cryptobiotic crust

A living skin on the surface of desert soil, formed by a community of cyanobacteria, mosses, lichens, fungi, and algae that bind soil particles together into a dark, lumpy, fragile crust. Cryptobiotic crusts fix nitrogen, retain moisture, resist wind erosion, and create the conditions for other plants to establish. They are the desert's topsoil — built over decades, destroyed by a single footstep. A boot print in cryptobiotic crust can take 15 to 25 years to recover. On the Colorado Plateau, the crust is everywhere, and the signs asking you not to step on it are the most important words in the landscape.