In which part of Assam is the 'Terai Zone' situated?

The term 'Terai' refers to the low-lying, marshy belt of alluvial land that runs immediately south of the Himalayan foothills, wherever India's northern mountain front meets its river plains.

Assam touches the Himalayas and Bhutan only along its northern edge, so its Terai tract — the north-bank foothill strip across districts such as Udalguri, Darrang, Sonitpur, and Lakhimpur — necessarily falls in the state's North Zone.

• South Zone: this tract borders the Meghalaya plateau and Barak Valley hills, a highland edge with no Himalayan foothill contact.

• West Zone: the lower-western plains open toward the Bengal lowlands and the Bangladesh border, built by Brahmaputra floodplain deposits rather than a mountain-to-foothill descent.

• East Zone: this tract extends toward Arunachal Pradesh's upper hills and upper Assam's tea belt, drained by the upper Brahmaputra rather than sub-Himalayan foothill streams.

Because only the northern edge of Assam meets the Himalayan foothill front, the Terai Zone is situated in Assam's North Zone.