You are right, they are power lines and sewer trails for the utility companies to go through. Most of the time in that area they are not gated and that attracts the folks with 4x4's. Let me tell you from personal experience, don't go there, they are illegal.
When I got my first JK I was oblivious to the illegal/legal thing. I figured it wasn’t right but did it anyways. Well one day a cop showed and was ready to take us to jail and impound our rigs (my jeep, my brothers 4 wheeler and truck) but by some chance he let us off with a warning. I talked to him for a few minutes and he said they could take us to jail over night, impound the vehicles, fine us up to $600 and if we did any damage to the land we would have to pay to fix it. He also said the best rule of thumb is if it isnt your land, a public ORV park or if you don't have written permission from the owner in your hands you shouldn’t be there.
After that, I have never been back. If it isn’t a forest road or ORV park, I don’t go there. Just don’t buy into the “man I have been going for years and never seen a cop” or the “well there are no signs saying to keep out so it’s good to go”.