During the same era, it is clear that the same Smithsonian was making extensive evidence of giant natives disappear as well. Fortunately there we have way too much hard evidence still in the ground and bits and pieces do show up as well as actual written accounts made during contact years.
I have posted on this before and it is clear that this region needs a careful and public reconnaissance to establish real parameters of what could be plausible. We do this in mining all the time. In fact that is the only reason that this area is shut off.
What is new to me is the extensive use of Egyptian place names just there and no where else that i am aware of. My first testable conjecture is to suppose a nineteenth century enthusiast got out there and created all this. But that will be in the public record. All that needs to be researched. We had a similar problem with Aztlan near Lake Superior. The artifacts drove the later naming and this could well have happened here.
It is also reasonable that local discoverers drew the reporting scientist to the site as well. Their intent and motives need to be resolved as well if possible. Land promoters never quit. However the story as told is rich and unique. It is possible that the writer knew that he could not officially publish and chose to do this to establish the record.
Way more compelling is the actual closing of the site itself. If there is nothing there why is it closed?