The Railroad
First of all, there are two railroads that went and go by the name Missouri and North Arkansas, at different times, and different slants of a large X.
The first is well documented in the book The North Arkansas Line by James R. Fair, Jr.; ISBN No. 8310-7077-3 (which I happen to have a copy of). It went in a NW to SE diagonal from Joplin, MO, to Helena, AR. Parts of it date back to the 1880s. The M&NO ran on trackage rights from Joplin to Neosho, then its own physical rails, which were in two sections, started down to Wayne, MO, which is now a ghost town between Washburn and Exeter. There the M&NO tracks joined onto the Frisco line, so that the M&NO ran on track rights the short distance down to Seligman, MO, where it again took off on its own tracks down through Butler Hollow toward Eureka Springs, AR, where it originally had ended for some time, before being extended down to the Mississippi River at Helena by 1909 - the year that Harry was born.
That M&NA went through several periods of hard times and receiverships, and in 1935 (when Harry was 26 years old) the name died completely when it was reorganized as the Missouri and Arkansas. That lasted until 1949, when the railroad again had to reorganize; some of it being ripped up, and the remainder being organized into different, smaller railroads, including the Arkansas and Ozarks (when Harry was 40 years old). All of it died out by 1960 (when Harry was 51 years old), and most of the tracks were removed by 1962 - only leaving a small excursion line at Eureka Springs. The aforementioned book was written in 1969.
The other railroad going by the Missouri and North Arkansas name was organized much later. It runs on a NE to SW diagonal from Monett, MO to Van Buren, AR. The only overlap with the original M&NA are the few miles of track between Wayne and Seligman, MO on what was the Frisco line, and which (as mentioned before) the original M&NA had trackage rights on to connect its northwest section with its southeast section. Thus, ironically, the two railroads have no tracks in common - the new M&NA being ever so close to the long torn-up tracks at Wayne and Seligman. It still operates today as a small freight rail line that occasionally gives excursion trips through the Ozarks.
The Man - Harry R. Scroggins
Here things get a bit frustrating for the researcher. After several hours of web searching, the only thing available on Harry is his much-too-quiet FindAGrave entry. I even re-read the book to see if he happened to be mentioned in it, but he was not. Since the grave marker also mentions the A&O, and given the typical working years of the life of Harry Scroggins, and the depiction of a steam locomotive on the grave marker, it is most likely that the M&NA engraved on his marker is the original railroad. Perhaps they decided not to clutter it up by also etching in the "middle name" of the M&A years, but chose to only engrave the name of the railroad that he began working for, and its name when he was forced to retire because of its demise.
But as to what Harry did for the M&NA and the A&O could not be determined from extensive web searches. Was he a conductor? An engineer? A fireman? A brakeman? A station master? A yard master? A telegrapher? A clerk? A gandy dancer? If I ever find out, I will happily update this waymark description!
One thing is for sure from his grave marker: Harry R. Scroggins was a railroad man!
The Inscription
Beautiful artwork of a 4-8-4 Dixie type locomotive, its tender with the number 800 on it, and a crummy (caboose), and the words: M&NA AND A&O RAILROAD. Only problem is that, according to the locomotive roster (pages 288 to 290 in the book), the M&NA never had a 4-8-4 locomotive. It never had a locomotive larger than a 4-6-4 Hudson. But we can forgive the modern artist who probably only had photos of "those old trains" to work with, and not the knowledge of what Harry would have actually worked around.