Geoglyphs, sometimes called intaglios or giant effigies, are large figures constructed through the removal of surface rocks, soil or vegetation to reveal lighter underlying earth. Or stones and earth may be heaped together to construct the image. The figures are often so large they are only recognizable when viewed from the sky.

Perhaps the worlds most famous geoglyphs are the Nasca Lines of Peru, constructed 1,500 to 2,000 years ago. The exquisitely detailed figures of birds, mammals and geometric shapes, such as zigzags, spirals and triangles, measure up to 1.2 miles in length. In the United States, more than 200 mammoth figures were fashioned into the desert surface along the Colorado River from southern Nevada to the Gulf of California.

For more than 60 years natural erosional processes, human activities and encroaching vegetation have attacked the targets, completely erasing some and leaving others scarcely visible. Targets graded into the soil have fared the onslaught poorly while the swastikas, made from piles of rock and soil, are persisting slightly better.

• Photos provided courtesy of the United States Geological Survey through http://www.terraserver-usa.com.
• Photos of Kirtland AAF bombing ranges still to come.