I have absolutely no idea what type of “mysterious” boulder with an “Egyptian” carving of the Apis bull the show plans to investigate this coming week, but America’s Stonehenge is someplace I’m very familiar with. The site is an arrangement of various small stone grottos and a ring of small standing stones located in Salem, New Hampshire.
The “sacrificial table” is actually a colonial-era lye-leaching stone used in soap-making. Similar stones were also used for apple pressing and other tasks. The image below at left is a known apple-pressing stone, and the image at right is the “sacrificial table.” I think you can see they are virtually identical in form, just as the lye-leaching table is as well.
Later, alternative writers abandoned the Celtic hypothesis and suggested the site was built by Phoenicians, citing as evidence ambiguous scratch marks on some of the rocks (likely tool marks from quarrying) that fringe writers like Barry Fell found to be evidence of not one but three ancient languages: Phoenician, Ogham, and Iberian-Punic. These alphabets are particularly easy to “find” in random scratch marks because they are composed largely of straight lines and angles.
If the site as it currently stands is a modern fake, there is evidence of “megaliths” at Mystery Hill. Native Americans came there thousands of years ago and used the large boulders in the area to chip away stone tools. This left behind large stone cores from the quarrying that could be mistaken for fallen megalithic architecture. (And who knows, maybe some ancient Native group thought it would be cute to arrange them artistically.)
It is often said that H. P. Lovecraft based the stone circle atop Sentinel Hill in The Dunwich Horror (1928) on Mystery Hill, and nearly every guidebook to the site or to weird things in New England repeats the claim. However, many authors say Lovecraft visited in 1937—impossible, since he lay dying in a Providence hospital—or other years long after Dunwich was written. As Lovecraft scholar S. T. Joshi has pointed out, there is no evidence Lovecraft visited the site prior to writing the story, and the only evidence he ever saw it was the much later recollection of H. Warner Munn that he was fairly certain he must have taken Lovecraft to see the site sometime in the 1930s. If that was the case, there might be an echo of Mystery Hill in the stone circle and sacrificial slab featured in “The Diary of Alonzo Typer” (1935), but Lovecraft’s familiarity with the general concept of stone circles from his reading of ancient history does not require such direct influence.