Could be a very old grave marker, that was lightly engraved, but hard to see now due to chemical weathering. I saw some stone markers that early Pioneers died on along the morman trail. The names on them could be barely seen any more, due to being exposed to the elements over the last 170 years
Looks like an old grave marker to me. My wife and I have been going to old cemeteries for years for her genealogy of our families. I have seen a lot just like this. Some will have faint names or markings on them but most are either highly eroded or were just plain.