Why are there giant concrete tunnels in the desert?

Too much conjecture. However, since you mentioned the curvature of earth - Please do an earth curvature experiment. A laser test across Puget Sound will suffice. Since you seem to like citing NASA's data, ten miles from shore to shore will suffice. According to them, there should be a 66.6 feet drop at ten miles. So, a laser 2 feet above the water should not be seen at 2 feet above the water on the other side across this span of because of the assumed 33 feet hump between the two points. If you are true to your name - "Physics Girl", there should be zero excuses to doing this experiment. Since, you have 1.3 million subscribers and the flat earth argument is posted on many you-tube channels - this experiment request should be eagerly accepted. Thanks