Witness Cool Sandstone Formations at Castle Rock State Park

Los Gatos, Ca – From sandstone to redwood trees, Castle Rock State Park is a Bay Area hiking spot that you don’t want to miss.

About the Park

Los Gatos, Ca – State Park

Science Spotlight: Sandstone at Castle Rock

During our visit to Castle Rock State Park, we were captivated by the carvings of sandstone that lined the park’s trails. The erosion in the sandstone has created interesting patterns over time, which are awesome sights along the hike.

The sandstone at Castle Rock is made mostly of large-grain sand held together by calcium carbonate “cement”. Sandstone naturally has thin cracks along the formation of the rock. Slightly acidic rainwater (rain is made slightly acidic because of water’s reaction with carbon dioxide in the air) is able to penetrate the stone through the cracks, dissolving the calcium carbonate as the water moves into the rock during the wet season.

During the dry season, the water on the inside of the rock is drawn to the surface, bringing along the dissolved calcium carbonate with it. This movement weakens the interior of the rock and strengthens the exterior of the rock, resulting in erosion patterns that can look like pockets. Over time, this process can also produce large caves. As you hike along Castle Rock, be sure to keep your eye out for such formations.

For more information on Castle Rock Geology, feel free to check out this article by the Portola and Castle Rock Foundation!

Park History

The area that we recognize as Castle Rock State Park used to be a network of trails used by the Ohlone people to transport goods from the coast more inland.

The California Gold Rush was the first major source of transformation for the park. Similar to the story of Huddart Park, Castle Rock State Park became a source of lumber for the booming population in the San Francisco Bay Area. Farming in the area also impacted the habitat as orchards were planted to sustain the people living there.

Locals who loved the landscapes around the area began to purchase small plots of land to be enjoyed by the public. In 1968, the area was designated as a State Park after the land was donated to the state by the Sierra Club and Sempervirens Fund.

Visit the Park

Please note that there is an $8 parking fee. Dogs are not allowed in the park.

We recommend checking out the waterfall viewing platform and Goat Rock during your visit. Be sure to bring a camera to take photos of the beautiful sandstone formations!

Here are some helpful resources to plan your visit:


Author: Taylor Crisologo

Taylor studied biology at Cornell University, where she worked with the Cornell Lab of Ornithology on projects ranging from breeding herring gulls off the coast of Maine to dancing lyrebirds in Australia’s Blue Mountains. When she’s not researching great places to experience Bay Area nature, you can find her birding or reading a book at home with her husband and their two indoor cats (Max and Penelope).

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