It stands in the middle of one of the linked plazas of a remote, dusty, fallen Pueblo complex that was abandoned, probably because of drought, sometime about 1200 C.E..
It’s not a grave. Ancestral Puebloans didn’t do graves with headstones.
It looks shrine-ish. The unassuming shrines of the Pueblos are often a careful pile of stones.
BETSY JAMES: Worldbuilding and Wilderness 
I am reminded of an article written by Santa Clara Pueblo member and architect Rina Swentzell, “An Understated Sacredness.” You can find the three-page article online. It talks about a similar shrine on one of Santa Clara Pueblo’s sacred mountains.