Possible that he died in or near Rackerby which is where the family home is/was. Buried at the Brownsville Cemetery in California.
Sources
Grandmother's verbal account and find-a grave
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DNA Connections
It may be possible to confirm family relationships with Luther by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
However, there are no known yDNA or mtDNA test-takers in his direct paternal or maternal line.
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Luther:
"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MFPF-R8L : 19 February 2021), Luthor A Day in household of A P Day, Deek Creek, Allen, Kansas, United States; citing enumeration district ED 2, sheet 18A, NARA microfilm publication T9 (Washington, D.C.: National Archives and Records Administration, n.d.), FHL microfilm 1,254,372.