I found your family tree which shows Robert and his wife Ina. When you post, provide the link. It helps identify the criteria information (birth date, etc) and family information of the person you seek. It helps volunteers widen searches and also identifies what you already know. And, your ability in genealogy and computer systems, so you won't get patronizing suggestions:http://trees.ancestry.com/tree/5002327/person/74024472?ssrc
For the record, other researchers and archives:
Most of what I find, you have, or have seen yourself. I did throw some suggestions below, but you appear to have this knowledge.
Your tree shows Robert had lived in the Mountain Dell area of Unitah Co, UT, as shown in the 1900/1910 (This area of Daggett County was formed out of Unitah in 1918). In 1910 was living in Manila, as a Ranchman (employee). So, it appears he lived in the same general area for many years. Of note: was the Bucket O'Blood Saloon, which was near the Uncle Jack Robinson cabin (one of the first pioneers. The cabin is a feature of the Flaming Gorge Nat'l Recreation Area). The saloon was frequented by such outlaws as Butch Cassidy and the Sundance Kid the McCarty boys and the Curry Gang
In the 1920 Census, he and his wife were living in Linwood, enumerated January 1920. He was a farmer/rents farm, rented his residence (may or may not have been the rented farm land). He died in Rock Springs, Sweetwater, WY 8 June 1920. Ina Mae (Sadlier), his wife (married Mar 1900 in WY), was living in Linwood, Daggett Co, UT in 1920, died 2 Dec 1935 in Burnt Fork, Sweetwater Co, WY. Your tree did not show children (Ina was about 33 when they married). The 1910 Census shows Ina had two living children, total number born not shown. None shown in the 1920 census.
Just for the possibility, I ran his name on the Bureau of Land Management to see if he had obtained land through the Homestead Act. None found.
I checked the Utah Deaths and Burials 1888-1946, no findings.
Yes, in WA State there were many cemeteries moved. The flooded ones are fully identified and many names identified as to where they were moved; but that doesn't help here. One of our great cemetery transcribers shows one cemetery near Kettle Falls (the entire old town was moved). Her transcription identifies 174 unidentified burials were removed to Inchelium, that cemetery transcription does identify some of the moved remains: I did check for similar data for Utah, without success. This area, due to low population, doesn't seem to have the interested persons to do such work.
The Manila Cemetery. It is shown on www.findagrave.com
I did a check of names from the 1920 census showing Robert, against names in the Manila Cemetery. It appears Robert was one of the oldest on the forms. A Peter Miller, age 57 (1863) is on the census, a Peter Miller, born 1880 is in the cemetery, but doesn't appear to be the same person. An Amos Hill, age 63 is on the census, but not shown in Manila. So, IF any of these people died in Linwood and were buried there first, they don't show up in Manila either. The Manila Cemetery listing shows 461, it may not be a full transcription.
"IF" he was buried in Linwood, his record might have been lost by 1958+. Stones are lost, broken, unreadible, if he had one to begin with. His record at the new place of internment might have been lost, or not transcribed. Even those that are "fully" transcribed, graves are missed, stones broken, etc.
The Death Certificate. The name of the informant is important. IF it was a family member, they might have fully known where he was to be buried. A mistake on the form could have occured, or changes made to plans after it was written. I've seen this occur. The cost of transportation, burial expense, etc.
Location. He had family, or Ina's family in Wyoming, per your records. The DC might have identified cause of death, if he died to be with family or just sudden accident or health related. If they owned a ranch, sometimes burial occured there. Ina's place of burial should also be checked, I've seen the "lost" suddenly appear in such a case.
The Bureau of Reclamation. They don't remove/replace cemeteries. They contract such work. There probably isn't any record other than a contract, payment. The name of the company probably won't do any good. But, it might help you knowing the remains were moved. It also might identify IF there was a cemetery there anyway. I checked a bunch of records. The US Geological Survey identified Linwood as being Historical, but no Historical Cemetery was listed. From reading online data, some of the residences were just burned rather than moving/taken down.
Newspaper. Since he lived in this area for at least 20 years, the local newspaper (if they had one) "might" have identified "something" about him. Obits were not as common then, or even the same type. A true obituary (by definition, especially then) was written by a reporter about the rich, famous, infamous, or victim of accident or crime. A death notice might appear where he died, or in Linwood, area.