Almost certainly the reason the book was one of the prizes was that it was written by a resident of Carlsbad. George B. Markle IV is actually better known for his writings on health; his most cited work, at least at first glance, seems to be a work published in the November 1988 American Medical News satirizing the push for organ donations among executed prisoners, and several other works I've come across (usually letters to editors) show the same interest in general medical ethics. He was an M.D. and general surgeon -- is still listed as practicing, although I don't know how extensively. According to the blurb on the back of the book, he was born in Hazelton, PA and graduated from Yale and the University of Pennsylvania. The Markles are a very old, and historically very wealthy, family in that area; all sorts of things are named after them.
The book is an adventure story of a deliberately old-fashioned kind. The blurb on the back gives this explanation:
George B. Markle IV is a doctor of medicine, a general surgeon, an artist, philosopher, lecturer, columnist and writer. He was raised on good literature and deplores the dearth of writers today who can hold the attention of all ages as could H. Ryder [sic] Haggard, Robert Lewis [sic] Stevenson, H. G. Wells and others of the past who told marvelous stories without filth, explicit sex or gratuitous violence.
Here is an adventure story - call it a science fiction novel, if you will - that harks back to the days when a book could be spellbinding without being degrading or sordid.
The publisher, as you might guess from a blurb like that, seems to be a small private publishing firm; I'm not even sure if it still exists. Nonetheless, the description is really rather accurate. There is something rather H. Rider Haggard-ish about the story, there is no explicit sex, and there is no gratuitous violence. Rather than sex and violence, the story relies on suspense, and does so, if my memory is correct, quite as well as one could wish.
It all starts when an archeology professor joins an expedition to the Yucatan. Things go horribly wrong when their plane is forced down in a little-known and dangerous part of the jungle, where they discover the ruins of the long-lost Teka civilization and learn the terrible secret of their downfall....