First thing to remember is that the Earth (and presumably other worlds with active plate tectonics) looked very different 66 million years ago: here's one map
. So, you're not likely to find anything in the Himalayas -- they didn't start forming until ~50 Mya -- and if you did, it would more likely be a former beach resort than a ski lodge.
Second, the most probable find is some kind of structure: walls, tunnels, foundations. The regular pattern is the give-away. Unless your Gardeners are fanatic recyclers (which they might well be), the next most likely are garbage dumps or landfills. These tend to be big, stable, used over long periods of time, and contain all kinds of durable goods. Look in areas that would have been useful then but are remote now (since we haven't found anything yet). That long bay on the east side of the Andes looks promising: a site on the eastern shore or up a tributary valley could have been uplifted whole as the mountains built and then covered by jungle.