Head of Muddywater Creek
Not currently an official name.

Thomas Douglas
5th Earl of Selkirk
Wikipedia
These mountains were originally called “Nelson’s Mountains” by David Thompson [1770–1857], after Horatio Nelson, the hero of Trafalgar.
After the union of the North West Company and the Hudson’s Bay Company [1670–] in 1821, the mountains were renamed in honour of Thomas Douglas, 5th Earl of Selkirk [1771-1820].He was noteworthy as a Scottish philanthropist who sponsored immigrant settlements in Canada at the Red River Colony.
Descriptive.

Doug Taggart with Horses. Date unknown.
Valley Museum & Archives Society
Named by James McEvoy [1862–1935] after S. Derr, a packer and guide from Edmonton.
Fourteen miles in a straight line from the Athabasca, Derr Creek, the largest tributary of the Miette, fiows in through three separate mouths. The valley is here wider than elsewhere and the dry open tract of grassy land between the branching mouths of Derr Creek is known as Dominion prairie.
— McEvoy 1900