Metal Valley is a giant junkyard that Charlie and Max go to find parts for a fighting bot after Noisy Boy was destroyed by Midas. It specializes in, well, metal. In the movie, there are giant cranes lifting things such as beams, scraps etc. There is also a subway train in the background.
Going to Metal Valley is like going Christmas shopping for metal. They have everything, even robot parts (and Atom). In the robot section, there are walls of parts ranging from heads of Gen 1 bots to other metal things I can't explain. When Charlie and Max go there, Max is slips and almost slides off of a cliff into a valley, but before he can fall off, he gets caught on Atom's outstretched arm. Later, Max stays to dig out Atom and bring him using the cart and asks Charilie to get the cart back at the top of the cliff. back while Charlie leaves him and tells him: "If you want that piece of junk, you go get the cart yourself"! Only a good and caring father would leave their kid at the bottom of a trench in the rain at night!
The discovery of Atom
When Max doesn't listen to Charlie and stays near the cliff, the ground falls away underneath him, and he slides down the cliff face. Thankfully, he gets caught on Atom's outstretched arm. Why an entire G-2 unit is buried there is unknown, nor is it known whether or not there may be more older model robots in the metal valley.