacial influence.