The Santa Cruz Sandhills occur on Miocene marine sediments and sandstones of the Santa Margarita formation (right)--a highly weathered arkosic (high feldspar content) sandstone. 

As evidence of their marine origins, the Sandhills feature many fossils of sand dollars (upper left), bivalves (lower left), and gastropods, as well as sharks teeth. Thick beds of fossil sand dollars (right) are found underneath the soil surface in Sandhills habitat between Ben Lomond and Scotts Valley. The presence of this layer is correlated with the occurrence of ridges which support sand parkland--a rare community within the Sandhills.

Known as the Zayante Series, the soils derived from the weathering of the Santa Margarita formation contain greater than 90% sand particles, and thus drain very rapidly (upper left). The light grey soils are also poorly developed and have low organic matter. As a result, Zayante soils have low availability of nutrients and soil moisture, and are not conducive to plant growth. This is especially true during the summer drought when temperatures are high and soil moisture is scarce.

So while Felton loam (upper right) supports lush forests including Coast Redwood Forest, adjacent outcrops of Zayante soil support unique communities of plants and animals adapted to the Zayante soils and the hotter, drier conditions they create.