It is formed at the level where the soil dries out, so it can be deep or shallow. It is impervious to water and cement-like, so the level of the caliche is as far as any water will penetrate. One of the reasons for the prevalence of flash floods is the presence of caliche near the surface of the desert. The ground can only absorb so much water because the caliche blocks and prevents absorption into lower layers. As a result, much of the water runs off, especially during the summer rainy season when rain comes in faster downpours with little time for the water to be absorbed.
Caliche is present in soils that have little calcium.
They combine with particles that are there and harden very slowly. In other places, calcium is washed away because it penetrates deeply and eventually reaches the groundwater and is carried away. In the desert it doesn t get that far because there s not enough water to wash it deep enough to reach the level of the groundwater. In places there are thick, hard layers of caliche. These layers probably began to slowly form 100,000 years ago, cementing par-ticles and even rocks together.