They look like rocks. Rocks that happen to be shaped like other objects we are familiar with, but rocks nonetheless.

The following are all natural formations on earth. No reason that funky shapes couldn't form naturally on mars as well:

https://media.wired.com/photos/5932899f4dc9b45ccec5ecc7/mast...

https://i.pinimg.com/originals/e4/d0/ae/e4d0ae2f92fe13e20564...

http://takeyourbackpackandgo.com/wp-content/gallery/turkey-3...

https://steemitimages.com/DQmbxS1aPuPcUQ8cFhYKea6Po9si9XgZfi...

http://lh3.googleusercontent.com/-h1dmTrqoj4w/Tmawblc-q7I/AA...

http://lh4.googleusercontent.com/-HwJr24FabWE/Tmb4cFoxI5I/AA...

http://lh3.googleusercontent.com/-Y2hOy9AYewo/TmawM-0NUrI/AA...

https://cdn2.wanderlust.co.uk/media/7651/magazine-1186.jpg?w...

https://www.intltravelnews.com/images/2013/11/big/bolivia7.j...