You may have the census, I did not and needed for research:
The 1900 Census for (Murphy Hot Springs), Big Flat, Owyhee County, ID
Louis E McMahon, born Aug 1857 in Iowa to father born in Ireland, mother in West Virginia, living as employee in the home of Andrew Rogerson. Employed as Stock Herder.
The 1910 Census for Hagerman, Lincoln Co, ID
Lewis E McMahon, age 54, divorced, born in Iowa to father born in Ireland, mother in Virginia, laborer/farm, renting/house.
NOTE: Hagerman became part of Gooding County when Lincoln County was partitioned in 1913.
The BLM Land Patent:http://www.glorecords.blm.gov/PatentSearch/Default.asp
identifies he obtained 116.1 acres on 10/1/1908. The land was in Gooding County, not a town in Twin Falls County.
The land description:
Township 9-S(south), Range 15-E(East), Section 2, the SW part of the SE Quarter
Same as above, with 5 parts additional in the Section 2
Section 11, 1 part
Section 11, 2 parts.
If you want to know where that land was actually located, go to: http://www.esg.montana.edu/gl/trs-data.html
Change State to Idaho, enter Township and Range and Section 2.
The next window has information on the location of the land in Gooding County. It was 1195 meters from Niagara Springs, 3005 foot from the Idaho Trout Hatchery, 1568 meters from the mouth of the Cedar Draw (creek/river).
Now in the center, click on "Switch to TerraServer"
--there is a "new link", just wait and it will go to it.
In the next window, click on the largest blue box (top left over the map) for size, then click on Topo Map (top right over the map).
In this new window is a plat map. The map is filled with Red colored squares, these are Sections. Toward the bottom in the middle, you'll see a red colored "1" in the middle of the Section. In the middle of box to it's left, left click with your mouse. In the next window do it again. You'll now see a red colored "1" in the middle. This is Section 2. A Section has 640 acres
His land was: Section 2, the SW part of the SE Quarter. So mentally divide this square into quarters. In the bottom Quarter, mentally divide it into quarters. So his land was the bottom left corner of that SE Quarter of Section 2. Basically about the middle of the bottom of that Section.
Now click on "South" You'll see the red "11" for Section 11. His land in that section was probably attached to the land in Section 2, so it was in Section 11, above the Snake river. You'll now see Niagra Springs. His land was north west of Twin Falls, and south west of Jerome. The Snake river divides Gooding County and Twin Falls County. In 1908, that area was in Lincoln County, then in 1913 was in Gooding County when that county came into being.
You can zoom out (Top left) and see an overall view. So, between 1908 and 1910, he moved north to Hagerman. It "appears" he left his land, however, that is unproven.
The Hagerman Valley Family Tree shows Lewis E McMahon marriage to Frances Dillion in Missouri in 1889. They had four children, Samuel born in Virginia in 1891, Mary born in Virginia in 1901, Anna born 1904. This is NOT the correct Lewis E. McMahon that was in Idaho in 1900. Other family tree's identify that Lewis as being born in 1865. Another shows him born in 1857 in Missouri. AND, if you have already reviewed the 4 Mar 1889 death as being an infant, that information is also wrong on this tree. People when you are doing family genealogy, do NOT just click on a leaf on Ancestry.com. There are FAR to many "genealogy volunteers" finding the wrong people and they get into the system. So, there is no connection to the person in the tree to the correct Lewis E. McMahon.
The link given for the University of Idaho doesn't work, as you probably witnessed. (the "uideaho" is the problem). I did a search on the site. For Research Help, you set up an appointment...so you have to go there. There manuscripts had no listings for McMahon
The link for the Owyhee Co Historical Society didn't work; but it is just about visiting their museum:www.visitidaho.org/thingstodo/view-attraction.aspa?id=30780
I've found most historical societies won't do much research, those that do charge "donations". Based on the location of his residence in the 1900 census (out in the middle of no where); and, that he moved out by 1908, doubt there would be much information there.
There are two volunteers in Gooding County on the Random Acts OF Genealogical Kindness... READ THE GUIDELINES FIRST:http://www.raogk.org/idaho2.htm
Perhaps Coy Jones is in a position to review county records. He may also have a knowledge of locations of burial records/cemetery records. (Most cemeteries across the land aren't transcribed, those that are have missed graves, broken or unreadible stones or markers, or totally missing).
County records: Since Gooding County came out of Lincoln County in 1913, you would have to look in both for records...unless upon creating Gooding County local records stayed there.
Marriage/Divorce. Marriage records for that time period would be at the County Clerk/County Recorder's Office. Divorce records would be at the Clerk of the Superior Court. Most States require local Court Clerks to maintain the archives of court records. They might have also heard probate there also.
Property: He lived in Hagerman during the 1910 census; but was renting.
Where is he? Since he had lived in Gooding County from 1900 to 1910, he "might" be there. But, he was still only 54 at the time of the 1900 census. He didn't appear to have roots.
Do you have his records prior to 1900? I couldn't find him in the 1880 census, but didn't look all that hard, didn't look previous. If he had most of his siblings still around in one area, he may have returned there. But, I couldn't find him at all in 1920 using a good number of different search techniques.