David Eccles, now twenty, helped build houses and cut wood in the canyons. He went to Wyoming as well as to the mines at South Pass to freight goods, and later worked in the Union Pacific coal mines. He earned enough to buy a yoke of oxen, and returned to Ogden, where he took a contract to cut and haul logs in Ogden Canyon. He also entered into a partnership with his bishop, David James, to work a sawmill in the Monte Cristo area east of Ogden.

In 1874 for three months Eccles attended Louis Moench's school in Ogden. There he learned to "figure," a talent he magnified in subsequent business transactions. At Moench's school David met Bertha Marie Jensen, a Danish convert-immigrant, whom he married in 1875. Bertha went with him to the mountains to cook for Eccles and his employees at the mill.

Within ten years David had cleared $15,000 from his enterprises and partnerships and launched out with three undertakings: A new retail lumber yard in Ogden, the Eccles Lumber Company; a sawmill, shingle mill, and general store at Scofield, a coal mining district in eastern Utah; and operation of small mills near Hailey and Bellevue, Idaho, where he provided lumber to the incoming miners and their suppliers in the Wood River area. In three years there, Eccles and his partner, A.E. Quantrell, had earned $50,000. When the Wood River mines failed, Eccles set up a mill and general store at Beaver Canyon, near Idaho's Montana border, which provided ties and lumber for the Utah and Northern Railroad, which was under construction between Ogden and the Montana mines.