Please Help To Identify This Postal Souvenir Sheet

I found this and I do not know what is is. I think I remember seeing this recently in the US Specialized Catalog but I don't remember where. When I saw it, I thought I had one.....then poof could not find the sheet and then poof again and can't find the page in the catalog.
Any help is appreciated.
Thank you,
Robert

Great. Thanks! I knew someone here would have the answer.
Thanks again,
Robert

Noted in the introduction to the Souvenir Card section of the specialized catalogue prefix is SC_. Values given are $50 with gum $8 without gum.

According to the write-up on the Mystic website -- "These cards, depicting the White House, were actually printed aboard the truck!"

That is not correct. All the Philatelic Truck sheets were printed by the Bureau of Engraving & Printing in DC. However, some were packaged in rolls, like coil stamps, and run through a miniature demonstration "press". This chopped off the souvenir sheets but did not actually print them. Unfortunately it was slow and sometimes jammed, so in order to move people through the truck more quickly individual sheets were just handed out at the end of the tour.

That's awesome.
Someone earlier was asking about "ephemera", here is a spectacular example of it!