Some sandstone in the Santa Cruz Mountains have variable levels of calcium carbonate segmentation resulting is certain parts being softer than others. The heavy rainfalls in our mountains contain carbon dioxide from the air which seeps into the sandstone and dissolves the softer areas of calcium carbonate holding the sand grains in place. During our dry season (we do have a short one,) the calcium carbonate is drawn to the rock's surface forming a deposit that resists erosion. This leaves the uncemented sand below to crumble away. The resulting caves and honeycomb formations are called tafoni.

There are three areas in the Santa Cruz Mountains, all off of Skyline Boulevard (Highway 35,) that are particularly known for their tafoni. The most well known is at Castle Rock State Park. The sandstone here is hard enough that climbing is allowed and on 80-foot high sandstone outcropping is particularly popular.