I found the Hagerman Valley Family Tree and asked Linda Smith to contact you. She has information about his family.
Lewis's parents were married in Iowa but he was born Aug 1857 in Virginia. On 4 March 1889 he married Frances Dillon in Lamar, Barton Co., MO. This info is from the Hagerman Valley Family Tree.
In 1900 Louis was living in Big Flat, Owyhee Co., ID.
Louis E. McMahon b. IA, Aug 1857, employee, stock herder.
In 1910 he was living in Hagerman, LIncoln Co., ID but he was divorced.
He died 5 July 1917 in Gooding, ID according to the Hagerman Valley tre.
McMahon died July 5, 1917, Lincoln Co. per death cert 018516. Source: BYU Idaho, http://abish.byui.edu/specialCollections/famhist/Death
You can request a copy of his obituary from Random Acts Genealogical Kindness. go to raogk.org, read guidelines, choose Idaho, choose ALL as the county and choose one volunteer.
Contact the Shoshone Public Library, shoshone.lili.org/ .