A lot of people mistakenly believe that all pipelines are public property. This is blatently false.
In fact, MOST piplines are privately owned. They are either owned by the company, or they are owned by landowners whom the company has an agreement with that allows the pipeline to traverse their property.
I have a natural gas pipline that goes through our land.
Remember... assumptions about public land CAN get you arrested for trespassing. I can tell you that from past experiences with trespassers.