How hard would it be to detect evidence of previous earth-based intelligent species? The people of Chaco canyon lived about 1000 years ago. They build an exte

How hard would it be to detect evidence of previous earth-based intelligent species? The people of Chaco canyon lived about 1000 years ago. They build an extensive system of stone paved roads. From personal experience I can say that the wind-blown sand and desert vegetation make it impossible to recognize these roads on the surface. These roads were first recognized from aerial photographs. BUT, they were first discovered many years before by a researcher who saw the profile of a road in an excavation. He published a photo in a paper that included the wry note that they looked just like a road.