Electrical grounding question

Thinking about it more, I'm going to need to pull the wires out and install 4 gauge. Currently has 6 gauge but the run is 120ft to the barn. The run from the barn to the shop is 60ft so I'm definitely going to need 4 gauge if I'm running off 50amp breakers for that length.

I was able to get the fish tape 90ft until it comes to a dead stop. I can also get it to go 30ft from the opposite end before it comes to a dead stop. There's either some sort of blockage there or there is a junction box or something under the ground. I'm hoping I can use the wires to pull the new wires through because I don't think fish taping is going to make it and I really don't want to dig into the yard playing guess and check on the blockage.