I downloaded the "Download the Ancient Landscape Lines and Geoglyphs Collection here" file. I didn't look at all of the placemarks, but I looked at quite a few.

My guess would be many/most of these are artifacts left over from oil and gas exploration.

Just curious, SatAM17, how would one go about determining the age of these sorts of images? You've made the assertion that they're "Ancient", how do you know they're not more than a few decades old?