Ruins is a novel by Kevin J. Anderson.
Ruins features a dense background revolving around some fiction, but mostly fact, regarding the history of the ancient Maya civilization. Mulder and Scully are sent to investigate the mysterious disappearance of a UC-Berkely (I think) archaeology team, composed of students, in the Yucatán which is a region in Mexico. The university team vanish from their last known location: an ancient pyramid and smaller temples coomposing the 'city' of Xitaclan. Xitaclan is a little- known area, and most explorers who visited the site in the 18th or 19th century, even as early as the 16th or 17th century, never returned... When Mulder and Scully arrive, alongside an expert in the archeology field Vladimir Rubicon, father of the outstanding young explorer/scientist (?) Cassandra Rubicon who was leading the expedition. As the story progresses, Dr Rubicon (Sennior) disappears and is found dead. I won't give away to much, but Scully enters the cenote, an ancient sacrificial pit filled with water and also the site of Dr Rubicon's body. Scully, in an ancient diving suit which belonged to Cassandra, discovers the bodies of the 4 members of the team- minus Cassandra... Then things start to go wrong.The natives that lead the two agents to the jungle in the first place, constantly disappear but then return the next day. This time they don't come back. You'll have to read the book to find out what happens next but I will tell you that the U.S militay becomes involved...
An excellent read and just as good compared with Kevin J. Anderson's other fantastic novel, Ground Zero. I don't know iif you can still find the novels but I picked up the books cheap at a library book sale for like an Aussie dollar each (Yes, I'm an Aussie but British by birth). Anyway, read these and other X Files novels by Kevin and also Charles Grant (author of Goblins and Wirlwind) with novels for slightly younger readers (10-11+) which are written by Les Martin. Whatever X Files novels you read, they are all fantastic and worth purchasing and reading...