Valuable Top-Secret Load

I did a lot of hitchhiking back in the 70's when I was much younger. It was the thing to do in those days. I remember hitchhiking west on I-80 and reached the I-80/I-76 split west of Ogallala, NE. about sunset. I jumped a nearby farm fence and hiked a ways back into the grassland to set up camp for the night. Got my little camp fire started when another hitchhiker showed up asking if he could share camp with me for the night. "Sure", I said. The rest of the night was uneventful. Small talk then into the sleeping bag to sleep. I woke up at sunrise the next morning - I'm guessing around 5:30-6:00. Packed up my gear and started hiking back towards the interstate when I saw a large military semi-truck with jeeps and personnel carriers in front and behind it and a helicopter flying overhead. To this day, I wonder what was so valuable/secret that it required that much protection and security.