The present Samdrup Jongkhar and Pemagatshel districts were popularly known by the common name Dungsam. One of the two oral sources explains that the word 'Dungsam' came from the three conch-shape hills surrounding Pemagatshel(present name); It is said that there are three hills(out of many) that resemble conch. Dungkar/dung in Sharchop dialect means conch and Sam would mean three. Thus, dungsam refers three-conch-shape-hills.
The second source has it that there was a lake, called 'Dungtsho Karmathang' on a hill above the present day Khar(in Pemagatshel) known to have revealed a ter (a sacred hidden treasure) from it by Tertoen Pema Lingpa(1450-1521) . The ancestors who settled there(after the lake dried) came to be known as Dungtshogpa, the people of Dungtsho. Latter Dungthogpa was corrupted into Dungsapa and finally became Dungsampa which in turn was the corruption of Dungsapa.
Specifically present Pemagatshel was known as Dungsam Khoidung(village of Cuckoos) while present Samdrup Jongkhar was known by the name Dungsam Khotri untill 1970. Again Khoidung became Khidung; and the place was known by this name untill it became Pemagatshel.
Thus, in 1969, when Lam Sonam Zangpo(who resided in Yongla goenpa) Invited His Holiness Chabje Dudjom Rimpoche to bless and give discourse on "Rinchen Torzoe Wangling" to the people of the place, got its name PEMAGATSHEL, meaning "blissful land of lotus".
note: the above given map must have changed due to some alterations.