The Face on Mars is a Mega Temple.

The artifacts were shards and fragments, mostly. Probably the most interesting item I had the chance to examine was a carved stone pipe with what I believe were Atlantean inscriptions. We think an ancient Martian soldier (probably a human transplanted from ancient Earth) carved it to smoke some sort of local herb, and then discarded it when he was close to getting caught by a superior officer.

There were pieces of metal with characteristics similar to the reports of wreckage from Roswell. They had symbols written on them, not Atlantean, probably Grey.

Most of the items appeared deceptively primitive, like they were built to look ancient when they were new. I think most of the clay and stone pieces were actual part of the shell of a more advanced mechanism whose workings didn't survive the ages. Mars is a harsh environment, after all, and not everything holds together long enough to make it into the archaeological record. We couldn't carbon date any of this stuff, none of it was organic (but the ancient stone-covered mechanism might have been organic technology.)