The Redridge Steel Dam, constructed between June 1900 and November 1901, replaced a wood crib predecessor on the Salmon Trout River near Redridge. With copper production booming and the Copper Range Company jockeying to establish its dominance south of the Portage Lake, a dam that could serve both the Atlantic and Baltic mills nearby was critical. The peculiarities of the location, however--such as the presence of sandstone rather than solid bedrock--required an innovative approach. Under the guidance of consulting engineers John F. Jackson and Foster Crowell, the Wisconsin Bridge and Iron Company poured a concrete base to serve as surrogate bedrock. Upon that base, they built a gravity dam of structural steel, one of only three ever constructed in North America.

The dam was an unequivocal succcess and a remarkable accomplishment in hydraulic engineering. Both mills were, until their closures in 1912 (Atlantic) and 1922 (Baltic), able to wash some 5,000 tons of rock with the water diverted daily from the structure. At the time of its nomination for historic status in 1985, researchers noted that the massive steel dam--the largest of its kind in the world--had not exceeded flood stage since 1939, a testament to the methodical civil engineers behind its construction.