It's taken a while, but I'm making progress on this diorama. I printed a couple of copies of the Smithsonian T.Rex on my resin printer... I forgot that this was
an accurate model so many of the small bones were printed and lost either in the resin or in the forest of supports I needed to add to print this model. Not a big deal, since most of it would be hidden.
I buried the T.Rex and saucer in some acrylic spackle, then painted the result, added some rocks,
clean kitty litter (which was rock sized in 1/72) and some sand from the Kelso Sand Dunes.
This is what I have so far:

You can see the dead alien's arm through the cracked bubble. Earth bacteria can't eat the flesh, so it just dried out and fossilized.
It's hard to see the T.Rex skeleton - I've since dry brushed it with a lighter color to bring out the bones. Here's a slightly better view:

I'm working on the two figures and some extra equipment right now.