To put the whole shenanigans brought upon by that vagrant DjibSomal to rest, Marehan modern territory is because of the honor and glory of Marehan, who have been one of the most prominent Somali clans to move about East Africa in the pursuit of spreading Islam and fighting paganism as we had seen from their prominent role in the Futuh Al Habesha. Marehan are originally from the Darod homeland on the tip of Somali peninsula in the Red Sea and like Gurey said, in modern history hail from the territory of Nugaal, in the area of what is today Sool and southern Sanaag in Somaliland where their Darod kins the Dhulbahante and Warsangeli continue to live.
Encyclopedia of Religion and Ethics by Hastings, sourcing French 18th century writer Gabriel Ferrand, saying Marehan are an important Sultanate controlling most of the Somali northern coast (the province from the Futah anyone?) on the Red Sea 400 years ago
From Journal of the Royal Queen in 1843 highlighting the Marehan homeland in Nugaal
Then Marehan had moved to the West in present-day Ogaden
Then had moved to what is today central Somalia where remnants are still left in the Galgaduud region, but the principal area having been Gaalkacyo in the Mudug region
From Enrico Cerruli, famed Italian explorer of Somalia
From where Cerruli left off, the Marehan were continuously sending warriors to fight the British occupation in the NFD/Jubbaland and we are left with these British records which consistently show the Marehan to be migrating newcomers to the land in British East Africa
It is beneath my dignity as a Somali and particularly as a Sade Marehan of the Darod Jaberti to respond to a representative of one of the single most worthless ethnic groups in the world but rest assured this is more for putting in the record then responding to you, as Oromo.