Along highway 20 from Idaho Falls heading toward Yellowstone National Park, green and golden fields dominate the fertile plain of the Snake River. The circular areas indicate extensively irrigated farmland. The white dunes developed towards the end of the last ice age approximately 10 000 years ago when the global climate started to become warmer and drier. Lakes and rivers dried up leaving fine sand behind. Continuous winds from the south west blew the sand in northeasterly direction, passing lava fields which are quite dark in the picture.