I only find one Marmaduke Maxwell in the US census, in 1920 and 1930 in Clatsop County, OR.  I've printed the census pages.  Let me know if you want them.  In 1920 he was living alone in Ecola Voting, age 77, single, retired but also listed as a farm laborer, born in England, parents born in England.  In 1930 he was living alone in Cannon Beach, owned his land and home worth $7000 (lots of $$ in 1930 and way more than his neighbors), age 88, single, retired, self & parents b. England, immigrated to the US in 1873 and had been naturalized a citizen.  I did not find an obituary for him.  The reference to the Morning Oregonian is a story about a Gov. Marmaduke in Louisiana and his opionions about a case involving someone named Maxwell. No relation at all.