Bisti zoo - rock eggs

Sandstone in the Bisti Badlands weathers into a multitude of imaginative shapes - including a bestiary of animals real and imaginary. These are two eggs - of an unknown rock animal.

These items are rare, even in the Bisti. I believe they are formed when heavy runoff pulls a little clay off the bottom of a channel, and rolls it into a small ball. The ball rolls along, picking up more clay, like making a snowman. This continues until the clay ball rolls through a deposit of sand and pebbles, which coat the surface and keep more clay from sticking.

Bisti Wilderness in northwest NM.