When you enter the Rock City area of Mount Diablo California state park, you can find a small parking lot towards the top that places your next to Wind Caves. This is an area where sandstone rock has been eroded away leaving large pocket holes in the stone:
Although the name “Wind Caves” gives the impression that the wind has formed these hole ridden rocks, an information sign gives a better explanation of the process:
Erosion Creates Dramatic Rock Sculptures
Along the trail here in Rock City, you will see dramatic caves sculptured in the sandstone. Though commonly called “Wind Caves,” these cavities have a more complex origin.
These cavities began to form when the sandstone once buried far below the Earth’s surface was exposed in recent geological time during the uplift of Mt. Diablo. Rain, mixed with carbon dioxide from the air, formed weak acidic water that ran over and into the rock. It dissolved the calcite cement that acts as a “glue” holding the sand grains together. Each summer, heat drew water out of the rock and, over the centuries, evaporation left a hard carbonate crust on the surface.
Here and there, the crust cracked and fell away exposing the weakly cemented sandstone inside. The softer material eroded more quickly than the crust, leaving behind the cavities. This sculpturing process continues today.
These are fun to look at and explore (although they have unfortunately been covered in graffiti). One discovery that you will make is that plants have been able to eek out an existence in the most unlikely of places amount the sandstone formations:
For those not satisfied with seeing the formations from the bottom, it’s also possible to make it to the top using a series of footsteps that have been worn into the sandstone:
It’s definitely a fun place to take photos and explore for an afternoon. For more information on how you can help protect and preserve this state park, you can get information at Save Mount Diablo or on their facebooke page
