Portrait of the Gunzerker as a Young Man is a level-specific challenge found in Thousand Cuts. It is worth 5 Badass Ranks, and tells why Salvador began searching for The Vault.
The first ECHO is found near the entrance, in a small corner behind the vending machines.
The second ECHO is found in next to a small hut in a slightly hidden place near the bridge made of a Hyperion supply crate.
The third ECHO is found under the big bridge leading to the initiation room. One of the metal panels is dislocated, and the space under the floor can be accessed.
The final ECHO can be found in a corner next to the room protected by the electric barrier, south of the initiation room.