Another random "drawing" from nature - windblown layers of sand at Padre Island National Seashore.
A google search led me to several more found drawings:
TheFeltProduction - Part 1
TheFeltProduction - Part 2
Kirsty Hall's Accidental Drawings (a term sometimes used interchangeably with Found Drawing)
Lorraine Glessner's Found Drawing Friday, images in sand
For a definition of found drawing, click here. I've posted this link before but it's worth a repeat.