A friend sent me the link to a fascinating short video about a huge Sri Yantra which was discovered in August 1990 in the Oregon Desert.
The Sri Yantra is a very holy symbol of the Divine Mother. This yantra in the desert is a perfect design of about 400 metres in width and length and is carved in a dry lake bed in a remote area of the Oregon desert. It was etched 7 centimetres deep into the extremely hard, sun-baked dry bedsurface. The complex structure has a perfect design and is oriented precisely in the North-South direction. There were no traces of footprints or tire marks in the ground. You can read more about it here.
You find other huge mysterious signs on earth like this huge man in the Australian desert. And here is an article about a German artist carving beautiful Sri Yantras in metal.
Photo from the video