Last one is definitely the best one. Looks like a shell casing from an alien weapon ... or maybe it’s an alien grenade, which would also explain the lack of actual aliens in the photos; they all ran away when that thing landed :)
The 90 degree angle is odd but most of the straight lines in the other photos look like weathering (which could be by wind) of sedimentary rocks.
This is not a great example, but it’s something I found quickly by searching for “weathered Sedimentary Rocks” on google images:
The round one reminds me of a bedpan or toilet :D
