Angels Demons Or Just Aliens?

In 1998, William H. Keith, Jr., aka Ian Douglas, published the first book in his sci-fi Heritage Trilogy Series entitled: Sempar Mars.

The lead-in on Amazon.com reads: "The Year is 2040. The Marines have landed on Mars to guard the unearthed secrets of an ancient and dangerous alien race: Ourselves". He expands upon a gigantic "what-if" concerning "the face on Mars" in the region of Cydonia and the discovery of alien archaeological sites and technology exposed on the outlying planets.